The magnetoimpedance effect allows us to estimate the extent of spin dependent scattering in disordered solids. The change in impedance with respect to applied magnetic field manifests through local change in permeability on the surface and it amplifies at defect sites. The local electrical inhomogeneities are expected to aid this effect through spin dependent scattering. The organic conjugated electrical networks provide scope for producing such inhomogeneities formed by path defects and protonic charge accumulation leading to spin dependent scattering. This hypothesis is investigated in the present work taking polyaniline as a prototype network. The electrical inhomogeneities in the network were controlled by selective oxidation and aging in polyaniline. The Giant Magnetoimpedance (GMI) was observed in the electrically inhomogeneous network with the change in electrical impedance of the order of 50%–60% for lower frequencies with prominent capacitive coupling and a change of the order of 200% at higher frequencies with prominent inductive coupling with the application of magnetic field. However, no spin accumulation was observed in the insulating networks formed by a modified oxidative process. This study is expected to serve as a tool to develop frequency selective spin accumulation based magnetic field sensors and oscillator networks.

Research in conjugated polymer networks has led to a significant advancement in plastic electronics due to their unique electrical, optical, and mechanical properties.1 Starting from a simple folded π-conjugated conducting polymer to a cross linked semiconducting polymer network has posed limitations in achievement of efficient device performance due to anisotropic mobility, stray capacitance, and interfacial impedance.2 This is attributed to inhomogeneity intra-chain charge diffusion and inter-chain interactions.3 However, the charge accumulation across the inhomogeneities can be exploited for developing the field effect devices with neuromorphic capabilities.4 These inhomogeneous networks are typically developed with tuning the organic cross linkages to the conjugated backbone,5 or forming a composite.6 One of the simplest ways of forming the conjugated polymer network is a cold pressing of conducting polymers which builds inhomogeneous conducting pathways in the liner or folded conducting polymers (CP).7 These are useful in designing efficient batteries8 sensors9–11 electronic devices12 and electromagnetic shielding.13 These materials show high specific capacitance compared to oxide double layer supercapacitors.14 These CP networks typically show variable range hopping and feeble or no magnetism.15 Magnetism in conjugated polymers is a debated subject of study.16,17 Here the compound being purely made of carbon-nitrogen- hydrogen, we do not expect any explicit magnetic ordering or strong spin orbit coupling but wave function localization across the electrical pathway, which explains the feeble magnetism in it and it mimics other correlation effects.18,19 Further, the magnetoresistance (MR) studies have shown that there is reduction in resistance with magnetic field (negative MR) indicating a ferromagnetic order in such systems debating its origin.20,21 Parish and Littlewood showed that there is possibility of magnetoresistive response created due to inhomogeneities, which serve as voltage dividers and spin dependent scatterers.22 The scattering strength increases the spin accumulation probability23 leading to magnetocapacitance.24 This has led us to look for a mode to tune inhomogeneity in CPs typically achieved by aging25 or chemical denaturing26 and develop spin accumulation based electric elements like magnetoresistor or capacitors.

In the present work, we study the effect of inhomogeneity on spin accumulation strength of a conjugated polymer network formed by cold pressing of polyaniline (PANI) using the magnetoimpedance effect. Cold pressed conjugated polymers are expected to have rich electronic networks formed out of coiling or reticulation of molecular chains.27 With aging, the electrical paths lose protons making a non-conducting region or an electrical inhomogeneity. These develop spin scattering sites due to localization effects. We compare the inhomogeneous PANI’s spin accumulation strength to the non-conducting PANI with relatively larger resistivity. The universal power response theory was used to establish variable relaxation with magnetic fields.

Conducting polymers like PANI are the class of polymers which conduct electricity and are widely used for its conductive character, stability, low production cost and its electrochemical properties in photovoltaic cells, diodes, and sensors. Oxidative polymerization of aniline using HCl and oxidiser like ammonium persulphate is used to form the conducting PANI.28 In this process the quality of the polymer obtained is a strong function of the nature of the oxidizer used and the pH maintained during the process of oxidation.29 Initially, 1.8626 ml of aniline was poured into an ice-cold beaker with deionized water maintained at 1 °C which gave 0.2 M solution. Further, 8.7 ml of HCl was added in 100 ml of deionized water and stirred. Further, 5.702 gm of ammonium persulphate (APS) was added in 100 ml of water, giving 0.25 M of APS. Then APS was added dropwise to aniline hydrochloride mixed solution. At first the solution was colourless. Later, while adding APS to aniline hydrochloride solution, it became pale yellow then blue, green, and finally it turned into a shiny layer on the surface. This solution was spun on a magnetic spinner, then filtered. The reaction mixture was maintained at 1 °C through the process using an ice bath to form a fibrous PANI. We dried it in a furnace for 4 h at 90 °C and finally obtained PANI powder.28,30,31 Typically, the molar ratio of APS to aniline monomer is maintained at less than 1.2 to achieve smooth surface and fine fibers of PANI. But the aim of the work being production of intrinsic defects retaining the fibrous nature, a ratio of 1.25 was maintained as suggested by Fang et al.29 The powder was compressed to get pure conducting PANI. It is known from the literature that the pH of the solution also plays an important role in tuning the defect density of the formed PANI.32 Further this polymer was aged by leaving the powder to the ambient in an aeriated container to develop electrical inhomogeneities for 10 days. Here it is worth mentioning that there was no external dopant or hydration used to alter the conductivity of PANI. Further the sealed powder was cold pressed under 10 Ton pressure for 1 h to form a 3 mm thick block.

In the synthesis of non-conducting PANI a similar procedure was adapted as above except for the use of the oxidant. A 0.2 molar aniline solution was prepared and placed in an ice bath maintained at 1 °C and HCl was added to it. Further, 5.702 g of ammonium dichromate (ADC) was added to 100 ml of water giving 0.25 M ADC. The aniline used for the preparation of PANI was purchased from Sigma-Aldrich and the oxidisers and acid were procured from SD fine chemicals, India. Then ADC was added dropwise to the aniline hydrochloride solution. As in the earlier case at first, the solution was colourless changing the color to black on further addition of ADC. The solution was spun to form the polymer. Here it is important to note that ADC is a strong oxidizer generating a light absorbing polymer powder with lower conductivity.28,33 Further, to reduce the conductivity the powder was washed with 0.1M NaOH. This stabilized the resistivity of the powder to a fixed higher value of the order of a few mega ohms.34 The obtained powder was washed with deionised water and dried.

In both the cases, the dried powder was cold pressed in a 1 cm diameter tungsten die under 10 Ton pressure for 1 h to form a 3 mm thick block as earlier and silver was evaporated with Mansha Vacuum thermal evaporator with 99.90% purity silver chunk as a evaporation source at 4 × 10−5 mbar vacuum pressure to form the electrodes. The thickness of the film was 0.72 μm and copper measuring leads were attached with the silver paint. The arrangement was once again backed at 60 °C for good contact.

Impedance measurements were performed using an AC perturbation signal of 50 mV level in the frequency range 100 Hz to 5.5 MHz with NF-Corporation impedance analyzer. The DC measurements were done using a dual channel Keysight source and measure unit B2902A. Both conducting polyaniline and non-conducting polyaniline were pelletized and silver electrodes were evaporated for contact as mentioned earlier. The voltage was swept from one channel with a scan rate of 0.001 V/s to assess the possibility of charge accumulation whereas the other channel was used for measuring voltage. The forcing voltage was limited to +/− 1 V to avoid extrinsic nonlinear effects. The impedance measurements were averaged over ten sweeps with a single point acquisition for each frequency. These capacitor structures were subjected to a magnetic field, simultaneously measuring the real and imaginary part of the impedance. The magnetic field was perpendicular to device structure and the field was controlled by a programmable Polytronics electromagnet unit. The magnetic field was varied from zero to 1200 Oe in one direction The stability of the magnetic field was ensured during the sweep time.

To understand the charge transport in the inhomogeneous medium created in the form of non-conducting pathways in PANI, we study DC electrical resistance. The non linearity in I–V characteristic will allow us to understand the formation of potential barriers in the transport of charge carriers due to non-conducting pathways.

Figure 1 depicts an ohmic response for “as prepared” PANI. The black color compressed PANI behaves as a conductor showing pure ohmic behavior with non ohmic nature at higher voltages arising due to electron density difference in the electrode and the material under test. The resistivity was of the order of 2.22 × 10−4 Ω-cm in this case. When aged or selectively oxidised (use of different oxidisers and use of NaOH for wash as mentioned in the synthesis section) the transport changes from diffusive mode to hopping mode35 in PANI. Initially in “as prepared” case the transport in PANI will be through the conjugations being a combination of Drude36 or interchange transfer37 like. The protonated region loses the free carriers in the polymer inducing broken inhomogeneous regions in the material. This is expected to change the DC as well as AC conductivity drastically.38 The “aged PANI” above 10 days showed resistivity of 115 Ω-cm. The I–V was modeled as a resistor-capacitor network forming a voltage loop as depicted in Fig. 2 (right corner). The outer region is proposed to be with a finite permittivity ε1 and conductivity σ1 and inner region oxidised will have higher permittivity ε2 and lower conductivity σ2 forming a junction having local current difference I1 and I2 respectively. The following expression represents the region typically used to understand Schottky junctions connected back-to-back.39,
IV=I1I2SinhqV2KBTI1expqV2η1KBT+I2expqV2η1KBT
(1)
where,
I1=A*T2expqϕB1KBT
(2)
I2=A*T2expqϕB2KBT
(3)
where, A* is the Richardson constant 120 A cm−2 K−2, T is temperature in kelvin, q is the charge of electron 1.6 × 10−19 C, KB is the Boltzmann constant 1.38 × 10−23 m2 Kg s−2 K−1, ϕB is the Schottky barrier height and η is the ideality factor. The inhomogeneities in the contact and the barrier are typically modeled by this approach as seen in similar works on SiC-Metal junctions.40 The transmission of electric energy between two insulator-separated by a conductor gives blocking of charge carriers which forms micro capacitor-like structures in a solid (depicted by different colors in Fig. 2). In the aged polymer the insulating region serves a leaky capacitor surrounded by the conductive linkages forming an inhomogeneous network of constant phase elements (CPE).41 The CPE nature causes the electrical network to transform into a low impedance channel for alternating current (AC) contributing to overall reactance. When fit to Eq. (1) the average barrier height of 0.64 eV was estimated indicating formation of a comparatively shallow barrier in the polymer matrix with aging. Here the ideality factor used for the fit was 10.47. The higher value of ideality factor corroborates the claim of inhomogeneous barrier distribution across the metal-aged PANI junction. The “insulating PANI” formed by adding ADC and washed with NaOH had an average resistivity of ∼ 6.2 × 104 Ω-cm (I–V not shown).
FIG. 1.

I–V characteristics of Polyaniline.

FIG. 1.

I–V characteristics of Polyaniline.

Close modal
FIG. 2.

The process of spin accumulation at the junction of inhomogeneous resistive grains in aged PANI is depicted by two different colors (upper figure) which behave like a constant phase element. The lower figure depicts charge transport in fully insulating PANI without spin distinction showing feeble charge current. Right corner depicts a voltage network formed due to inhomogeneous conductivity and permittivity.

FIG. 2.

The process of spin accumulation at the junction of inhomogeneous resistive grains in aged PANI is depicted by two different colors (upper figure) which behave like a constant phase element. The lower figure depicts charge transport in fully insulating PANI without spin distinction showing feeble charge current. Right corner depicts a voltage network formed due to inhomogeneous conductivity and permittivity.

Close modal

Further to know the spin scattering strength and nature of the charge carrier we study the Hall voltage and DC Magnetoresistance in these solids. The Hall coefficient for aged PANI was nonlinear (With magnetic field) and was of the order of ∼214 at 1200 Oe with a negative sign (the data is not shown in the paper) which is higher compared to the earlier reports.42,43 This indicates that the solid is defect rich with majority carriers as electrons.44 The MR with applied magnetic field is shown in Fig. 3, which depicts a transition in sign from negative to positive indicating change of interaction. At low fields spin-spin interaction is expected to be exchange kind (in macrospin approximation) whereas at higher magnetic fields the interaction is dipole kind.45 Considerable MR value of ∼45% is seen at 1200 Oe magnetic field. This large value of MR corroborates the observation of a large value of Hall resistance. The findings are in line with claims by smiler studies46,47 where defects are created by forming composite of electrically distinguishable material with PANI. It is interesting to note that the magnitude of MR is ∼5% in pure PANI at around 2000 Oe with exchange interaction (negative) as per earlier reports.48 Here the inhomogeneities increase spin dependent scattering developing a non saturative magnified MR.49 Here the MR was 45% at 1200 Oe which is higher compared to the earlier reports. The change of interaction from exchange kind to dipolar kind in an inhomogeneous medium is consistent with earlier results where inhomogeneities were created by forming a composite.50 

FIG. 3.

Magnetoresistance in aged PANI.

FIG. 3.

Magnetoresistance in aged PANI.

Close modal
To investigate the extent of spin accumulation and relaxation AC response was studied. The capacitive networks formed by inhomogeneity gives effective reactance at lower frequencies and at higher frequencies the inductiveness dominates. Figure 4, shows the real part of impedance for two different magnetic field values 0 and 1200 Oe respectively for “aged PANI.” The impedance showed capacitive coupling at lower frequencies as expected indicated by knee-like response. To model the response, a simple Debye approach was used, represented by the Lorentzian equation,
Zω=Ro1+(ωτ)2
(4)
Here τ is the characteristic relaxation time and Ro is the offset resistance. It was observed that the difference in offset resistance or the DC resistance was positive of the order of 12 kΩ which is in agreement with the DC-MR observations supporting dipole-like macrospin interaction. Furthermore, the relaxation time observed was of the order of 3.32 × 10−5 s without magnetic field and relaxation time was found to increase with increase in magnetic field. This indicates that the spin accumulation increases with increase in magnetic field forming a localized cloud of charges51 as depicted in upper part of Fig. 2. Increase in localization strength of the inhomogeneous barrier formed by conductivity and permittivity difference increases the effective resistance with magnetic field at higher fields. The charge clusters interact with the 3D disorders contributing to effective change in impedances. Similar strategies of charge localization are efficiently used to harness the functional properties of PANI in literature.52,53 Here, intentionally the ideal Debye model was used instead of other more generic models to account for the effect of magnetic field on the charge cloud or the dipoles with effective macrospin orientation and coherence.54,55 The spin coherence in accumulation at the boundary of inhomogeneity can be better analyzed through the imaginary part of impedance compared to the real.54 
FIG. 4.

Variation of real part of impedance with magnetic field.

FIG. 4.

Variation of real part of impedance with magnetic field.

Close modal

To know the dissipative nature of the capacitive network, the imaginary part of the impedance was studied as depicted in Fig. 5(a). The response was pure Debye kind with relaxation peak at 332 kHz which is the relaxation frequency of the charge cloud. A strong shift in the relaxation frequency was observed in the response function with respect to applied magnetic field indicating change of spin accumulation.52 The width of the Deby peak also increases indicating induction of incoherency in the macrospin precession. It is significant to mention that the spin polarized electron concentration increases in these networks as and the coupling of electromagnetic waves increases with magnetic field altering FWHM of the relaxation peak.54 

FIG. 5.

(a) Change in Imaginary component with frequency at two different magnetic fields. Inset shows fit to Deby model. (b) Normalized imaginary component of impedance with frequency at two different magnetic fields.

FIG. 5.

(a) Change in Imaginary component with frequency at two different magnetic fields. Inset shows fit to Deby model. (b) Normalized imaginary component of impedance with frequency at two different magnetic fields.

Close modal

Decrease in relaxation frequency with magnetic field indicates decrease in mobility56 due to formation of spin oriented localized charge clouds as represented in Fig. 2 and depicted by normalized imaginary part of impedance shown in Fig. 5(b). In total it infers that spin scattering in the aged PANI remains prominently incoherent due to inhomogeneities.

As the perturbation frequency increases, coupling turns inductive, reaching self-resonance observed near 4.5 MHz as shown in Fig. 6(a). The resonance frequency shifts with an applied magnetic field supporting ferromagnetic resonance of macrospins. The spin accumulation affects resonance which could be possibly magnonic in nature. Hence to investigate the scattering mechanism the resonance frequency was plotted with respect to the applied magnetic field as shown in Fig. 6(b).

FIG. 6.

(a) Spin resonance at higher frequencies shifting with the magnetic field. (b) Change of resonance frequency with applied magnetic field.

FIG. 6.

(a) Spin resonance at higher frequencies shifting with the magnetic field. (b) Change of resonance frequency with applied magnetic field.

Close modal
For pure magnonic scattering the resonance frequency with magnetic field shall be following kittle response function, however we did not observe such dependencies. This allows us to infer that the magnonic scattering in such inhomogeneous media is highly dispersive due to multi-magnon scattering and modeling it remains a challenge. As a general practise, we tried to look at the power dependence of the resonance frequency (ωo) with applied magnetic field by fitting, it to a generic power law;
ωo=C×(H)n
(5)
where, C is a constant and n is the power. The fit yielded a power of −0.41 which is a non-Kittel response usually seen in magnetically inhomogeneous solids or granular solids.57 It was found that the resonance frequency shifts to the left, i.e., it decreases with the applied magnetic field indicating a critical damping in macro spin rotations which could be due to inhomogeneities.

There was significant MI in the lower frequency domain where the network couples capacitively.58, Figure 7, shows the impedance change of the order of 50% for two distinct frequencies at 1 and 10 kHz, respectively for “aged PANI” at 1200 Oe. The sign of the MI was positive throughout the magnetic field range indicating a prominent dipole-like interaction59 where macrospins interact with each other via a long-range interaction. The macrospins formed due to defect-correlation, interact over a long-range producing a positive MI. In contrast to DC measurements the low field MI was also found to be positive which could be due to strong coupling of electromagnetic radiation to the defects. To evaluate the nature of macrospin relaxation the MI was fit to power law. The power response was found to be 0.3, indicating the charge transport to be purely blocking kind or accumulative24 with dominant dipole-like macrospin interaction which is in agreement with interpretation of sign of MI. This large AC-MR is technologically important for development of low frequency sensing devices.

FIG. 7.

Change in impedance with applied magnetic field in lower frequency region (with prominent capacitive coupling) for aged PANI.

FIG. 7.

Change in impedance with applied magnetic field in lower frequency region (with prominent capacitive coupling) for aged PANI.

Close modal

As the frequency increases the impedance decreases, setting up the inductive coupling between the device under test and the electromagnetic radiation. Once conductivity goes above a critical limit the inductive reactance increases.60 MI in this region is very important for designing integrated sensors.61 We have investigated the GMI effect in the aged PANI at higher frequencies (in the inductive self-resonance region). A large change in the impedance of the order of 200% was observed here at 4.4 MHz as depicted in Fig. 8.

FIG. 8.

Change in impedance with applied magnetic field in high frequency region (with prominent inductive coupling) for aged PANI.

FIG. 8.

Change in impedance with applied magnetic field in high frequency region (with prominent inductive coupling) for aged PANI.

Close modal

At higher frequencies the test element being inductive, with finite spin vector, permeability will increase, which allows magnetic fields to enter the sample developing a large reactance change.62 This effect is a function of the geometry of the device under test. As observed in literature, due to the significant change in chain structure following carbonization, the reactance of polymer nanofibers reduces, but stays finite at high electric fields.20,63 Here also the MI follows power law and the power of the response function varies from 0.8 to 2 with frequency. The change in impedance has positive signs, indicating that the macrospin interaction remains dipole-like. The interface scattering turns more incoherent with applied magnetic fields depicted by increasing power of response function and magnitude of AC-MR.24 

To compare the study with literature, according to the research by Kim et al. G/SiC-PANI devices have conductivities that are on par with PANI nanofibers on Au electrodes64 which are useful to produce spin scattering. The quantum interference of wavefunctions of electrons propagating along different channels during charge hopping processes in the applied magnetic field and shrinking of localized electron wavefunctions competing exchange and dipole like interaction65 which explains the AC-MR or MI behavior in the present study. Here the study serves as a tool to develop defect mediated magnetic sensors with capacitive as well as inductive coupling with the appropriate choice of perturbation frequency.

For the non-conducting PANI, as expected we observed large DC resistance of the order of 8–10 MΩ depending on the process stability and pH. No aging effect was observed in them. A pellet of resistivity 0.31 MΩ-cm was used for the study. A significant dispersion in the real part of impedance was observed with frequency for non-conducting PANI as shown in Fig. 9.

FIG. 9.

Change in real part of impedance for non-conducting PANI.

FIG. 9.

Change in real part of impedance for non-conducting PANI.

Close modal

The effect of magnetic field on dispersion was found to be minimal. It was further fit to the Debye model as in the earlier case. As expected, at lower frequencies (1 to 10 kHz) there was capacitive coupling with minimal MI. In the Fig. 10, MI was plotted with respect to applied magnetic field at 3.3 MHz, where we expect inductive coupling and significant impedance change.

FIG. 10.

Magnetoimpedance with field for non-conducting PANI.

FIG. 10.

Magnetoimpedance with field for non-conducting PANI.

Close modal

The absence of inhomogeneous charge conducting pathways in the impeding parts reduces the reactance with respect to applied magnetic field giving no significant magnetoimpedance. The observed values of change in AC-MR are sharely due to contacts as explained by Catalan.66 In literature graphene oxide, a non-conducting material, following the Havriliak-Negami dielectric relaxation model revealed significant non-coherent dipolar oscillations that foretold the formation of loosely bound magnetic polaron-like structures because of flaws in the inhomogeneous matrix46 which supports the present study in CP networks. In non-conducting PANI, due to compensated charge networks, no spin accumulation capacitance was observed.

In this study, we have observed the GMI effect in capacitive and inductive coupling regimes of frequency for “aged PANI” mediated by inhomogeneities due to localization effects. The study paves the path for the development of magnetic sensors made of PANI with electrical inhomogeneity. In the capacitive coupling region as well as in the inductive coupling region aged PANI showed dipole-like interaction inferring dominance of impurity scattering. Further, change in the impedance (MI) of the order of 50%–60% for two distinct frequencies of 1 and 10 kHz, respectively at 1200 Oe, with power response of 0.3 supported the nature of interaction of macrospin to be dipole-like. At higher frequency, aged PANI showed a GMI of the order of 200% mimicking spin resonance effect without an ideal Kittel response. However, it can be speculated here that the Magnon scattering was non- Kittel due to the over damping effect of macrospins produced by inhomogeneities depicted by the power analysis of MI response with magnetic field. In non-conducting PANI, no significant magnetoimpedance was observed because of feeble spin dependent scattering depicted by no effect of magnetic field on electric relaxation. Furthermore, the absence of electrical inhomogeneity or inhomogeneous path ways is speculated to be the reason for no magnetoimpedance effect in the non-conducting CP network.

Rajeev Shesha Joshi acknowledges support from the Central University of Karnataka, Vision Group of Science and Technology, Karnataka, and University Grant Commission for financial support. Sukhjot Singh acknowledges Parishkar College of Global Excellence, (Autonomous), Jaipur, Rajasthan for financial support to present the work in an international forum.

The authors have no conflicts to disclose.

Sukhjot Singh: Data curation (equal); Formal analysis (equal); Investigation (equal); Visualization (equal); Writing – original draft (equal). Mallikarjun Rampur: Data curation (equal); Formal analysis (equal); Methodology (equal). Anjali Chetty: Data curation (equal); Formal analysis (equal); Visualization (equal). Rajeev Shesha Joshi: Conceptualization (equal); Data curation (equal); Funding acquisition (equal); Project administration (equal); Resources (equal); Visualization (equal); Writing – review & editing (equal).

The data that support the findings of this study are available within the article.

1.
C.
Weder
, “
Synthesis, processing and properties of conjugated polymer networks
,”
Chem. Commun.
43
,
5378
5389
(
2005
).
2.
Z. H.
Wang
,
C.
Li
,
E. M.
Scherr
,
A. G.
MacDiarmid
, and
A. J.
Epstein
, “
Three dimensionality of ‘metallic’ states in conducting polymers: Polyaniline
,”
Phys. Rev. Lett.
66
(
13
),
1745
(
1991
).
3.
S. T.
Keene
,
V.
Gueskine
,
M.
Berggren
,
G. G.
Malliaras
,
K.
Tybrandt
, and
I.
Zozoulenko
, “
Exploiting mixed conducting polymers in organic and bioelectronic devices
,”
Phys. Chem. Chem. Phys.
24
(
32
),
19144
19163
(
2022
).
4.
N.
Hagiwara
,
T.
Asai
,
K.
Ando
, and
M.
Akai‐Kasaya
, “
Fabrication and training of 3D conductive polymer networks for neuromorphic wetware
,”
Adv. Funct. Mater.
33
(
42
),
2300903
(
2023
).
5.
X. C.
Li
,
T.-M.
Yong
,
J.
Grüner
,
A. B.
Holmes
,
S. C.
Moratti
,
F.
Cacialli
, and
R. H.
Friend
, “
A blue light emitting copolymer with charge transporting and photo-crosslinkable functional units
,”
Synth. Met.
84
(
1–3
),
437
438
(
1997
).
6.
W.
Zhang
,
X.
Zhang
,
Z.
Qin
,
J.
He
,
Y.
Lan
,
W.
Zhang
, and
R.
Yang
, “
Interpenetrating polymer network-based composites reinforced by polysilsesquioxanes: Molecular dynamic simulations and experimental analysis
,”
Composites, Part B
209
,
108604
(
2021
).
7.
O. C.
Gamboni
,
C.
Riul
,
R.
Billardon
,
W. W.
Bose Filho
,
N.
Schmitt
, and
R. B.
Canto
, “
On the formation of defects induced by air trapping during cold pressing of PTFE powder
,”
Polymer
82
,
75
86
(
2016
).
8.
W.
Fan
,
N.-W.
Li
,
X.
Zhang
,
S.
Zhao
,
R.
Cao
,
Y.
Yin
,
Y.
Xing
,
J.
Wang
,
Y.-G.
Guo
, and
C.
Li
, “
A dual‐salt gel polymer electrolyte with 3D cross‐linked polymer network for dendrite‐free lithium metal batteries
,”
Adv. Sci.
5
(
9
),
1800559
(
2018
).
9.
J.
Wang
,
F.
Lv
,
L.
Liu
,
Y.
Ma
, and
S.
Wang
, “
Strategies to design conjugated polymer based materials for biological sensing and imaging
,”
Coord. Chem. Rev.
354
,
135
154
(
2018
).
10.
P. T.
Patil
,
R. S.
Anwane
, and
S. B.
Kondawar
, “
Development of electrospun polyaniline/ZnO composite nanofibers for Lpg sensing
,”
Procedia Mater. Sci.
10
,
195
204
(
2015
).
11.
N. G.
Deshpande
,
Y. G.
Gudage
,
R.
Sharma
,
J. C.
Vyas
,
J. B.
Kim
, and
Y. P.
Lee
, “
Studies on tin oxide-intercalated polyaniline nanocomposite for ammonia gas sensing applications
,”
Sens. Actuators, B
138
(
1
),
76
84
(
2009
).
12.
Z.
Tian
,
H.
Yu
,
L.
Wang
,
M.
Saleem
,
F.
Ren
,
P.
Ren
,
Y.
Chen
,
R.
Sun
,
Y.
Sun
, and
L.
Huang
, “
Recent progress in the preparation of polyaniline nanostructures and their applications in anticorrosive coatings
,”
RSC Adv.
4
(
54
),
28195
28208
(
2014
).
13.
P.
Modak
,
S. B.
Kondawar
, and
D. V.
Nandanwar
, “
Synthesis and characterization of conducting polyaniline/graphene nanocomposites for electromagnetic interference shielding
,”
Procedia Mater. Sci.
10
,
588
594
(
2015
).
14.
K.
Wang
,
H.
Wu
,
Y.
Meng
, and
Z.
Wei
, “
Conducting polymer nanowire arrays for high performance supercapacitors
,”
Small
10
(
1
),
14
31
(
2014
).
15.
A. J.
Epstein
,
W.-P.
Lee
, and
V. N.
Prigodin
, “
Low-dimensional variable range hopping in conducting polymers
,”
Synth. Met.
117
(
1–3
),
9
13
(
2001
).
16.
S.
Kalia
,
S.
Kango
,
A.
Kumar
,
Y.
Haldorai
,
B.
Kumari
, and
R.
Kumar
, “
Magnetic polymer nanocomposites for environmental and biomedical applications
,”
Colloid Polym. Sci.
292
(
9
),
2025
2052
(
2014
).
17.
A. A.
Correa
,
E. C.
Pereira
, and
A. J. A.
de Oliveira
, “
Magnetic properties of conducting polymers
,” in
Emerging Research in Science and Engineering Based on Advanced Experimental and Computational Strategies
(
2020
), pp.
493
510
.
18.
B. I.
Shklovskii
and
A. L.
Efros
,
Electronic Properties of Doped Semiconductors
(
Springer Science & Business Media
,
2013
), Vol. 45.
19.
K. H.
Kim
,
S.
Lara-Avila
,
H.
Kang
,
H.
He
,
J.
Eklöf
,
S. J.
Hong
,
M.
Park
et al, “
Apparent power law scaling of variable range hopping conduction in carbonized polymer nanofibers
,”
Sci. Rep.
6
(
1
),
37783
(
2016
).
20.
K. H.
Kim
,
S.
Lara-Avila
,
H.
He
,
H.
Kang
,
S. J.
Hong
,
M.
Park
,
J.
Eklöf
et al, “
Probing variable range hopping lengths by magneto conductance in carbonized polymer nanofibers
,”
Sci. Rep.
8
(
1
),
4948
(
2018
).
21.
D.
Sun
,
Y.
Zhai
,
K. J.
Van Schooten
,
C.
Zhang
,
M.
Kavand
,
H.
Malissa
,
M.
Groesbeck
,
R.
Menon
,
C.
Boehme
, and
Z. V.
Vardeny
, “
Sign reversal of magnetoresistance and inverse spin Hall effect in doped conducting polymers
,”
J. Phys.: Condens. Matter
30
(
48
),
484003
(
2018
).
22.
M. M.
Parish
and
P. B.
Littlewood
, “
Classical magnetotransport of inhomogeneous conductors
,”
Phys. Rev. B
72
(
9
),
094417
(
2005
).
23.
M. M.
Parish
and
P. B.
Littlewood
, “
Magnetocapacitance in nonmagnetic composite media
,”
Phys. Rev. Lett.
101
(
16
),
166602
(
2008
).
24.
S.
Singh
,
J.
Poojari
,
V.
Bhat
,
R.
Mallikarjun
,
S.
Athikundil Kayakkulam
,
K. P.
Shinde
,
J. S.
Park
,
Y.
Jo
,
P. S. A.
Kumar
, and
R. S.
Joshi
, “
Evaluation of low magnetic field magnetocapacitance effect in Ni–NiO inhomogeneous medium
,”
Appl. Phys. A
129
(
10
),
681
(
2023
).
25.
B.
Sixou
,
N.
Mermilliod
, and
J. P.
Travers
, “
Aging effects on the transport properties in conducting polymer polypyrrole
,”
Phys. Rev. B
53
(
8
),
4509
(
1996
).
26.
A. H.
Majeed
,
L. A.
Mohammed
,
O. G.
Hammoodi
,
S.
Sehgal
,
M. A.
Alheety
,
K. K.
Saxena
,
S. A.
Dadoosh
,
I. K.
Mohammed
,
M. M.
Jasim
, and
N. U.
Salmaan
, “
A Review on polyaniline: Synthesis, properties, nanocomposites, and electrochemical applications
,”
Int. J. Polym. Sci.
2022
,
9047554
.
27.
J. O.
Karlsson
and
P.
Gatenholm
, “
Cellulose fibre-supported pH-sensitive hydrogels
,”
Polymer
40
(
2
),
379
387
(
1999
).
28.
Z. A.
Boeva
and
V. G.
Sergeyev
, “
Polyaniline: Synthesis, properties, and application
,”
Polym. Sci., Ser. C
56
(
1
),
144
153
(
2014
).
29.
F. F.
Fang
,
Y.-Z.
Dong
, and
H. J.
Choi
, “
Effect of oxidants on morphology of interfacial polymerized polyaniline nanofibers and their electrorheological response
,”
Polymer
158
,
176
182
(
2018
).
30.
U.
Rana
,
S.
Mondal
,
J.
Sannigrahi
,
P. K.
Sukul
,
Md. A.
Amin
,
S.
Majumdar
, and
S.
Malik
, “
Aromatic bi-tri- and tetracarboxylic acid doped polyaniline nanotubes: Effect on morphologies and electrical transport properties
,”
J. Mater. Chem, C
2
(
17
),
3382
(
2014
).
31.
K. A.
Ibrahim
, “
Synthesis and characterization of polyaniline and poly(aniline-co-o-nitroaniline) using vibrational spectroscopy
,”
Arabian J. Chem.
10
,
S2668
S2674
(
2017
).
32.
X.
Zheng
,
M. E.
Ali Mohsin
,
A.
Arsad
, and
A.
Hassan
, “
Polymerization of polyaniline under various concentrations of ammonium peroxydisulfate and hydrochloric acid by ultrasonic irradiation
,”
J. Appl. Polym. Sci.
138
(
27
),
50637
(
2021
).
33.
M.
Beygisangchin
,
S.
Abdul Rashid
,
S.
Shafie
,
A. R.
Sadrolhosseini
, and
H. N.
Lim
, “
Preparations, properties, and applications of polyaniline and polyaniline thin films—A review
,”
Polymers
13
(
12
),
2003
(
2021
).
34.
A. G.
MacDiarmid
and
A. J.
Epstein
,
Polyaniline: Synthesis, Chemistry and Processing
(
University of Pennsylvania
,
1992
).
35.
R.
Pelster
,
G.
Nimtz
, and
B.
Wessling
, “
Fully protonated polyaniline: Hopping transport on a mesoscopic scale
,”
Phys. Rev. B
49
(
18
),
12718
(
1994
).
36.
R. S.
Kohlman
,
J.
Joo
, and
A. J.
Epstein
, in
Physical Properties of Polymers Handbook
, edited by
J. E.
Mark
(
AIP
,
New York
,
1996
), pp.
453
478
.
37.
A. J.
Heeger
, “
The critical regime of the metal–insulator transition in conducting polymers: Experimental studies
,”
Phys. Scr.
T102
(
1
),
30
(
2002
).
38.
K.
Lee
,
S.
Cho
,
S.
Heum Park
,
A. J.
Heeger
,
C.-W.
Lee
, and
S.-H.
Lee
, “
Metallic transport in polyaniline
,”
Nature
441
(
7089
),
65
68
(
2006
).
39.
P.
Reddy
and
J.
Kumar
, “
Modified approach to modeling barrier inhomogeneity in Schottky diodes
,”
Semicond. Sci. Technol.
34
(
3
),
035004
(
2019
).
40.
M.
Ben Karoui
,
R.
Gharbi
,
N.
Alzaied
,
M.
Fathallah
,
E.
Tresso
,
L.
Scaltrito
, and
S.
Ferrero
, “
Influence of inhomogeneous contact in electrical properties of 4H–SiC based Schottky diode
,”
Solid-State Electron.
52
(
8
),
1232
1236
(
2008
).
41.
S.
Amand
,
M.
Musiani
,
M. E.
Orazem
,
N.
Pébère
,
B.
Tribollet
, and
V.
Vivier
, “
Constant-phase-element behavior caused by inhomogeneous water uptake in anti-corrosion coatings
,”
Electrochim. Acta
87
,
693
700
(
2013
).
42.
S. M.
Giripunje
and
J.
Ghushe
, “
Preparation, characterization and Hall effect study of conducting polyaniline and polyaniline-ZnO nano composite
,”
Int. J. Appl. Phys. Math.
2
(
4
),
234
(
2012
).
43.
P.
Ghosh
,
A.
Sarkar
,
M.
Ghosh
,
A. K.
Meikap
,
S. K.
Chattopadhyay
,
S. K.
Chatterjee
,
P.
Chowdhury
, and
B.
Saha
, “
A study on Hall voltage and electrical resistivity of doped conducting polyaniline
,”
Czech. J. Phys.
53
,
1219
1227
(
2003
).
44.
Y.
Kumar
,
F.
Bern
,
J.
Barzola-Quiquia
,
I.
Lorite
, and
P.
Esquinazi
, “
Study of non-linear Hall effect in nitrogen-grown ZnO microstructure and the effect of H+-implantation
,”
Appl. Phys. Lett.
107
(
2
),
022403
(
2015
).
45.
S.
Singh
,
K. S.
Kumar
,
Y.
Bitla
,
B.
Kori
,
B.
Hiremath
,
M.
Rampur
, and
R. S.
Joshi
, “
Large low-magnetic-field magnetocapacitance effect and spin accumulation in graphene oxide
,”
IEEE Trans. Magn.
58
(
2
),
1600105
(
2022
).
46.
N.
Tanty
,
A.
Patra
,
K. P.
Maity
, and
V.
Prasad
, “
Tuning magnetoresistance and electrical resistivity by enhancing localization length in polyaniline and carbon nanotube composites
,”
Bull. Mater. Sci.
42
,
198
(
2019
).
47.
J.
Guo
,
Z.
Chen
,
W.
Abdul
,
J.
Kong
,
M. A.
Khan
,
D. P.
Young
,
J.
Zhu
, and
Z.
Guo
, “
Tunable positive magnetoresistance of magnetic polyaniline nanocomposites
,”
Adv. Compos. Hybrid Mater.
4
,
534
(
2021
).
48.
J.
Guo
,
L.
Guan
,
H.
Wei
,
M. A.
Khan
,
X.
Zhang
,
B.
Li
,
Q.
Wang
et al, “
Enhanced negative magnetoresistance with high sensitivity of polyaniline interfaced with nanotitania
,”
J. Electrochem. Soc.
163
(
8
),
H664
(
2016
).
49.
M. M.
Parish
and
P. B.
Littlewood
, “
Non-saturating magnetoresistance in heavily disordered semiconductors
,”
Nature
426
(
6963
),
162
165
(
2003
).
50.
K. P.
Maity
,
N.
Tanty
,
A.
Patra
, and
V.
Prasad
, “
Negative to positive magnetoresistance transition in functionalization of carbon nanotube and polyaniline composite
,”
Mater. Res. Express
5
(
3
),
035034
(
2018
).
51.
V. I.
Krinichnyi
,
S. D.
Chemerisov
, and
Y. S.
Lebedev
, “
EPR and charge-transport studies of polyaniline
,”
Phys. Rev. B
55
(
24
),
16233
(
1997
).
52.
V. I.
Krinichnyi
, “
Dynamics of spin charge carriers in polyaniline
,”
Appl. Phys. Rev.
1
(
2
),
021305
(
2014
).
53.
Y.
Zhang
,
Z.
Yang
,
T.
Pan
,
H.
Gao
,
H.
Guan
,
J.
Xu
, and
Z.
Zhang
, “
Construction of natural fiber/polyaniline core-shell heterostructures with tunable and excellent electromagnetic shielding capability via a facile secondary doping strategy
,”
Composites, Part A
137
,
105994
(
2020
).
54.
K.
Manna
,
R. S.
Joshi
,
S.
Elizabeth
, and
P. S.
Anil Kumar
, “
Evaluation of the intrinsic magneto-dielectric coupling in LaMn0.5Co0.5O3 single crystals
,”
Appl. Phys. Lett.
104
(
20
),
202905
(
2014
).
55.
J.
Xiao
,
A.
Zangwill
, and
M. D.
Stiles
, “
Macrospin models of spin transfer dynamics
,”
Phys. Rev. B
72
(
1
),
014446
(
2005
).
56.
D. C.
Tripathi
,
D. K.
Sinha
, and
Y. N.
Mohapatra
, “
Diffusivity and mobility of non-equilibrium carriers in organic semiconductors: Existence of critical field determining temperature dependence
,”
J. Appl. Phys.
114
(
15
) (
2013
).
57.
G. N.
Kakazei
,
A. F.
Kravets
,
N. A.
Lesnik
,
M. M.
Pereira de Azevedo
,
Y. G.
Pogorelov
, and
J. B.
Sousa
, “
Ferromagnetic resonance in granular thin films
,”
J. Appl. Phys.
85
(
8
),
5654
(
1999
).
58.
P.
Kassanos
,
B. G.
Rosa
,
M.
Keshavarz
, and
G.-Z.
Yang
, “
Power and data communication in wearable and implantable devices
,” in
Wearable Sensors
(
Academic Press
,
2021
), pp.
279
309
.
59.
Y. P.
Kalmykov
,
S. V.
Titov
,
D. J.
Byrne
,
W. T.
Coffey
,
M.
Zarifakis
, and
M. H.
Al Bayyari
, “
Dipole–dipole and exchange interaction effects on the magnetization relaxation of two macrospins: Compared
,”
J. Magn. Magn. Mater.
507
,
166814
(
2020
).
60.
T.
Kim
,
G.
Kim
,
H.
Kim
,
H.-J.
Yoon
,
T.
Kim
,
Y.
Jun
,
T.-H.
Shin
et al, “
Megahertz-wave-transmitting conducting polymer electrode for device-to-device integration
,”
Nat. Commun.
10
(
1
),
653
(
2019
).
61.
N.
Hernández Sebastián
,
N.
Villa Villaseñor
,
F.-J.
Renero-Carrillo
,
D.
Díaz Alonso
, and
W.
Calleja Arriaga
, “
Design of a fully integrated inductive coupling system: A discrete approach towards sensing ventricular pressure
,”
Sensors
20
(
5
),
1525
(
2020
).
62.
M. A.
Corrêa
,
F.
Bohn
,
R. B.
da Silva
, and
R. L.
Sommer
, “
Magnetoimpedance effect at the high frequency range for the thin film geometry: Numerical calculation and experiment
,”
J. Appl. Phys.
116
(
24
),
243904
(
2014
).
63.
S.
Ding
,
C.
Jin
,
Z.
Fan
,
P.
Li
, and
H.
Bai
, “
Sign change of magnetoresistance in Gd-doped amorphous carbon granular films
,”
Phys. Chem. Chem. Phys.
17
(
45
),
30695
(
2015
).
64.
K. H.
Kim
,
S.
Lara-Avila
,
H.
He
,
H.
Kang
,
Y. W.
Park
,
R.
Yakimova
, and
S.
Kubatkin
, “
Thermal stability of epitaxial graphene electrodes for conductive polymer nanofiber devices
,”
Crystals
7
(
12
),
378
(
2017
).
65.
K. D.
Bozdag
,
N.-R.
Chiou
,
V. N.
Prigodin
, and
A.
Epstein
, “
Magnetic field, temperature and electric field dependence of magneto-transport for polyaniline nanofiber networks
,”
Synth. Met.
160
(
3–4
),
271
(
2010
).
66.
G.
Catalan
, “
Magnetocapacitance without magnetoelectric coupling
,”
Appl. Phys. Lett.
88
(
10
),
102902
(
2006
).