Magnetic nanoparticles (MNPs) are extensively used in biotechnology. These applications rely on magnetic properties that are a keen function of MNP size, distribution, and shape. Various magneto-optical techniques, including Faraday Rotation (FR), Cotton-Mouton Effect, etc., have been employed to characterize magnetic properties of MNPs. Generally, these measurements employ AC or DC fields. In this work, we describe the results from a FR setup that uses pulsed magnetic fields and an analysis technique that makes use of the entire pulse shape to investigate size distribution and shape anisotropy. The setup employs a light source, polarizing components, and a detector that are used to measure the rotation of light from a sample that is subjected to a pulsed magnetic field. This magnetic field “snapshot” is recorded alongside the intensity pulse of the sample's response. This side by side comparison yields useful information about the real time magnetization dynamics of the system being probed. The setup is highly flexible with variable control of pulse length and peak magnitude. Examining the raw data for the response of bare Fe3O4 and hybrid Au and Fe3O4 nanorods reveals interesting information about Brownian relaxation and the hydrodynamic size of these nanorods. This analysis exploits the self-referencing nature of this measurement to highlight the impact of an applied field on creating a field induced transparency for a longitudinal measurement. Possible sources for this behavior include shape anisotropy and field assisted aggregate formation.

1.
R.
Hergt
,
S.
Dutz
, and
M.
Zeisberger
, “
Validity limits of the Neel relaxation model of magnetic nanoparticles for hyperthermia
,”
Nanotechnology
21
,
015706
(
2010
).
2.
L.
Tu
,
T.
Klein
,
W.
Wang
,
Y.
Feng
,
Y.
Wang
, and
J.
Wang
, “
Measurement of Brownian and Néel relaxation of magnetic nanoparticles by a mixing-frequency method
,”
IEEE Trans. Magn.
49
(
1
),
227
(
2013
).
3.
G.
Mériguet
,
E.
Dubois
,
M.
Jardat
,
A.
Bourdon
,
G.
Demouchy
,
V.
Dupuis
,
B.
Farago
,
R.
Perzynski
, and
P.
Turq
, “
Understanding the structure and the dynamics of magnetic fluids: Coupling of experiment and simulation
,”
J. Phys.: Condens. Matter
18
,
S2685
S2696
(
2006
).
4.
W.
Reed
and
J. H.
Fendler
, “
Anisotropic aggregates as the origin of magnetically induced dichroism in ferrofluids
,”
J. Appl. Phys.
59
,
2914
2924
(
1986
).
5.
H. W.
Davies
and
J. P.
Llewellyn
, “
Magnetic birefringence of ferrofluids. II. Pulsed field measurements
,”
J. Phys. D: Appl. Phys.
12
,
1357
63
(
1979
).
6.
P. C.
Scholten
, “
First century of colloid magneto-optics
,”
Indian J. Eng. Mater. Sci.
11
,
323
330
(
2004
).
7.
C. V.
Raman
, “
India's debt to Faraday
,”
Nature
128
,
362
364
(
1931
).
8.
M.
Wang
,
C.
Gao
,
L.
He
,
Q.
Lu
,
J.
Zhang
,
C.
Tang
,
S.
Zorba
, and
Y.
Yin
, “
Magnetic tuning of plasmonic excitation. of gold nanorods
,”
J. Am. Chem. Soc.
135
,
15302
15305
(
2013
).
9.
A.
Jain
,
J.
Kumar
,
F.
Zhou
,
L.
Li
, and
S.
Tripathy
,
Am. J. Phys.
67
,
714
717
(
1999
).
10.
T.
Foulkes
,
M.
Syed
, and
M.
Herniter
, “
Engineering pulsed magnetic fields: Designing and building a pulsed. Magnetic field circuit for a Faraday rotation experimental setup
,” in
IEEE 56th International Midwest Symposium on Circuits and Systems
(
IEEE
,
2013
), pp.
497
500
.
11.
R.
Hergt
,
R.
Hiergeist
,
I.
Hilger
,
W. A.
Kaiser
,
Y.
Lapatnikov
,
S.
Margel
, and
U.
Richter
, “
Maghemite nanoparticles. with very high AC-losses for application in RF-magnetic hyperthermia
,”
J. Magn. Magn. Mater.
270
(
3
),
345
357
(
2004
).
12.
R.
Hergt
,
S.
Dutz
,
R.
Muller
, and
M.
Zeisberger
, “
Magnetic particle hyperthermia: nanoparticle magnetism and materials development for cancer therapy
,”
J. Phys.: Condens. Matter
18
,
S2919
(
2006
).
13.
R. K.
Dani
,
Exploring Physical Properties of Nanoparticles for Biomedical Applications
(
Kansas State University
,
Manhattan, Kansas
,
2012
), pp.
65
70
.
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