The nanoparticles of ε-Fe2O3 enriched with 57Fe isotope in amorphous silica matrix were prepared by sol-gel technique starting from a single molecular precursor for both Fe2O3 and silica. From the X-ray powder diffraction pattern ε-Fe2O3 was identified as the major phase and α-Fe2O3 and β-Fe2O3 were observed as minor iron oxide phases. Using the log-normal distribution for fitting the experimental data from the TEM micrographs, the characteristic size of particles d0 ∼ 25 nm was derived. The rather high coercivity of ∼2.1 T at room temperature was confirmed for our nanoparticle system. From the dependences of magnetization on temperature a two-step magnetic transition spread between 100 K and 153 K was indicated. From the 57Fe Mössbauer spectra measured in the temperature range of 4.2–300 K, the hyperfine parameters for one tetrahedral and three octahedral sites of ε-Fe2O3 structure were identified. The in-field spectra in the external magnetic fields up to 6 T were taken both above and below the indicated two-step magnetic transition. Their dependence on temperature and external magnetic field suggests that the first step in the temperature range of 153 K–130 K is related to the spin reorientation of the local magnetic moments in the magnetic sublattices and the second step in temperatures 130 K–100 K may be associated with the intermediate spin–high spin state transition of Fe3+ cation in the tetrahedral sublattice expressed in the change of the hyperfine magnetic field.

1.
L.
Machala
 et al,
Chem. Mater.
23
,
3255
(
2011
).
2.
R.
Zbořil
 et al,
Chem. Mater.
14
,
969
(
2002
).
3.
P.
Brázda
 et al,
J. Therm. Anal. Calorim.
117
,
85
(
2014
).
4.
J.
Tuček
 et al,
Chem. Mater.
22
,
6483
(
2010
).
5.
M.
Popovici
 et al,
Chem. Mater.
16
,
5542
(
2004
).
6.
J.
Jin
 et al,
Adv. Mater.
16
,
48
(
2004
).
7.
S.
Sakurai
 et al,
J. Phys. Chem. C
112
,
20212
(
2008
).
8.
M.
Gich
 et al,
Appl. Phys. Lett.
96
,
112508
(
2010
).
9.
M.
Gich
 et al,
Adv. Mater.
26
,
4645
(
2014
).
10.
S.
Sakurai
 et al,
Chem. Phys. Lett.
458
,
333
(
2008
).
11.
M.
Gich
 et al,
Nanotechnology
17
,
687
(
2006
).
12.
A.
Namai
 et al,
J. Am. Chem. Soc.
131
,
1170
(
2009
).
13.
A.
Namai
 et al,
Nat. Commun.
3
,
1035
(
2012
).
14.
P.
Brázda
 et al,
Cryst. Growth Des.
14
,
1039
(
2014
).
15.
E.
Tronc
 et al,
J. Solid State Chem.
139
,
93
(
1998
).
16.
S.
Sakurai
 et al,
J. Phys. Soc. Jpn.
74
,
1946
(
2005
).
17.
M.
Gich
 et al,
Chem. Mater.
18
,
3889
(
2006
).
18.
M.
Kurmoo
 et al,
Chem. Mater.
17
,
1106
(
2005
).
19.
E.
Tronc
 et al,
J. Appl. Phys.
98
,
053901
(
2005
).
20.
S.
Ohkoshi
 et al,
J. Phys. Chem. C
113
,
11235
(
2009
).
21.
J.
Tuček
 et al,
Appl. Phys. Lett.
99
,
253108
(
2011
).
22.
J.-L.
Rehspringer
 et al,
Hyperfine Interact.
166
,
475
(
2005
).
23.
P.
Brázda
 et al,
J. Sol-Gel Sci. Technol.
51
,
78
(
2009
).
24.
J.
Rodriguez-Carvajal
 et al,
Phys B
192
,
55
(
1993
).
25.
E. N.
Maslen
 et al,
Acta Crystallogr. B
50
,
435
(
1994
).
26.
L.
Ben-Dor
 et al,
Acta Crystallogr. B
32
,
667
(
1976
).
27.
J. E.
Jørgensen
 et al,
J Solid State Chem.
180
,
180
(
2007
).
28.
T.
Zak
 et al,
Surf. Interface Anal.
38
,
710
(
2006
).
29.
T. J.
Daou
 et al,
J. Phys. Chem. C
114
,
8794
(
2010
).
30.
E. R.
Bauminger
 et al,
Phys. B
86-88
,
910
(
1977
).
31.
32.
R. E.
Vandenberghe
 et al,
Hyperfine Interact.
53
,
175
(
1990
).
33.
F.
Bodker
 et al,
Phys. Rev. Lett.
72
,
282
(
1994
).
34.
J. M. D.
Coey
,
Phys. Rev. Lett.
27
,
1140
(
1971
).
35.
E.
Matthias
 et al,
Arkiv. För Fysik
24
,
97
(
1963
).
36.
J.
Kohout
 et al,
J. Phys IV France
7
,
449
(
1997
).
37.
H.
Stepankova
 et al,
J. Magn. Magn. Mater.
177
,
239
(
1998
).
38.
J.
Kohout
 et al,
J. Magn. Magn. Mater.
196
,
415
(
1999
).
39.
E.
Gamaliy
 et al.
J. Magn. Magn. Mater.
242
,
766
(
2002
).
You do not currently have access to this content.