Materials Chemistry and Physics 131 (2011) 142–150
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Materials Chemistry and Physics
journal homepage: www.elsevier.com/locate/matchemphys
Specific heat and magnetic susceptibility of single-crystalline ZnCr
2
Se
4
spinels
doped with Ga, In and Ce
E. Malicka
a,∗
, T. Gro ´ n
b
, A.
´
Slebarski
b
, A. G ˛ agor
c
, A.W. Pacyna
d
, R. Sitko
a
, J. Goraus
b
,
T. Mydlarz
e
, J. Heimann
b
a
University of Silesia, Institute of Chemistry, ul. Szkolna 9, 40-006 Katowice, Poland
b
University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-007 Katowice, Poland
c
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw, Poland
d
The Henryk Niewodnicza´ nski Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Kraków, Poland
e
International Laboratory of High Magnetic Fields and Low Temperatures, ul. Gajowicka 95, 53-529 Wroclaw, Poland
article info
Article history:
Received 28 January 2011
Received in revised form 23 June 2011
Accepted 29 July 2011
Keywords:
Chalcogenides
X-ray photo-emission spectroscopy (XPS)
Magnetic properties
Specific heat
abstract
The crystal structure, X-ray photoelectron spectra (XPS), dc magnetic isotherm, ac magnetic susceptibility
and specific heat measurements for antiferromagnetic and semiconducting ZnCr
2
Se
4
spinel diluted with
Ga, In and Ce are presented. For all the studied spinels the XPS spectra exhibit the Cr 2p
3/2
splitting of
1 eV characteristic for the 3d
3
electron configuration of the chromium ions. A correlation between the
second critical field H
c2
of the helix to paramagnetic transition and the magnetic specific heat C-peak was
found in (Zn
0.86
Ce
0.08
)[Cr
2
]Se
4
. This correlation weakens for (Zn
0.99
)[Cr
1.92
Ga
0.06
]Se
4
and disappears for
(Zn
0.83
In
0.11
)[Cr
1.73
In
0.14
]Se
4
as the saturation magnetic moment rapidly decreases in the sequence Ce, Ga
and In. The magnetic contribution to the specific heat displays a sharp peak at T
N
and is maximal at the
spin fluctuation temperature of 40 K, which is related to the maximum of the magnetic susceptibility at
the same temperature and at 50 kOe in the spin fluctuation region, evidenced by the entropy exceeding
90% of the entropy calculated classically for the complete alignment of the Cr spins, S
m
= R ln(2S + 1). These
effects are considered within the cation–anion distances in octahedral sites, the cation deficiency and
the spin state of 3d Cr
3+
ions in t
2g
orbital.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
It is well known in literature that ZnCr
2
Se
4
spinel is a matrix
for various diluted systems where the effects of the site disor-
der, lattice frustration and random distribution of spin interactions
create novel potential applications in the spin-based electronic
technology. ZnCr
2
Se
4
orders antiferromagnetically (AFM) at Néel
temperature T
N
= 20 K but high positive Curie–Weiss
CW
= 115 K
[1,2] evidences strong ferromagnetic (FM) interactions. The mag-
netic order is accompanied by structural transformation from cubic
Fd
¯
3m to tetragonal I4
1
/amd symmetry with a small contraction
along the c axis [3,4]. Neutron-diffraction investigations [1,2] have
shown the helical AFM spin structure below T
N
, which results from
a strong ferromagnetic (FM) spin arrangement in the planes per-
pendicular to the [0 0 1] direction of the orthorhombic cell. The spin
orientation between the planes changes by the angle 42
◦
, and the
spin propagation vector along the [0 0 1] is incommensurate.
∗
Corresponding author. Permanent address: Chemistry Department, University
of Silesia, ul. Szkolna 9, 40-006 Katowice, Poland. Tel.: +48 323591627.
E-mail address: ewa.malicka@us.edu.pl (E. Malicka).
The specific heat and thermal expansion studies evidenced a
strong effect of the external field [5]. The sharp first-order anoma-
lies in the specific heat appearing at the AFM transition suggested a
spin-driven origin of the transition, however, the suppression of the
negative thermal expansion by the external magnetic fields might
have pointed to the role of the spin–lattice coupling. In the same
investigation a metamagnetic transition in the critical field H
c1
of
about 10 kOe and T = 2 K, the breakdown of the helical spin arrange-
ment in the critical field H
c2
of about 65 kOe for T = 2 K, and the full
saturation magnetization of about 6
B
per molecule above H
c2
in
the FM state are revealed. The differences between the zero-field-
cooling (ZFC) and field-cooling (FC) susceptibilities indicated a spin
frustration effect [5]. The studies of the complex ac dynamic mag-
netic susceptibility in external magnetic fields in polycrystalline
ZnCr
2
Se
4
spinel [6] and the fitting procedure of the Curie–Weiss
law [7] have shown a parallel spin coupling in FM clusters in the
range between T
N
= 20.7 K and
CW
= 55.1 K visible in a broad max-
imum at 34 K for H = 40 kOe and at 43.5 K for H = 50 kOe in the real
part of ac magnetic susceptibility characteristic for magnetic fluc-
tuations.
Numerous papers described also the influence of various
cationic admixtures on physical properties of ZnCr
2
Se
4
spinel
0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.matchemphys.2011.07.080