Interplay between low dimensionality and magnetic frustration in the magnetoelectric pyroxenes
LiCrX
2
O
6
(X =Ge, Si)
Gwilherm Nénert,
1,
* Masahiko Isobe,
2
Ingyu Kim,
3
Clemens Ritter,
1
Claire V. Colin,
4
Alexander N. Vasiliev,
5
Kee Hoon Kim,
3
and Yutaka Ueda
2
1
Institut Laue-Langevin, Boîte Postale 156, 38042 Grenoble Cedex 9, France
2
Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwa, Chiba 277-8581, Japan
3
CeNSCMR, Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
4
Institut Néel, CNRS/Université Joseph Fourier, BP 166, 38042 Grenoble, France
5
Low Temperature Physics Department, Moscow State University, Moscow 119991, Russia
Received 9 April 2010; revised manuscript received 2 July 2010; published 28 July 2010
We have investigated the magnetic and magnetoelectric properties of LiCrGe
2
O
6
and reinvestigated the
magnetic properties of LiCrSi
2
O
6
. Using superconducting quantum interference device magnetometry, electri-
cal polarization, and neutron diffraction, we give evidence for the presence of magnetic frustration in the
magnetoelectric pyroxenes LiCrX
2
O
6
X =Si, Ge. While pyroxene materials have been widely investigated for
their low dimensional properties, we suggest that the magnetic frustration is likely to play a more important
role into the nature of the magnetic ground state. The existence and possible interplay of low dimensionality
and magnetic frustration resulting in multiferroic and/or magnetoelectric properties in the pyroxenes will
probably open new avenues to tune and investigate the richness of the physic in this family.
DOI: 10.1103/PhysRevB.82.024429 PACS numbers: 75.85.+t, 75.25.-j, 75.47.Lx, 75.50.Ee
I. INTRODUCTION
In recent years, the coupling between magnetic and di-
electric properties in transition metal oxides gave rise to a
significant research effort.
1–3
This effort is governed by the
emergence of new fundamental physics and potential techno-
logical applications.
2–4
Multiferroic materials exhibit simul-
taneously ferromagnetic, ferroelectric and ferroelastic prop-
erties. Contrary to multiferroic materials, magnetoelectric
materials show an induced electrical polarization by a mag-
netic field. A proper understanding of the interplay between
the various physical properties of these two types of materi-
als relies heavily on the knowledge of the detailed crystal
and magnetic structures.
One class of compounds which have been investigated in
this context is the class of pyroxene materials. They have the
general formula AMX
2
O
6
where A is an alcali +I or alkali-
earth ion +II, M is a transition metal ion +II or +III while
X = Si, Ge. These materials have been extensively investi-
gated due to their importance in mineralogy
5–9
and their low
dimensional magnetic properties.
10–15
The recent work by
Jodlauk et al. shed some different light on these materials
motivated by the idea that this family could be a good rep-
resentative of a magnetically frustrated lattice.
16,17
The exis-
tence and possible interplay of low dimensionality and mag-
netic frustration resulting in multiferroic and/or magneto-
electric properties in the pyroxenes will probably open new
avenues to tune and investigate the richness of the physic in
this family. We aim here to present the first evidence for the
interplay between low dimensionality and magnetic frustra-
tion in magnetoelectric pyroxenes.
Lately, we have started to investigate the structural, mag-
netic, and dielectric properties of various ACrX
2
O
6
materials
as function of temperature and magnetic field.
12–14
In this
contribution, we report on the effect of replacing silicon by
germanium in LiCrX
2
O
6
. We have investigated magnetic
properties of LiCrX
2
O
6
X =Si, Ge powder samples using
superconducting quantum interference device SQUID mag-
netometry. Furthermore, in order to allow a comparison with
our previous work on LiCrSi
2
O
6
,
13
we have investigated the
magnetic, magnetoelectric and crystal structures of the py-
roxene LiCrGe
2
O
6
by electrical polarization measurement
and powder neutron diffraction. Magnetic exchange cou-
plings in LiCrGe
2
O
6
extracted from magnetization measure-
ments suggest a magnetic ground state similar to the one
reported in LiCrSi
2
O
6
, however with a less pronounced one-
dimensional 1D character. This is in perfect agreement with
the antiferromagnetic order determined below T
N
= 4.82 K by neutron diffraction. Corroborating the deter-
mined magnetic structure magnetic symmetry P2
1
' / c, the
magnetic field dependence of the electrical polarization evi-
dences a clear linear magnetoelectric effect below T
N
. The
unexpected lower 1D character in LiCrGe
2
O
6
is discussed in
light of the interplay between low dimensionality of the crys-
tal structure and the magnetic frustration in LiCrX
2
O
6
.
II. EXPERIMENT
Polycrystalline samples of LiCrGe
2
O
6
and LiCrSi
2
O
6
were prepared by a solid-state reaction with an appropriate
molar ratio of Li
2
CO
3
, Cr
2
O
3
, and GeO
2
/ SiO
2
. The weighted
mixtures were pressed into pellets and heated at 1273 K in
air for several days with one intermediate grinding.
Polycrystalline LiCrGe
2
O
6
and LiCrSi
2
O
6
magnetization
measurements were carried out by a SQUID magnetometer
in the temperature range of 2–350 K and external magnetic
fields of 1000 Oe. Neutron diffraction measurements were
carried out on a LiCrGe
2
O
6
powder. The precise crystal and
magnetic structures were investigated using high resolution
powder data at 1.7 and 10 K using the D2B diffractometer at
the ILL. The measurements were carried out at a wavelength
of 1.594 Å corresponding to the 335 Bragg reflexion of a
PHYSICAL REVIEW B 82, 024429 2010
1098-0121/2010/822/0244297 ©2010 The American Physical Society 024429-1