Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂
The magnetic susceptibility and magnetization measured along the b axis of a KTb(WO₄)₂ single crystal was investigated experimentally in the temperature range 70 mK–6 K and in magnetic fields up to 8 T. The results allow us to make conclusion that singlet magnet KTb(WO₄)₂ undergoes an antiferromagn...
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| Zitieren: | Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ / E. Khatsko, C. Paulsen, A. Rykova // Физика низких температур. — 2011. — Т. 37, № 12. — С. 1315–1317. — Бібліогр.: 11 назв. — англ. |
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irk-123456789-1188062017-06-01T03:04:19Z Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ Khatsko, E. Paulsen, C. Rykova, A. Краткие сообщения The magnetic susceptibility and magnetization measured along the b axis of a KTb(WO₄)₂ single crystal was investigated experimentally in the temperature range 70 mK–6 K and in magnetic fields up to 8 T. The results allow us to make conclusion that singlet magnet KTb(WO₄)₂ undergoes an antiferromagnetic phase transition Tc = 0.65 K. 2011 Article Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ / E. Khatsko, C. Paulsen, A. Rykova // Физика низких температур. — 2011. — Т. 37, № 12. — С. 1315–1317. — Бібліогр.: 11 назв. — англ. 0132-6414 PACS: 75.50.Ee, 75.30.Cr, 75.40.Cx, 75.25.–j http://dspace.nbuv.gov.ua/handle/123456789/118806 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Краткие сообщения Краткие сообщения Khatsko, E. Paulsen, C. Rykova, A. Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ Физика низких температур |
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The magnetic susceptibility and magnetization measured along the b axis of a KTb(WO₄)₂ single crystal was investigated experimentally in the temperature range 70 mK–6 K and in magnetic fields up to 8 T. The results allow us to make conclusion that singlet magnet KTb(WO₄)₂ undergoes an antiferromagnetic phase transition Tc = 0.65 K. |
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Article |
| author |
Khatsko, E. Paulsen, C. Rykova, A. |
| author_facet |
Khatsko, E. Paulsen, C. Rykova, A. |
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Khatsko, E. |
| title |
Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ |
| title_short |
Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ |
| title_full |
Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ |
| title_fullStr |
Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ |
| title_full_unstemmed |
Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ |
| title_sort |
evidence for low-temperature antiferromagnetic phase transition in ising singlet magnet ktb(wo₄)₂ |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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2011 |
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Краткие сообщения |
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http://dspace.nbuv.gov.ua/handle/123456789/118806 |
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Evidence for low-temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO₄)₂ / E. Khatsko, C. Paulsen, A. Rykova // Физика низких температур. — 2011. — Т. 37, № 12. — С. 1315–1317. — Бібліогр.: 11 назв. — англ. |
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Физика низких температур |
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2025-07-08T14:40:45Z |
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1837090102165110784 |
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© E. Khatsko, C. Paulsen, and A. Rykova, 2011
Low Temperature Physics/Fizika Nizkikh Temperatur, 2011, v. 37, No. 12, p. 1315–1317
Short Notes
Evidence for low-temperature antiferromagnetic phase
transition in Ising singlet magnet KTb(WO4)2
E. Khatsko1, C. Paulsen2, and A. Rykova1
1Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine
47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: khatsko@ilt.kharkov.ua
2Institut Neel, CNRS, BP 166, F-38042 Grenoble Cedex 9, France
Received April 27, 2011
The magnetic susceptibility and magnetization measured along the b axis of a KTb(WO4)2 single crystal was in-
vestigated experimentally in the temperature range 70 mK–6 K and in magnetic fields up to 8 T. The results allow us
to make conclusion that singlet magnet KTb(WO4)2 undergoes an antiferromagnetic phase transition Tc = 0.65 K.
PACS: 75.50.Ee Antiferromagnetics;
75.30.Cr Saturation moments and magnetic susceptibilities;
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.);
75.25.–j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized
electron studies, synchrotron-source x-ray scattering, etc.).
Keywords: magnetic susceptibility, magnetization, singlet magnet, phase transition.
Alkali-rare-earth double molybdates and tungstates
have been actively studied for a long time. Many com-
pounds of this class are characterized by a strong magnetic
anisotropy of the rare-earth ions, a low local symmetry,
and a pronounced chain structure. The electronic spectrum
of rare-earth ions in the crystalline field usually has low-
lying excited levels, and that leads to the possibility of re-
organization of the corresponding electronic states both by
an external magnetic field and by displacements of the
ions. This is responsible, in particular, for the magnetic-
field-induced structural phase transitions observed in vari-
ous compounds of this class [1–5]. In the case of non-
Kramers rare-earth ions the lowest electronic state often
form a quasi-doublet with a gap Δ of the order of few K,
well separated from the rest of the spectrum. The magnetic
dipole and exchange interactions in these compounds are
of the same order of magnitude. Therefore, singlet and
excitonic types of magnets can be realized in these com-
pounds (in the second case the interactions are insufficient
to induce magnetic order suppressed by the gap Δ [6,7]. In
the non-Kramers doublet case the contribution to the mag-
netic properties of the crystal from the higher-lying excita-
tions of the rare-earth ions are also unusual [6]. All of
these circumstances cause great interest to the study of
such systems. Here it is possible to study a number of topi-
cal questions in solid state physics in a comparatively sim-
ple situation. Among such topics are the interaction of
electronic excitations with lattice vibrations (the Jahn–
Teller effect, polaron effects, etc.), structural phase transi-
tions taking place by unusual scenarios (incommensurabili-
ty, strong fluctuations), and nonlinear regimes of micro-
wave energy absorption, which are comparatively easy to
achieve here because of the long relaxation times of the
elementary excitations [8,9].
One member of this family of compounds that has prac-
tically escaped study is KTb(WO4)2, which contains the
rare-earth ion Tb3+(7F6) with an odd number of electrons.
X-ray studies of the magnet KTb(WO4)2 have shown
that this compound belongs to the monoclinic class C2/c
with a chain structure [10]. There are 4 formulae units per
elementary cell with cell parameters: a = 10.653 Å, b =
= 10.402 Å, c = 7.573 Å, β = 130.76°. Crystal structure is
represented in Fig. 1. The Tb ions form chains along [101]
direction, distance between nearest Tb3+ is 4.071 Å.
The angular dependence of the magnetic susceptibility
[10] shows that at low temperatures a purely Ising aniso-
E. Khatsko, C. Paulsen, and A. Rykova
1316 Low Temperature Physics/Fizika Nizkikh Temperatur, 2011, v. 37, No. 12
tropy with only one component of the moment along the b
axis is realized in this compound. The temperature depen-
dence of the susceptibility has a maximum at T = 1.2 K,
but the experimental temperatures were not low enough to
make sure that the phase transition exist.
According to resonant studies in KTb(WO4)2 [11] the
non-Kramers magnetic ion Tb3+ has a quasi-doublet
ground state separated by an energy gap δ ≈ 1 K which is
well separated from the rest of the spectrum. The magnetic
dipole and exchange interactions are of the same order.
The rare-earth compounds with non-Kramers magnetic
ions often belong to the class of so-called singlet magnets,
which can exhibit unusual magnetic properties because of
the presence of a rather large energy gap between the states
of the quasi-doublet. As the relationship between the val-
ues of the gap δ and the magnetic interactions I varies, the
magnetic properties of these compounds undergo radical
changes. In particular, there exists a critical value of the
ratio δ/I above which spontaneous magnetism becomes
impossible even at zero temperature. However, this critical
value depends substantially on the properties of the inte-
ractions and foremost, on the character of their spatial ani-
sotropy.
The goal of the present study was to look for the exis-
tence of a magnetic phase transition and, if it exists, inves-
tigate its features.
The measurements were carried out with a SQUID
magnetometer developed at the Institute Néel equipped
with a miniature 3He–4He dilution refrigerator allowing
measurements down to 70 mK.
As the nonzero magnetic moment exist only along one
axis b [10], we investigate magnetic properties along this
axis. The magnetic susceptibility along the b axis of
KTb(WO4)2 single crystal was investigated experimentally
in the temperature range 70 mK–6 K in small magnetic
field of 85 Oe. The results are presented in Fig. 2. The
temperature dependence of the susceptibility has a maxi-
mum at Т = 1.2 К. Above this temperature ( )Tχ is de-
scribed by Curie–Weiss law with negative (antiferromag-
netic) Curie temperature –2 K.Θ = Below 1.2 K the sus-
ceptibility drops sharply and below 0.4 K become
practically independent on temperature. Such behavior is
typical for a magnetic phase transition in the antiferromag-
netic state and is described by mean field theory for singlet
magnet [10]. The transition temperature was determined
from the maximum of derivate dχ/dT is Tc = 0.65 K.
The magnetization curves M(H) along the b axis were
studied in magnetic field up to 8 T in temperature range
80 mK–4.2 K. The results are shown in Fig. 3. The satura-
tion magnetic moment is 8.9 ,Bμ which is somewhat
smaller than the calculated values for Tb3+ ion 9.7 .Bμ
X Z
Y
Tb
W
K
Fig. 1. View of the KTb(WO4)2 structure along the [101] direc-
tion: the W polyhedra are dark, the Tb polyhedra are light, and
instead of the K polyhedra only the position of the central atoms
are shown. The X, Y, and Z axes correspond to the crystallograph-
ic axes a, b, and c (taken from [10]).
Fig. 2. Temperature dependence of the magnetic susceptibility of
the KTb(WO4)2 single crystal along the b axis.
0 1 2 3 4 5 6 7
0.002
0.004
0.006
0.008
0.010
0.012
0.014
�
,
em
u
/g
T, K
H = 85 Oe
H b||
Fig. 3. Field dependence of magnetization of the KTb(WO4)2
single crystal along the b axis.
0.25 0.50 0.75 1.000
1
2
3
4
5
6
7
8
9
10
H, T
T = 80 mK
T = 1.2 K
T = 600 mK
T = 900 mK
M
,
�
B
Evidence for-low temperature antiferromagnetic phase transition in Ising singlet magnet KTb(WO4)2
Low Temperature Physics/Fizika Nizkikh Temperatur, 2011, v. 37, No. 12 1317
At low temperatures a nonlinear magnetic behavior was
found, which we explain as the metha-magnetic phase
transition in magnetic field near 0.2 T. Such a transition
can take place when a crystallographic anisotropy is much
larger than the exchange. With increasing temperature the
nonlinearity of magnetization decreases and disappears
above 600 mK. This is consistent with the antiferromagnet-
ic transition temperature determined from the susceptibility
data.
All obtained results allow us to make conclusion that
the singlet magnet KTb(WO4)2 undergoes antiferromag-
netic phase transition with collinear magnetic structure at
Tc = 0.65 K.
In addition we observe the field induced metha-
magnetic phase transition in small magnetic field 0.2 T.
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