Magnetic properties of an anomalous phase transition around 5 K in YbSb

Article abstract of DOI:10.1016/S0921-4526(98)00709-1

NMR measurements on ¹²¹Sb have been performed to clarify the magnetic properties of an anomalous phase transition around 5 K in YbSb. The external magnetic field dependence of the NMR linewidth was measured above and below the transition temper

Full text of DOI:10.1016/S0921-4526(98)00709-1

Physica B 259—261 (1999) 159—160
Magnetic properties of an anomalous phase transition
around 5 K in YbSb
K. Hashi!, A. Oyamada!ꢀ*, S. Maegawa!, T. Goto!, D.X. Li", T. Suzuki#,
A. Donni$, F. Hulliger%
!Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan
"Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan
#Institute for Solid State Physics, University of Tokyo, Minato-ku, Tokyo 106-8666, Japan
$Department of Physics, Niigata University, Niigata 950-2181, Japan
%Laboratory for Solid State Physics, ETH Zu( rich, CH-8093 Zu( rich, Switzerland
Abstract
NMR measurements on ꢁꢂꢁSb have been performed to clarify the magnetic properties of an anomalous phase
transition around 5 K in YbSb. The external magnetic field dependence of the NMR linewidth was measured above and
below the transition temperature. The additional broadening of the NMR spectrum at the extrapolated magnetic field of
0 T in the ordered state indicates the presence of an antiferromagnetic order of an extremely reduced moment. The
magnetic phase diagram of YbSb was obtained from the temperature dependence of the magnetization under various
magnetic fields. ( 1999 Elsevier Science B.V. All rights reserved.
Keywords: YbSb; Reduced moment; NMR
Yb-monopnictides (YbX: X"N, P, As, Sb) attract
much attention because of their unusual magnetic prop-
erties which come from the competition between the
Kondo hybridization and the RKKY interactions. In
these compounds YbSb has unusual phase transitions as
follows. The Mossbauer spectroscopy measurements has
reported the presence of two-phase transitions at 0.32
and 5 K [1]. On the other hand, neutron diffraction
measurements on the same sample which was used in the
Mossbauer spectroscopy did not detect any long-range
magnetic ordering down to 7 mK [2]. Therefore the
presence of the phase transitions has not been definitive.
We had reported that NMR spectrum of YbSb shows the
abrupt and distinct broadening around 5 K using the
polycrystalline sample YbSb C1 prepared by ETH
group [3]. In this study we have prepared a polycrystal-
line sample YbSb C2 which has better homogeneity than
that for YbSb C1 and performed NMR measurements
around 5 K using YbSb C2.
The polycrystalline sample YbSb C2 was prepared by
a prereaction of the constituent elements in an evacuated
and sealed quartz tube at temperatures up to 700°C,
which is followed by annealing at 750°C for a week. The
X-ray diffraction measurements show that the crystal
structure is NaCl type and the lattice constant is 6.07 A.
The full-width at half-maximum (FWHM) of the diffrac-
tion line corresponding to the +2 2 0, plane in YbSb C2
is about a half of that in YbSb C1. This indicates that the
homogeneity of sample in YbSb C2 is better than that in
YbSb C1. There are small peaks which come from impu-
rities as in YbSb C1. The relative intensity of the impu-
rity peaks to the +2 0 0, peak in YbSb C2 is almost the
same with that in YbSb C1. The NMR measurements on
ꢁꢂꢁSb were performed by a phase-coherent pulsed spec-
trometer using the powder sample. The magnetization
was measured with a SQUID magnetometer.
*Corresponding author. Tel.: #81-75-753-2943; fax: #81-
75-753-6804; e-mail: f52017@sakura.kudpc.kyoto-u.ac.jp.
0921-4526/99/$ — see front matter ( 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 7 0 9 - 1

160
K. Hashi et al. / Physica B 259—261 (1999) 159—160
Fig. 3. External magnetic field dependence of the FWHM of
NMR spectra in the ordered and the paramagnetic states. Solid
lines are guide for eyes.
Fig. 3 shows the external magnetic field dependence of
the FWHM in the ordered and the paramagnetic states
at 4.2 and 6 K, respectively. The FWHM in the ordered
state is proportional to the external field with a slope
which is steeper than that in the paramagnetic state. The
FWHM at the extrapolated external magnetic field of
zero in the ordered state are about 130 Oe larger than
that in the paramagnetic state. It seems that this addi-
tional broadening at the extrapolated field of zero comes
from the ordered magnetic moment. The magnitude of
Fig. 1. Temperature dependence of the NMR spectra around
5 K in YbSb C2.
the ordered moment is estimated to be about 0.07l from
the additional broadening of 130 Oe and the calculated
dipole field of 1.825 kOe/l assuming the type III
magnetic structure. The ordering of this extremely re-
duced moment can explain why the transition around
5 K which is observed by the Mossbauer spectroscopy
mea-surements had not been observed by the neutron
diffraction experiments. Because the neutron diffraction
experiments exclude the existence of only the antifer-
romagnetic ordering with magnetic moment larger than
Fig. 2. Magnetic phase diagram of YbSb. Inset shows the tem-
perature dependence of the magnetization under the external
magnetic field of 3 T.
0.1l .
Fig. 1 shows the temperature dependence of the NMR
spectra around 5 K in YbSb C2. A distinct broadening
of the NMR spectrum around 5 K was observed in YbSb
C2. This clearly shows the presence of the phase
transition in YbSb C2 as in YbSb C1. The presence of
the phase transition around 5 K in YbSb C2 is also
confirmed by a small peak in the temperature depend-
In conclusion, the presence of the phase transition
about 5 K in YbSb was confirmed in our sample of YbSb
C2 as well as in the ETH sample of YbSb C1. This phase
transition in YbSb C2 was observed more clearly than
that in YbSb C1 in the measurements of the magnetiz-
ation and the phase diagram was obtained. The details
will be published elsewhere.
ence of the spin-lattice relaxation rate 1/¹ . The temper-
ꢁ
ature dependence of the magnetization under the
magnetic field of 3 T is shown in the inset of Fig. 2. There
is a small bend which was not observed clearly in YbSb
C1. The similar bend was observed in each sequence
under various magnetic fields. Fig. 2 shows the magnetic
phase diagram obtained from these bends. The transition
temperature increases with increasing the external mag-
netic field. This transition has also been observed in the
specific heat measurements up to 10 T [4]. In order to
clarify the magnetic properties of the phase transition,
the external magnetic field dependence of the FWHM in
the ordered and the paramagnetic states were measured.
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