- Email: [email protected]
Comparison of TmS with TmSe and CeAl2
433
Journal of Magnetism and Magnetic Materials 31-34 (1983) 433-434 COMPARISON J. P E Y R A R D ,
OF TinS WITH TmSe AND CeAI J. F L O U Q U E T ,
P. H A E N , F. L A P I E R R E ,
Y. L A S S A I L L Y , F. H O T Z B E R G
*
Centre de Recherches sur les Trbs Basses Tempbratures, CNRS, BP 166 X, 38042 Grenoble-Cedex, France a n d C. V E T T I E R lnstitut Laue-Langevin, BP 156 X, 38042 Grenoble-Cedex, France
Neutron diffraction, susceptibility and specific heat (C) measurements on single crystals of TmS, with TN = 5.17 K, are reported. In addition to the classical y T + fiT 3 terms, C contains an extra contribution above TN which can be fitted by a triplet ground state Schottky-like anomaly. Comparisons are made with TmSe and CeAI 2,
|
In TINS, the Tin ions are in a trivalent state, as proved by optical measurements [1], although the effective moment, Pete-- 7 # B / T m [2,3], deduced from the high temperature Curie-Weiss susceptibility, x ( T ) , is lower than the free ion value ( = 7.56#B/Tm ). TmS shows a metallic resistivity with a K o n d o like increase down to - 15 K [4]. Therefore it has been classified as a K o n d o lattice compound, like the classical example CeAlz, with the difference that in TmS the number of itinerant electrons is just equal to the number of Tm ions. As CeAI 2, TmS exhibits antiferromagnetic (AF) order at low temperatures. Values of T N, 5.18 K [2] and 6.45 K [4], as deduced from the peak of x ( T ) , have been reported. On the other hand, neutron diffraction experiments [3] revealed the appearance of A F order below 8.9 K, i.e. at temperatures much higher than T~ - 5 K (deduced from x ( T ) for the same sample). Satellites corresponding to an almost type II sinusoidally modulated structure were observed together with diffuse streaks of scattering. These discrepancies between the T N values remained unexplained. Other important problems exist in TmS such as the evaluation of the linear term of the specific heat on both sides of the A F transition and the exact determination of the crystal field splitting. Finally, from both experimental and theoretical points of view, a comparison between TmS and TmSe appears to be of great interest. We have performed new neutron diffraction, susceptibility and specific heat measurements down to 1.4 K on single crystals cleaved from two different ingots. Apart from a small difference in the values of T~ 5.27 K and 5.17 K), the data are very similar for the two sets of crystals and here we shall report only data relative to the second set. The neutron diffraction experiments were performed on the 4-circle diffractometer D I 0 at the ILL. Our * Permanent address: IBM T.J. Watson Research Center, Yorktown Heights, NY 10598, USA. 0304-8853/83/0000-0000/$03.00
,
i
171o ~O~
Tm
I'mS
g 8 g~
8~
0,51
o
50
o o°
d?
4~ "7____/ 2~ QI
0
2
4
T(K) G
0
40
,
J
,
J
2
4
6
T (K)
10
Fig. ]. (a) (left hand side). Normalized neutron intensities versus T for a single crystal of TmS. (b) (Right hand side). Susceptibility x(T) and specific heat C(T) in the vicinity of Tr~ for another single crystal cleaved from the same ingot.
results show that the magnetic structure is sinusoidally modulated with a wavevector ( ½ - r , ½ + ~ , - ½ ) as previously reported [3], but with z = 0.078 instead 0.08. However, contrary to the data of ref. [3], no diffuse features in the scattering pattern have been observed. The variation of the magnetic intensity versus T (fig. la) yields T N = 5.17 K. Exactly the same value is deduced from x ( T ) (inflexion point in the upper curve on fig. lb) and from the peak of the specific heat, C(T) (lower curve on fig. lb). We have analysed C ( T ) by the same procedure as that used for TmSe [5]. The plot in fig. 2 of C / T versus T 2 up to 20 K shows that, above TN, there is an extra contribution C~xt to C(T) together with the linear electronic term yHT T and the phonon term flphT3. Assuming flph equal to that of LaS [2], i.e. flph=0"185 m J / m o l / K 4, a good fit of C(T) can be achieved above T N (fig. 2) with VnT = 340 m J / m o l / K 2 and with Cext in the form of a two level Schottky-like anomaly with a splitting energy A = 25 K and a degeneracy ratio g J g o = 0.8. For TmSe the corresponding terms were YHT = 350 m J / m o l / K 2, A = 80 K and gl/go = 3. In TmS the
© 1983 N o r t h - H o l l a n d
Journal of Magnetism and Magnetic Materials 31-34 (1983) 433-434 COMPARISON J. P E Y R A R D ,
OF TinS WITH TmSe AND CeAI J. F L O U Q U E T ,
P. H A E N , F. L A P I E R R E ,
Y. L A S S A I L L Y , F. H O T Z B E R G
*
Centre de Recherches sur les Trbs Basses Tempbratures, CNRS, BP 166 X, 38042 Grenoble-Cedex, France a n d C. V E T T I E R lnstitut Laue-Langevin, BP 156 X, 38042 Grenoble-Cedex, France
Neutron diffraction, susceptibility and specific heat (C) measurements on single crystals of TmS, with TN = 5.17 K, are reported. In addition to the classical y T + fiT 3 terms, C contains an extra contribution above TN which can be fitted by a triplet ground state Schottky-like anomaly. Comparisons are made with TmSe and CeAI 2,
|
In TINS, the Tin ions are in a trivalent state, as proved by optical measurements [1], although the effective moment, Pete-- 7 # B / T m [2,3], deduced from the high temperature Curie-Weiss susceptibility, x ( T ) , is lower than the free ion value ( = 7.56#B/Tm ). TmS shows a metallic resistivity with a K o n d o like increase down to - 15 K [4]. Therefore it has been classified as a K o n d o lattice compound, like the classical example CeAlz, with the difference that in TmS the number of itinerant electrons is just equal to the number of Tm ions. As CeAI 2, TmS exhibits antiferromagnetic (AF) order at low temperatures. Values of T N, 5.18 K [2] and 6.45 K [4], as deduced from the peak of x ( T ) , have been reported. On the other hand, neutron diffraction experiments [3] revealed the appearance of A F order below 8.9 K, i.e. at temperatures much higher than T~ - 5 K (deduced from x ( T ) for the same sample). Satellites corresponding to an almost type II sinusoidally modulated structure were observed together with diffuse streaks of scattering. These discrepancies between the T N values remained unexplained. Other important problems exist in TmS such as the evaluation of the linear term of the specific heat on both sides of the A F transition and the exact determination of the crystal field splitting. Finally, from both experimental and theoretical points of view, a comparison between TmS and TmSe appears to be of great interest. We have performed new neutron diffraction, susceptibility and specific heat measurements down to 1.4 K on single crystals cleaved from two different ingots. Apart from a small difference in the values of T~ 5.27 K and 5.17 K), the data are very similar for the two sets of crystals and here we shall report only data relative to the second set. The neutron diffraction experiments were performed on the 4-circle diffractometer D I 0 at the ILL. Our * Permanent address: IBM T.J. Watson Research Center, Yorktown Heights, NY 10598, USA. 0304-8853/83/0000-0000/$03.00
,
i
171o ~O~
Tm
I'mS
g 8 g~
8~
0,51
o
50
o o°
d?
4~ "7____/ 2~ QI
0
2
4
T(K) G
0
40
,
J
,
J
2
4
6
T (K)
10
Fig. ]. (a) (left hand side). Normalized neutron intensities versus T for a single crystal of TmS. (b) (Right hand side). Susceptibility x(T) and specific heat C(T) in the vicinity of Tr~ for another single crystal cleaved from the same ingot.
results show that the magnetic structure is sinusoidally modulated with a wavevector ( ½ - r , ½ + ~ , - ½ ) as previously reported [3], but with z = 0.078 instead 0.08. However, contrary to the data of ref. [3], no diffuse features in the scattering pattern have been observed. The variation of the magnetic intensity versus T (fig. la) yields T N = 5.17 K. Exactly the same value is deduced from x ( T ) (inflexion point in the upper curve on fig. lb) and from the peak of the specific heat, C(T) (lower curve on fig. lb). We have analysed C ( T ) by the same procedure as that used for TmSe [5]. The plot in fig. 2 of C / T versus T 2 up to 20 K shows that, above TN, there is an extra contribution C~xt to C(T) together with the linear electronic term yHT T and the phonon term flphT3. Assuming flph equal to that of LaS [2], i.e. flph=0"185 m J / m o l / K 4, a good fit of C(T) can be achieved above T N (fig. 2) with VnT = 340 m J / m o l / K 2 and with Cext in the form of a two level Schottky-like anomaly with a splitting energy A = 25 K and a degeneracy ratio g J g o = 0.8. For TmSe the corresponding terms were YHT = 350 m J / m o l / K 2, A = 80 K and gl/go = 3. In TmS the
© 1983 N o r t h - H o l l a n d