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Submitted on 1 Jan 1988
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EFFECT OF PRESSURE ON THE MAGNETIC
TRANSITION TEMPERATURES IN (Cr1-xRhx)3 Te4
S. Ohta, T. Kaneko, H. Yoshida, S. Anzai, T. Kanomata
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Suppl6ment au no 12, Tome 49, d6cembre 1988
EFFECT OF PRESSURE ON THE MAGNETIC TRANSITION TEMPERATURES IN
( C r l - z R h , ) ~ Te4
S. Ohta (I), T. Kaneko (2), H. Yoshida (2), S. Anzai (3) and T. Kanomata (4)
(I) Hachinohe Institute of Technology, Hachinohe, Japan
(2) The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai, Japan
(3) Keio University, Yokohama, Japan
(4) Tohoku Gakuin University, Tagajo, Japan
Abstract.
-
The pressure derivatives of the Curie temperature and the spin canted one in x = 0.17 are - (4.1 f 0.3) and+
(2.3 f 0.4) in units of Klkbar, respectively. Those of the transition temperature between the canted ferromagnetic and paramagnetic phases in x = 0.17 (high pressure) and 0.33, respectively, are-
(4.1 f 0.6) and-
(3.1 f 0.2) in units of K/kbar.The ferromagnetic compound CrsTe4 is charac- terized by a canted ferromagnetic (CF)-ferromagnetic (F) transition at a temperature (Tt) [I] and a large negative pressure derivative of the Curie temperature (T,) (- (5.9
f
0.1) K/kbar) [2]. In the magnetically diluted system (Crl-xRhx)3 Ted, Tt increases and Tc decreases as x increases [3]. Both Tt and Tc combine at a point (x = 0.21 f 0.03, T = (165 f 5) K). Whenx further increases, only a CF-paramagnetic transi- tion is observed a t a temperature (TcF). These be- haviours are explained with the aidependence of the virtual exchange integrals. In this paper, Tc and Tt in (C~0.83Rh0.17) 3 Te4 and TCF in (Cr0.67rth0.33) 3 Te4 are
investigated under pressure as the typical examples of the magnetic transitions in (Crl-,Rh,) Te4.
The powder samples were prepared with the same procedure [4] reported previously. The measurements of the temperature (T) dependences of magnetic per- meability (p) at hydrostatic pressure (P) were carried out by using a piston-cylinder type apparatus on heat- ing runs.
Figure 1 shows the temperature dependence of p for (Cro.s~Rh0.17)3 Te4 at various pressures. At normal pressure, p exhibits a sharp peak at T = 170 K and a discontinuity in d p
/
d T a t T = 110 K. By comparing this curve with the magnetization (a) us. T curve ofx = 0.17 [3], Tc is assigned as the intersection of the high temperature-side of the peak and the higher tem- perature range, and Tt, the temperature of the discon- tinuity in d p
/
d T as shown in figure 1. As P increases, Tc decreases and Tt increases. Above P = 10.9 kbar, the discontinuity in d p/
d T at Tt gets blurred and p exhibits only a sharp peak whose magnitude decreases with increasing P. As described below (Fig. 3), this type of peak in p is also observed in x = 0.33 just be- low TCF determined on the a us. T curve [3] a t normal pressure. The peak is regarded as the presence of the CF-paramagnetic transition. Then, TCF is determined with the same manner t o that for T,. As seen in fig- ure 2, Tc and Tt of x = 0.17 decreases and increases in70 120 170 220 270 320 TEMPERATURE
,
KFig. 1. - Temperature dependence of permeability for (Cr0.83Rh~.~~) Te4 at various pressures.
the pressure derivatives dTc
/
d P =-
(4.1 f 0.3) and dTt/
d P =+
(2.3 f 0.4) in units of K/kbar, respec- tively. Above a triple point ( P = (8.6f
0.3) kbar, T = (143 f 3) K), Tc andTt
combine to make a transition line with T C ~ whose pressure derivative is d T c ~/
d P =-
(4.1 f 0.6) K/kbar. Figure 3 shows the temperature dependence of p for (Cr0.67R.ho.33) 3 Te4at various pressures. At normal pressure, p exhibits only a sharp peak whose magnitude decreases with in- creasing P. This thermal variation of p has the same feature as the case of x = 0.17 at the higher pressures. As shown in figure 2, TCF decreases with increasing P,
from which the pressure derivative is determined t o be d T c ~
/
d P =-
(3.1f
0.2) K/kbar.It has been pointed out that an enhancement of the contribution of negative exchange integrals in the effec-
C8
- 210
JOURNAL DE PHYSIQUEI I * I I I h 1 I
0 2 4 6 8 10 12 14 16 P , kbor
Fig. 2. - Pressure dependences of the magnetic transition temperatures Tc, Tt and TcF for ( C r 1 - ~ R h ~ ) ~ T e 4 with
z = 0.17 and 0.33.
I I I I I J
70 120 170 220 270 320 TEMPERATURE , K
tive magnetic interactions suppresses Tc and TCF but rises Ttas x increases in (Crl-,Rh,)3 Tea (31. The P
-
T diagram observed in (Cr0.83Rh0.17)~ Ter fairly coincides with the x-
T one [3] when P is linearly scaled tox.
This feature is also supported .with the pressure dependence of TCF in (Cr0.67FLh0.33)~ Ter. It is plausible that the reduction in interatomic distances or the variation in the axial ratio introduced by pres sure takes sides with the antiferromagnetic contribu- tions which compete to the predominant ferromagnetic effective exchange integrals in this system. As a s u p plementary notice, there are some quantitative differ- ences,in dTc/
d P betweenx =
0 and 0.17 and those in d T c ~/
d P between x = 0.17 (high pressure) and 0.33. In order to study these features, a systematic in- vestigation, together with the exchange strictions, over the more wide range of x are now in progress.[l] Bertaut, E.
I?.,
Rault, G., Aleonard, R., Chevre- ton, M. and Jansen, R., J . Phys. h n c e 25 (1964) 582.[2] Ozawa, K., Yoshimi, T., hie, M. and Yanagisawa, S., Phys. Status Solidi (a) 11 (1972) 581. [3] Ohta, S., Fujii, A. and Anzai, S., J . Phys. Soc.
J p n 52 (1983) 1765.
[4] Fujii, A., Ohta, S. and Anzai, S., J p n J . Appl. Phys. 21 (1982) 669.
