PRESSURE-INDUCED TRANSITIONS IN INTERMETALLIC COMPOUNDS Mn3Ga1-xAlxC (x ≤ 0.004)

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PRESSURE-INDUCED TRANSITIONS IN

INTERMETALLIC COMPOUNDS Mn3Ga1-xAlxC (x

≤ 0.004)

T. Kaneko, H. Yasui, H. Yoshida, T. Kanomata, T. Yagi, K. Shirakawa

To cite this version:

JOURNAL DE PHYSIQUE

Colloque C8, Supplbment au no 12, Tome 49, dkembre 1988

PRESSUREINDUCED TRANSITIONS IN INTERMETALLIC COMPOUNDS

M n 3 G a l - z A l ~ C (a: 10.004)

T. Kaneko (I), H. Yasui (I), H. Yoshida (I), T. Kanomata (2), T. Yagi (3) and K. Shirakawa (4)

(I) Institute for Materials Research, Tohoku University, Katahira, Sendai 980, Japan

(2) Faculty of Engineering, Tohoku Gakuin University, Tagajo, Miyagi 985, Japan

(3) Institute for Solid State Physics, University of Tokyo, Tokyo 106, Japan

(*) The Research Institute of Electric and Magnetic Alloys, Sendai 982, Japan

Abstract. - The magnetic properties and the pressure effect on the magnetic transition temperatures and the lattice parameter are studied for Mn3Gal-,AI,C (x

<

0.04). On the basis of these results, the relation between the effect of alloying and of pressure on the magnetic transitions of Mn3Gal-,Al,C system is discussed.

The intermetalIic compound MnsGaC has the crystal of a perovskite-type with lattice parameter a = 3.896

A.

The magnetic properties of Mn3GaC show an antiferromagnetic (AF)-ferromagnetic (F) transi- tion at a temperature Tt. The fust-order transition from the AF state to the F one with increase of tem- perature is accompanied by a large discontinuous con- traction of the lattice parameter [I].

Recently, the present authors have studied the ef- fect of pressure on Tt and the Curie temperature Tc of MnsGaC a t pressures up t o 13 kbar. They found that a new intermediate magnetic phase (I) appears a t pres-

sures above 4 kbar [2]. They also studied the magnetic properties of Mn3Gao.g~Alo.02C and MnsGao.gIno.~C and pointed out that the occurrence of the I phase has a close relation to the magnitude of lattice pa- rameter [3]. In this paper, to make clear the relation between the occurrence of the I phase and the lattice parameter, the magnetic properties and the effect of pressure on the magnetic transition temperatures and the lattice parameter were studied for the compound MnsGal-,Al,C (x

5

0.04).

The details of sample preparation are described in reference 121. X-ray diffraction studies showed that the lattice parameter decreases with increase of A1 concen- tration x.

In figure 1 are shown the permeability vs. temper- ature curves for Mn3Gao.97Al0.03C at different pres- sures, where the permeability was measured in an ac magnetic field of about 2 Oe with the frequency of 1 kHz. There appear two kinds of abrupt increases of the permeability in the process of transition from the A F to F phase as temperature increases. This be- havior of the temperature variation of permeability is similar to that of Mn3GaC at pressures above 4 kbar. Therefore, it is considered that the f i s t increase of the permeability at Ttl corresponds to a AF-I tran- sition from the A F phase to the pressure-induced I phase observed in MnjGaC, and the second one a t Tt2 t o the I-F transition. The abrupt decrease-of per-

I ,.,...

--"""

P.2.6 kbar 0 +-.... . .- ... . L n

I

j P ~0.9 k bar +.--

Fig. 1.

-

Permeability us. temperature curves-under hy- drostatic pressures for Mn3Gw.g7Alo.osC.

meability at a higher temperature corresponds to the Curie temperature. As seen in the figure, it is no- ticed that the I phase appears even at normal pres- sure for MnsGao.97Alo.osC and both Ttl and Tt2 de- crease and Tc increases with increasing pressure. In figure 2 are shown the Ttl, Tt2 and T, vs. pressure curves for Mn3Gao.97Alo.o3C1 together with those for MnsGaC. T, increases linearly with pressure and the pressure derivative of Tc is dT,

/

dp = 1.1 K/kbar for hlnsGao.97Alo.osC.

Figure 3 shows the A1 concentration depen- dence of the magnetic transition temperatures for Mn3Gal-,Al,C determined by the magnetic measure- ments. The I phase appears a t normal pressure for d the prepared samples containing Al. Since the lattice

JOURNAL DE PHYSIQUE

Fig. 2.

-

The Curie temperature and the magnetic order-order transition temperatures vs. pressure curves for MnsGaC and Mn3Gao.97Al0.03C. (Tc), (Tti) and (Tt2) represent the magnetic transition temperatures for Mn3Gao.97Alo.03C. 3001 at normal pressure

I

Para 0 - O

-

o/o-

E l

F

Fig. 3.

-

Magnetic phase diagram of Mn3Gal-,Al,C at normal pressures.

parameter decreases with increasing x , Ttl and Tt2 de- crease and Tc increases with decrease of lattice param- eter for Mn3Gal-,Al,C compounds.

The pressure variation of the lattice parameter was measured by using a high pressure X-ray diffractome- ter installed to the cubic anvil press. Figure 4 shows

Fig. 4. - Pressure dependence of volume for MnsGaC.

the pressure change of volume for MnaGaC. The vol- ume decreases linearly with pressure with the volume compressibility Ic, = 0.94 x kbar-'. Using this compressibility the lattice parameter derivatives of Tc, Tt, Ttl and Ttz in unit of

K /

A are obtained to be dTc

/

dp N, -395, dTt

/

da x 2 000, d Z l /

da

x 3 360 and dTtz

/

da x 1 350 for MnsGaC and dTc

/

da rz -890 for Mn3Gao.97Al0.03C.

As mentioned above, the tendency of the lattice parameter dependence of the magnetic transition tem- peratures in Mn3Gal-,Al,C system is similar to that in Mn3GaC under pressure. On the other hand, ac- cording to the result on the compressibility, the lat- tice parameter for x = 0.03 corresponds to that for MnsGaC at about 2 kbar, at which the I phase is not induced. This discrepancy between the effect of alloying and that of pressure on the magnetic transi- tions mean that the effect of alloying is ascribed not only to the decrease of lattice parameter, but to the change of electronic state. To clarify this point fur- ther systematic investigations are now in progress for Mn3Gal-,M,C (M=In, Zn and Sn).

[I] Bouchaud,

J. P.,

Fruchart, R., Guillot, M., Bartholin, H. and Chaisse, F.,

C.

R. Acad. Sci.

Paris 261 (1965) 655.

[2] Kaneko, T., Kanomata, T. and Shirakawa, K., J. Phys. Soc. Jpn 56 (1987) 4047.