PRESSURE DEPENDENCE OF THE NÉEL TEMPERATURE AND LATTICE PARAMETER OF AN ORDERED ALLOY MnPd3

HAL Id: jpa-00228992

https://hal.archives-ouvertes.fr/jpa-00228992

Submitted on 1 Jan 1988

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

PRESSURE DEPENDENCE OF THE NÉEL

TEMPERATURE AND LATTICE PARAMETER OF

AN ORDERED ALLOY MnPd3

H. Yasui, T. Kaneko, S. Abe, H. Yoshida, K. Kamigaki

To cite this version:

JOURNAL DE PHYSIQUE

Colloque C8, Suppl6ment au no 12, Tome 49, dkembre 1988

PRESSURE DEPENDENCE OF THE NEEL

TEMPERATURE AND LATTICE

PARAMETER OF AN ORDERED ALLOY MnPd3

H. Yasui, T. Kaneko, S. Abe, H. Yoshida and K. Kamigaki

The Institute for Materials Research, Tohoku University, Katahira, Sendai, 980, Japan

Abstract. - The ordered alloy MnPd3 is an antiferromagnet with the Nkel temperature TN = 195 K. The pressure dependence of TN and lattice parameter was measured. The pressure derivative of TN and the volume compressibility were obtained to be 0.2 K/kbar and 1.3 x

low3

kbar-l, respectively.

There are many ferro- or antiferromagnetic or- dered Mn alloys, in which the main carriers of mag- netic moments are Mn atoms. The occurrence mecha- nism of ferro- and antiferrornagnetism in these ordered Mn alloys has been discussed in terms of the depen- dence of exchange interaction on the interatomic dis- tance between Mn atoms [I-41. In general, the pressure dependence of magnetic transition temperature gives the significant information of the distance dependence of exchange interaction. Many reports have been al- ready published about the pressure effect on the Curie temperature (Tc) of ferromagnetic Mn alloys [5, 61. On the other hand, there are few investigations on the pressure dependence of the N6el temperature (TN) of antiferromagnetic alloys. Thus in order t o clarify the whole feuture of the interaction curve for the Mn al- loys, it is worth while to examine the pressure effect on TN of the antiferromagnetic Mn alloys and compounds. The ordered alloy MnPd3 has the crystal structure of a one-dimensional long-period superlattice based on the Cu3Au-type order with period antiphase do- mains [7]. It has the collinear antiferromagnetic structure with p ~ , , = 4 pg, where the Mn-Mn nearest- neighbor(n.n.) and next-nearest-neighbor(n.n.n.) in- teractions are ferromagnetic and antiferromagnetic, re- spectively [8]. The NBel temperature is strongly depen- dent on the degree of atomic order and decreases with decreasing atomic order 191.

In this paper, the temperature variations of mag- netic susceptibility and electrical resistivity, the ther- mal expansion and the pressure effect on the NBel tem- perature were measured for the ordered alloy MnPds. The specimen was prepared by arc-melting the ele- ments of appropriate quantities under a purified argon gas. The ingot was annealed for 3 days at each tem- perature of 900 OC, 800 OC, 700 OC, 600 OC and 500 OC and finally for 10 days at 450 OC. The X-ray diffraction study showed that the prepared specimen is a single phase and has the lattice parameter a = 3.903

A.

But, the supperlattice lines were not detected owing to very small intensities.

Figure 1 shows the temperature dependence of mag- netic susceptibility for annealed specimen. As temper-

Fig. 1. - Temperature dependence of the magnetic suscep tibility.

ature increases, the susceptibility has a maximum at 195 K (TN)

.

According t o reference [9], this peak tem- perature in the susceptibility corresponds to the most ordered alloy case and the atomic longrange order pa- rameter of the annealed specimen is estimated to be 0.90 f 0.05.

Figure 2 shows the temperature variation of electri- cal resistivity for unannealed and annealed specimens. As temperature increases, the resistivity of the unan- nealed specimen increases monotonously and does not

MnPdg

Ro: RESISTANCE AT R O O M TEMPERATURE

'

TN

/'

1 QUENCHED 2 A N N E A L E D

50 100 150 200 250 300

T E M P E R A T U R E C K )

Fig. 2.

-

Temperature dependence of electrical resistivity.

C8 - 178 JOURNAL DE PHYSIQUE show any anomaly. But the temperature coefficient of

the resistivity is observed to change around the maxi- mum temperature in the susceptibility for the annealed specimen.

The pressure dependence of TN was determined by measuring the temperature variations of resistivity un- der various pressures. Figure 3 shows the temperature variations of the resistivity under normal pressure and 5.9 kbar. TN defined as shown in the figure increases with pressure. The pressure derivative ( ~ T N / d P ) is obtained t o be 0.2 K/kbar.

The pressure variation of the lattice parameter a was

measured by a high-pressure X-ray diffraction using a cubic anvil-type apparatus at room temperature. The result is shown in figure 4, in which a decreases linearly

X

-

W

170 180 190 2 0 0 210 220 TEMPERATURE CK)

Fig. 3.

-

Temperature dependence of electrical resistivities under normal pressure and 5.9 kbar.

.015 -

-

M* a0 =3.90(A)

-

Compressibilty ~ = 1 . 3 ~ 1 0 - ~ ( ~ b a r - l )

Fig. 4.

-

Pressure dependence of lattice parameter.

with pressure. The obtained volume compressibility

nv is 1.3

x

lov3

kbar-l. Using the value of dTN

/

d P and tcvt the lattice parameter dependence of TN is ob- tained to be dTN

/

da = -1.2

x

i o 2 ~ / A .

The thermal expansion was also measured for the ordered alloy MnPds. The significant anomaly was not detected a t TN within experimental accuracy. This result is related t o that pressure dependence of TN is very small.

It is considered that Mn in the ordered alloy MnPds has a local moment in a usual sense [lo, 111. Accord- ing to the interaction curve between the local magnetic moments by Endoh et al. [4], the exchange integral ( J ) tends t o change the sign from positive to negative when Mn-Mn distance is

-

4 A. In the case of MnPds, Mn- Mn n.n. and n.n.n. distance are 3.90

A

and 4.78

A,

respectively. Therefore, the signs of exchange integral (J,.,. and J,.,.,.) are consistent with those expected from the interaction curve by Endoh et al. And, J,.,.

increases but (J,.,.,I decreases with an application of pressure from the curve. Since TN is in proportion to 5Jn.n.+41Jn.n.n1,dJn.n./dPanddIJn.n.n.I/dPtend to cancel out each other. The small values of ~ T N

/

d P obtained in this experiment is consistent with that de- duced from the interaction curve.

[I] Guillaud, C., Thesis, Strasbourg (1943). [2] Castellitz, L., 2. Metallkd. 46 (1955) 198. [3] Sato, H., J. Appl. Phys. 31 (1960) 327s. [4] Endoh, Y. and Ishikawa, Y., Solid State Phys. 5

(1970) 245.

[5] Shirakawa, K., Kanomata, T. and Kaneko, T., J.

Magn. Magn. Mater. 70 (1987) 421.

[6] Shirakawa, K., Kanomata, T. and Kaneko, T., J.

Magn. Magn. Mater. 65 (1987) 76.

[7] Cable, J. W., Wollan, E. O., Koehler, W. C. and Shild, H. R., Phys. Rev. 128 (1962) 2118. [8] Kren, E. and Kadar, G., Phys. Lett. A 29 (1969)

340.

[9] Kren, E., Kadar, G. and Pal, L., J. Appl. Phys.

41 (1970) 941.

[lo] Campbell, I. A., J. Phys. C 1 (1968) 687. [ l l ] Ziebeck, K. R. A., Webster, P. J., Brown, P. J.

and Bland, J. A. C., J. Magn. Magn. Mater. 24