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Short Notes phys. stat. sol. (a) 43, K185 (1978) Subject classification: 18.2; 21.1

K185

Institute of Solid State Physics, Academy of Sciences of the USSR, Chernogolovka Magnetization of Co-H Solid Solutions BY V.G. THIESSEN, V.E.ANTONOV, 1:T. BELASH, B.K. PONOMAREV, and E .G. PONYATOVSKII Since a considerable number of hydrogen-containing phases on the basis of transition metals of the groups VI to VIII of the periodic table was obtained only in recent years (see review papers /1, 2/), works dealing with their physical properties

are still rare. As to the magnetic properties, it was found that the hydride of antiferromagnetic chromium is paramagnetic down to low temperatures /3/; the hydride of antiferromagnetic manganese is ferromagnetic /4/; the dissolving of hydrogen in

ferromagnetic nickel lowers its Curie temperature /5, 6/, and at room temperature nickel hydride is paramagnetic /7/; hydrogenation of strong paramagnetic palladium beyond H to the metal atomic ratio n tivity /8/. The solubility of hydrogen in the low-temperature h.c. p. allotropic modification of cobalt was shown to increase steadily with pressure of molecular hydrogen, reaching n SO. 5 at P = 65 kbar and T w 500 K /9/. In the present paper the HZ magnetization of Co-H solid solutions was measured at P = 1 at in a pulsed magnetic field up to 50 kOe in the temperature range
(80 to 220)K, the pulse duration being
0.2 mm thick at PHz& 60 kbar and

*

0.8 leads to the appearance of superconduc-

0.01 s. The specimens were prepared by quenching down to 260 K after the hydro-

genation of electrolytically pure cobalt plates

T = 520 K for some hours. Note, that at normal pressure Co-H samples thus obtained are kinetically unstable in regard to the desintegration into the metal and molecular hydrogen at temperatures above 260 K /9/. The methods of Co-H sample preparation

-

and their chemical analysis (with an accuracy of about 3%) are described in /9/, and the magnetic measurement techniques in /lo, 11/.

The temperature dependence d(T) of the spontaneous magnetization of our Co and Co-H specimens is weak in the temperature range investigated; and the changings in d (T) are within the limits of the experimental error 6d/b
&

0.05. The value of


K186

physica status solidi (a) 48 Fig. 1. Spontaneous magnetization d at T = 0 K of Co-H solid solutions as a function of 'the H to metal atomic ratio n. The broken line shows the d (n) 0 dependence in the rigid band approximation

lfjq
9
75

9

*

14
\
'\

130

07

02

03

01
n-

05

lacf/aTI is known to decrease with decreasing temperature. So, we assumed the mean value of d
6 at absolute zero.
0

at 80 d T

5 220 K to be equal to the spontaneous magnetization au /an
0

Experimental results are presented in Fig. 1. The broken line shows the linear dependence d (n) with a slope
0

/Co atom ()L is the Bohr magneton). B B This dependence is given by a rigid band approximation under the assumptions that
=

r

-1

J.L

(i) cobalt is a strong itinerant ferromagnet, and (ii) hydrogen, on dissolving into cobalt, transfers its electron to the conduction band of the metal /12/. As one can

see from Fig. 1, the slope of the experimental curve d (n) differs noticeably from
0

the value predicted by the rigid band model even at low hydrogen content in cobalt: ~ 0 . 6 /Co atom. Thus a study of the u (n) dependence shows that p B 0 n=O hydrogen being dissolved in cobalt strongly deforms its band structure. It is worth n pointing out that direct quantum mechanical calculations of the band structures of hydrides of several 3d- and 4d-elements /13 to 15/ also show that the rigid band approximation and, in particular, the "protonic" and llanionic" models are unsatisfactory for describing of physical properties of these compounds. The authors thank I.A. Potapova and A.I. Amelin for valuable assistance ren-. dered in conducting the experiments. References /I/ E.G. PONYATOVSKII, V.E. ANTONOV, and I.T. BELASH, Proc. Internat. Conf. Quantum Crystals, Fort Collins (USA), August 1977.
/2/ E.G. PONYATOVSKII, V.E. ANTONOV, and I.T. BELASH, Izv. Akad. Nauk

as/a

I

SSSR, Ser. neorg. Mater.

14, No.

9 (1978), in the press.

/3/ H.R. KHAN and'C. J. RAUB, J. less-common Metals 49, 339 (1976).
/4/ I.T. BELASH, B.K. PONOMAREV, V.G. THIESSEN, N.S. AFONIKOVA,

V.SH. SHEKHTMAN, and E.G. PONYATOVSKII, Fiz. tverd. Tela (1978).

20,

422


Short Notes

K187

/5/ E.G. PONYATOVSKII, V.E. ANTONOV, and I.T. BELASH, Dokl. Akad. Nauk SSSR

229,

391 (1975).

/6/ V.E. ANTONOV, I.T. BELASH, and E.G. PONATOVSKII, Dokl. Akad. Nauk SSSR

233,

1114 (1977).

/7/ L. KOZ-EOWSKI and S. KUBIAK, phys. stat. sol.
/8/ T. SKOSKIEWICZ, phys. stat. sol. (a)

3,

K177 (1963).

1'1,K123

(1972).

/9/ I.T. BELASH, V.E. ANTONOV, and E.G. PONYATOVSKII, Dokl. Akad. Nauk SSSR

235,

128 (1977).

/lo/

V.E. ANTONOV, I.T. BELASH, B.K. PONOMAREV, E.G. PONYATOVSKII, and V.G. THIESSEN, Fiz. tverd. TelaLO, 418 (1978).

/11/ L. JACOBS and P. LAWRENCE, Rev sci. Instrum. 28, 713 (1958).

/12/ J. FRIEDEL, Ber. Bunsenges. phys. Chem.
/13/ A.C. SWITENDICK, Solid State Commun.

76,

838 (1972).

S,

1463 (1970).

/14/ A .C. SWITENDICK, Ber. Bunsenges. phys. Chem.

3, 536

(1972).

/15/ N. KULIKOV, A. ZVONKOV, and 0. NLALYUCHKOV, Proc. 2nd Internat. Congr. Hydrogen in Metals, Paris, June 1977 (2A1). (Received May 12, 1978)