Journal of Magnetism and Magnetic Materials 70 (1987) 345-346 345 North-Holland, Amsterdam MAGNETIC PROPERTIES OF (GdxY t_ x)Co4B COMPOUNDS E. BURZO and M. URSU Central Institute of Physics, P.O. Box MG-6, Bucharest, Romania The magnetic properties of (Gd,Y I ~)Co4B compounds were studied in the temperature range 4.2-1000 K. The compounds with x/> 0.2 are ferrimagnetically ordered. The mean cobalt moment increases from 0.67~, in YCo4B to 0.98p.~ in GdCo4B. The temperature dependence of the reciprocal susceptibilities for compounds with x >/0.2 may be described by a hyperbolic law of N6el-type. The RCo 4B compounds, where R is a rare earth or yttrium, crystallize in CeC%B-type structure [1]. This is obtained by ordered substitutions of cobalt by boron in every second layer of CaCu 5- structure. The cobalt atoms occupy two types of sites. The magnetic properties of RCo4B com- pounds were reported by Oesterreicher et al. [2] and Pedziwiatr et al. [3]. The GdCo4B is ferri- magnetically ordered while in case of YCo4B a ferromagnetic ordering is evidenced. In order to obtain information of the magnetic behaviour of cobalt in compounds with CeC%B- type structure, we studied the (Gd~YI_~)Co4B system. In this system the electron concentration is not modified by the gradual substitution of yttrium by gadolinium. Thus, the variation of cobalt moment may be attributed only to the changes in the magnetic interactions involving the cobalt atoms. The (Gd,Y 1 .x)Co4B compounds were prepared by melting the constituent elements in a water- cooled copper boat by rf heating under argon atmosphere. The compounds were annealed for one week at 900°C and then rapidly cooled to room temperature. The X-ray analysis showed the presence of only one phase. Magnetic measure- ments were performed by means of several types of equipment, in the temperature range 4.2-1000 K. In analysing the data we use a two sublattice model corresponding to gadolinium and cobalt magnetizations. The composition dependence of the magnetiza- tions is plotted in fig. la. The magnetizations of the gadolinium and cobalt sublattices are com- pensated for x = 0.47. Supposing that the mag- netic moment of gadolinium is 7/~B, we determined the cobalt contribution to the magnetization - fig. lb. The cobalt moment is dependent on composi- tion increasing from 0.67/x B (x = 0) up to 0.98/~ B (x = 1.0). The ferrimagnetic ordering evidenced by saturation studies for compounds having x >~ 0.2 is also proved by magnetic measurements above the Curie points. As seen in fig. 2, the inverse of the paramagnetic susceptibility as function of tem- perature follows a hyperbolic law of N6el-type, which can be expressed in the form [4] --1 1 l l X =Xo +TC -o(T-O) (1) We denoted by C the Curie constant and by X0, o and 0 the parameters which are functions of the molecular field coefficients. According to the addition law of susceptibilities and supposing that the Curie constant of z 25 _>'~ N 02 04 06 08 1.0 ~ COMPOSfTION { x) The composition dependence of the saturation magneti- (a), cobalt magnetization (b) and the effective cobalt moments (c). Fig. 1. zation 0304-8853/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)