L6 Journal of Magnetism and Magnetic Materials 94 (1991) L6-LlO North-Holland zyxwvu Letter zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA to the Editor zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Spin re-orientations in Nd( Fe,Co) & system M. Jurczyk ‘, G.K. Nicolaides and K.V. Rao Dept. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Condensed Matter Physics, The Royal Inst. of Technology, S-100 44 Stockholm, Sweden Received 24 September 1990; in revised form 26 November 1990 The effect of cobalt substitution for iron on the spin re-orientation temperature in tetragonal NdFe,,_,Co,V, alloys (x = 0, 3 and 5) has been investigated using X-ray, magneto-thermogravimetric and ac susceptibility techniques. At room temperature for x = 0, NdFe,,V, exhibits a uniaxial anisotropy, which is found to he strongly modified by cobalt substitution in Nd(Fe,Co),,,V, alloys. In fact, alloys with x = 3 and 5 were found to possess planar anisotropy at this temperature. The NdFe,,,V, and NdFesCosV, compounds were observed to exhibit spin re-orientations at 124 and = 350 K, respectively. These appear to be cone to axial (x = 0) and plane to cone (x = 5) re-orientations with increasing temperature. The NdFe,Q,V, alloy undergoes two spin transitions: one at 210 K and the second at 518 K. The spin structure thus appears to be from a cone to planar, and planar to axial-type, respectively, with increasing temperatures. Thus, the substitution of cobalt in NdFe,,V, causes the spin re-orientation to shift to higher temperatures. 1. Introduction Ternary intermetallic rare earth-(iron,cobalt)- vanadium compounds constitute a new group of alloys which crystallize in the ThMn,, type struc- ture (space group 14/mmm). These alloys are of current scientific and technological interest [l-3] due to their potential for application as hard mag- netic materials [2,4,5]. Properties of substituted 1-12 type compounds, RFe,,_,T, with T = Al, Si, Ti, Cr, Mn, MO, W [1,6] and Re [7,8] have already been reported. Several of these materials have been found to exhibit an intrinsic magnetic spin re-orientation at finite temperatures which, therefore, limits their potential applicability to specific temperature ranges. In the ThMn,, structure, rare earth atoms with a positive second order Stevens factor ((Ye > 0) [e.g. Sm, Er, Tm and Yb], exhibit a preference for magnetization along the c-axis, whereas rare earth elements of cxJ < 0 [e.g. Nd, Tb, Dy and Ho], prefer a non-axial magnetization. On the other ’ Permanent address: Institute of Molecular Physics, Polish Academy of Sciences, 60-179 Poznah, Poland. hand, iron and cobalt sublattices favour uniaxial and planar anisotropies, respectively. It is well known that whenever the 4f sublattice and the 3d anisotropies favour different directions, spin re- orientations are likely to occur [9,10]. There are many reports [9-111 of spin re-orientation phe- nomena in RFe,,V, (R = Nd, Tb, Dy, Ho and Er) compounds, based on bulk magnetization, ac sus- ceptibility and Miissbauer measurements. The pre- sent work deals with the magnetic behavior of NdFe,,_,Co,V, alloys, with x = 0, 3 and 5, in the temperature range 4.2-1200 K. The consequences of substituting iron with cobalt _on the structure and on the Curie and spin re-orientation tempera- tures are reported. 2. Experimental In the present work NdFe,,_,Co,V, (x = 0, 3 and 5) compounds were prepared by induction melting high purity constituents in a water-cooled copper boat under an argon atmosphere. The in- gots were annealed in vacuum at zyxwvutsrqponmlkj T = 870°C for two weeks and then rapidly cooled to room tem- 0304-8853/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)