Abstract
Isostructural, tetragonal materials were synthesized for the entire composition range ( x = 0 to 14). They were studied by X-ray and magnetometry methods. Magnetization measurements confirm a ferromagnetic arrangement of 3d and Pr magnetic moments and reveal a sharp increase of the Curie temperature with the increase of Co concentration. Saturation magnetization at 295 and 77 K reaches a slight maximum around x = 1 and gradually decreases for higher Co content. Anisotropy fields initially decrease and afterwards increase very quickly as more Co is introduced to the system. A spin reorientation occurs in alloys with x ⩾ 9.5 at temperature higher than 660 K. It marks a transition between uniaxial anisotropy and planar anisotropy. Spin reorientation temperature becomes lower for materials with higher Co content. A discussion of the Curie temperature change is conducted in terms of preferential substitution of Co into 16k 2 sites. The weakening of the exchange interaction between Pr and 3d sublattices, as well as the decreasing Pr-sublattice anisotropy with rising temperature, are considered to be responsible for anisotropy field changes. The interplay between crystal field and exchange field interactions is emphasized. A comparison with the Nd 2Fe 14- x Co x B system is included.
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