The influence of Co substitution for Fe on the lattice parameters, ordering temperature, saturation magnetisation, spin-reorientation temperature, and first-order magnetisation process (FOMP) of HoFe11−xCoxTi (x=0.3, 0.7, 1, 3, 5, 7, 9, 11) compounds is investigated. The tetragonal crystal structure of the parent HoFe11Ti does not change upon Co substitution, but the lattice parameters a and c decrease monotonically with the increase of Co content. The increase of x in HoFe11−xCoxTi compounds has a beneficial effect in improving the Curie temperature from 513 K in HoFe11Ti to 983 K in HoCo11Ti compound. The highest saturation magnetisation was observed in the compound with x=3 at all measured temperatures. In HoFe11−xCoxTi compounds, with x=0, 1, 3, 5, 7 a FOMP of type II occurs at fields less than 2 T and below 100 K. In HoFe2Co9Ti and HoCo11Ti compounds spin reorientations are observed at TSR=260 and 273 K, respectively.

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