Controllable isotropic thermal expansion in series of designed magnetocaloric materials HoCo₂Mn_x (x = 0–1.0)

We detected a crossover from negative to positive thermal expansion with increasing Mn in HoCo Mn below the Curie temperature through high quality neutron diffraction measurements from 5 K to 400 K. Almost isotropic zero thermal expansion with coefficient of thermal expansion α = −4.894 × 10 /K was achieved over a large range of temperature from 5 K to T = 225 K in the compound HoCo Mn . While the addition of manganese was shown to change the temperature dependence of the lattice, it was also noted that the Curie temperature rose significantly from 88 K in HoCo to 253 K in HoCo Mn providing a hope for a room temperature transition in similar doping series materials. 2 x l C 2 0.5 2 2 −7