Controllable isotropic thermal expansion in series of designed magnetocaloric materials HoCo2Mnx (x = 0–1.0)

Abstract

We detected a crossover from negative to positive thermal expansion with increasing Mn in HoCo2Mnx 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 αl = −4.894 × 10−7/K was achieved over a large range of temperature from 5 K to TC = 225 K in the compound HoCo2Mn0.5. 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 HoCo2 to 253 K in HoCo2Mn providing a hope for a room temperature transition in similar doping series materials.