Magnetostructural phase transitions and magnetocaloric effect in Mn(As,P) compounds and their composites

Abstract The magnetostructural phase transition in Mn(As,P) compounds was studied by a combination of X-ray diffraction on single crystals and by the magnetisation measurements. The mentioned transition is accompanied by anisotropic deformation of the crystal lattice, magnetisation hopping and heat evolving due to a large magnetocaloric effect (MCE). It is shown that this transition is a transformation from the hexagonal ferromagnetic to the orthorhombic paramagnetic phase at heating above the Curie temperature (T C ). The values of the magnetic and lattice entropy changes at phase transition are obtained and the adiabatic temperature change is estimated in the frame of Clapeyron-Clausius relations. It is found that the MCE in the magnetic field 140 kOe reaches the value of 13.5 K. It is shown that a superparamagnetic structure (as a conglomerate of microscale areas) is formed above Curie temperature in zero magnetic field. On the other hand at the temperatures above the T C the ferromagnetic state is induced by magnetic fields exceeding the certain critical value H cr while the above-mentioned superparamagnetic state is destroyed by the same magnetic fields. The magnetic properties of the bulk Mn(As,P) and the polymeric composite based on Mn(As,P) compound are compared.