Structural, magnetic and magnetocaloric properties of HoNi2 and ErNi2 compounds ordered at low temperatures

In this work we report on the structural, magnetic and magnetocaloric properties of polycrystalline HoNi2 and ErNi2 Laves-phase compounds. Powder X-ray diffraction studies at room temperature show that the compounds crystallize in the cubic C15 structure (MgCu2 type). The magnetic measurements reveal that the second-order magnetic phase transition from ferromagnetic to paramagnetic state appears at TC equal 13.5 K for HoNi2 and 6.5 K for ErNi2. Using direct measurements over a wide field range (up to 11 T), along with indirect methods, we have found low and high field regularities of the magnetocaloric effect characterized by the adiabatic temperature change, DTad, and the isothermal magnetic entropy change, DSmag. The magnetocaloric properties near the phase transition are discussed in the framework of the Landau theory for the second-order phase transitions. (C) 2017 Elsevier B.V. All rights reserved.