Role of lanthanum in modifying the magnetic state in RNi2 solid solutions with R = Tb, Dy, Ho

Comparative analysis and generalization of the influence of La on the structural and magnetic properties of R1-xLaxNi2 (R = Tb, Dy, Ho) solid solutions is presented. All the studied R1-xLaxNi2 solid solutions solidify with the formation of a Laves-phase superstructure corresponding to the F (4) over bar 3m space group. The magnetic properties are dominated by rare earth interactions and the substitution of R atoms with La significantly modifies the magnetic behaviour of the R1-xLaxNi2 system. Replacing of magnetic R with the nonmagnetic La results in magnetic dilution leading to the weakening of exchange interactions and decrease of the ordering temperature. In the case of Tb1-xLaxNi2 and Dy1-xLaxNi2 the ferromagnetic properties are reduced as the lanthanum content increases to 80% and for Ho1-xLaxNi2 the ferromagnetic ordering is destroyed as the lanthanum content increases to the values above 80%. The magnetic transition in all the studied samples is of second order character. The Debye temperature, phonon and conduction electron contributions as well as a magnetic contribution to the heat capacity have been determined from heat capacity measurements. The magnetocaloric effect and the refrigerant cooling power for selected solid solutions was determined in magnetic fields up to 4.2 T. (C) 2015 Elsevier B.V. All rights reserved.