Magnetic properties of the off-stoichiometric GdNi2Mnx alloys

• The off-stoichiometric GdNi2Mnx compounds with the MgCu2 structure exist up to х = 0.35.
• Starting from the composition х ⩾ 0.4, in the samples there forms the PuNi3-type phase.
• Increase in the Mn content leads to a considerable growth of the Curie temperature.
• The Ni moment increases up to maximal value already for smallest Mn content.
• The maximum isothermal entropy change is 4.6 J kg−1 K−1 for the GdNi2Mn0.4 alloy.

The structure and magnetic properties of the off-stoichiometric GdNi2Mnx (0 ⩽ x ⩽ 0.6) alloys have been studied. The alloys with 0 < х < 0.4 crystallize in a cubic structure of the MgCu2-type, whereas, starting from the composition х ⩾ 0.4, in the samples there forms the PuNi3-type phase. Increase in the Mn content is found to lead to a considerable growth of the Curie temperature from 80 K for the binary GdNi2 up to 190 K for the GdNi2Mn0.4 alloy. Magnetization at 4 K decreases with increasing x, which indicates the formation of a ferrimagnetic structure. The magnetic entropy change has been determined from the temperature dependences of the magnetization using the Maxwell equation. For GdNi2Mn0.4, upon changing the magnetic field from 0 to 9 T, the isothermal entropy change in the vicinity of the Curie temperature has been found to be 4.6 J kg−1 K−1. The results are discussed under assumption of growth of both the Ni magnetic moment and Gd–Mn and Ni–Mn exchange interactions with increasing the manganese content.