Investigation of magnetic phase transition and magnetocaloric effect of (Ni,Co)-Mn-Al melt-spun ribbons

Abstract

Magnetic phase transition, magnetocaloric effect and critical parameters of Ni 50- x Co x Mn 50- y Al y ( x = 5 and 10; y = 17, 18 and 19) rapidly quenched ribbons have been studied. X-ray diffraction patterns exhibit a coexistence of the L 2 1 and 10 M crystalline phases of the ribbons. Magnetization measurements show that all the samples behave as soft magnetic materials with a low coercive force less than 60 Oe. The shape of thermomagnetization curves considerably depends on Co and Al concentrations. The Curie temperature ( T C ) of the alloy ribbons strongly increases with increasing the Co concentration and slightly decreases with increasing the Al concentration. The Ni 45 Co 5 Mn 31 Al 19 and Ni 40 Co 10 Mn 33 Al 17 ribbons reveal both the positive and negative magnetocaloric effects. Under magnetic field change ( Δ GH) of 13.5 kOe, the maximum magnetic entropy change (|Δ S m | max ) of the Ni 45 Co 5 Mn 31 Al 19 ribbon is about 2 and -1 J·kg −1 ·K −1 for negative and positive magnetocaloric effects, respectively. Basing on Arrott - Noakes and Kouvel - Fisher methods, critical parameters of the Ni 45 Co 5 Mn 31 Al 19 ribbon were determined to be T C ≈ 290 K, β ≈ 0.58, γ ≈ 0.92 and δ ≈ 2.59. The obtained values of the critical exponents indicate that the magnetic order of the alloy ribbon is close to the mean-field model.