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

Magnetic phase transition, magnetocaloric effect and critical parameters of Ni50-xCoxMn50-yAly (x = 5 and 10; y = 17, 18 and 19) rapidly quenched ribbons have been studied. X-ray diffraction patterns exhibit a coexistence of the L2(1) and 10M 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 Ni45Co5Mn31Al19 and Ni40Co10Mn33Al17 ribbons reveal both the positive and negative magnetocaloric effects. Under magnetic field change (Delta H) of 13.5 kOe, the maximum magnetic entropy change (vertical bar Delta S-m vertical bar(max) ) of the Ni45Co5Mn31Al19 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 Ni45Co5Mn31Al19 ribbon were determined to be T-C approximate to 290 K, beta approximate to 0.58, gamma approximate to 0.92 and delta approximate to 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.