Influence of a Cyclic Magnetic Field on the Direct and Inverse Magnetocaloric Effects in the Ni₄₄Co₆Mn₃₂Al₁₈ Heusler Ribbon

The results of direct measurements for the adiabatic temperature change ∆T_ad in a rapidly quenched ribbons Heusler Ni₄₄Co₆Mn₃₂Al₁₈ alloy specimen within a temperature range of 100–350 K in a cyclic magnetic field with a strength of 18 kOe and a frequency of 0.2 Hz are presented. It is shown that, in the case of one-time magnetic field actuation, the inverse effect value is –0.25 K at a magnetostructural transition temperature T_S. The second and following on/off cycles lead to a decrease in the effect by an order of magnitude to –0.03 K. Such a behavior is associated with the effect of kinetic relaxation in the martensite phase and phase transition irreversibility in the used magnetic fields. Near T_C, the stable and direct effect ∆T_ad = 0.23 K without degradation signs is observed.