In Gd microwires obtained by ultrafast cooling of the melt, a change in the magnetic entropy of 12 J/kg K was determined at a Curie temperature of 293 K in a magnetic field of 5 T. This value coincides with the change in the magnetic part of the entropy in bulk single-crystal samples in the same field. It has been found that in a strong magnetic field of 9 T, the temperature dependence of the entropy exhibits two maxima at temperatures of 292 and 312 K. The appearance of an additional entropy maximum in microstructured samples is caused by high mechanical microstresses retained in the sample after ultrafast cooling.
In W/Gd/W/MgO heterostructures, the dependence of mechanical stresses in the Gd film on the crystallographic orientation of the MgO substrate was revealed. Variations in the interplanar spacings in MgO in different orientations create tensile elastic stresses up to 0.22 GPa in the Gd film, which are transferred through the damping layer W. It is found that these stresses affect the isothermal magnetization curves, the corresponding change in the magnetic part of the entropy at the Curie point Tc = 293 K, and the relative cooling capacity (RCP). This allows us to consider mechanical stresses as a factor in controlling the magnetocaloric cycle, which increases the efficiency of the refrigeration machine, when mechanical loading is synchronized with the heating-cooling cycles of the ferromagnet.
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