Enhancement of magnetocaloric efficiency of $\mathrm{Gd}$ spacer between strong ferromagnets

The magnetocaloric properties of a thin spacer of gadolinium $(\mathrm{Gd})$ between layers of “strong” ferromagnets (relatively high Curie temperatures) are studied experimentally. It is found that, at room temperatures, the magnetocaloric efficiency $\Delta S/\Delta H$ ($\Delta S$ is the isothermal magnetic entropy change and $\Delta H$ is the range of applied magnetic fields) of $\mathrm{Gd}$ spacer of thickness of $3$ nm is up to two orders in magnitude higher than this value in an individual thicker ($30$ nm) $\mathrm{Gd}$ layer. This opens up opportunities for using the magnetocaloric effect in micro(nano)electronics and biomedicine using relatively weak magnetic fields $H<1$ kOe. The observed increase in the magnetocaloric efficiency is explained by the influence of direct exchange coupling between $\mathrm{Gd}$ spacer and its surroundings, which changes the distribution of magnetization in the spacer and, ultimately, its magnetocaloric potential.