Influence of the Terbium film size for the magnetocaloric effect at low temperatures

TL;DR

This study demonstrates that ultrathin Terbium films exhibit significantly enhanced magnetocaloric effects near the Neel temperature, with potential for improved low-temperature cooling devices due to size and surface effects.

Contribution

It reveals that reducing Terbium film thickness markedly increases the magnetocaloric effect, especially near the Neel temperature, highlighting the importance of finite size effects in magnetic cooling applications.

Findings

Ultrathin Tb films show a tenfold increase in adiabatic temperature change near T_N.

Thin films with 6 monolayers have higher thermal caloric efficiency than thicker ones.

Magnetocaloric effect is significantly enhanced at low magnetic fields in ultrathin films.

Abstract

Significative enhance in magnetocaloric effect due to finite size and surface effects is reported in Terbium(Tb) thin films in the helimagnetic phase (corresponding to a temperature range from $T_C$=219 K to $T_N$=231 K), for external fields of the order of kOe. For a Tb thin film of 6 monolayers submitted to an applied field ($\Delta$H= 30 kOe, $\Delta$H= 50 kOe and $\Delta$H= 70 kOe) we report a significative change in adiabatic temperature, $\Delta$T/$\Delta$H, near the N\'eel temperature, of the order ten times higher than that observed for Tb bulk. On the other hand, for small values of the magnetic field, large thickness effects are found. For external field strength around few kOe, we have found that the thermal caloric efficiency increases remarkably for ultrathin films. For an ultrathin film with 6 monolayers, we have found $\Delta$T/$\Delta$H=43 K/T while for thicker films, with 20 monolayers, $\Delta$T/$\Delta$H=22 K/T. Our results suggest that thin films of Tb are a promising material for magnetocaloric effect devices for applications at intermediate temperatures.