Strong magnetocaloric effect induced by spin reorientation transitions in epitaxial Ho thin films

Magnetocaloric effect (MCE) in an antiferromagnetic holmium (Ho) film is studied near the spin reorientation temperatures. A series of magnetization isotherms from 60 to 150 K around the N\'eel temperature, ${T}_N\ensuremath{\approx}130\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ were recorded for both in-plane and out-of-plane magnetic field orientations. A change in entropy, $\mathrm{\ensuremath{\Delta}}{S}_M$ of $\text{--}5\phantom{\rule{0.28em}{0ex}}\mathrm{J}/\mathrm{kg}\mathrm{K}$ was found near ${T}_N$ for an in-plane field orientation. A large change in $\mathrm{\ensuremath{\Delta}}{S}_M$ of \ensuremath{-}11.8 J/kg K due to a fan-helix spin transition at $T=90\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is observed for an in-plane field orientation. Spin transition at both ${T}_N$ and at the fan-helix transition exhibit larger MCE in the in-plane field orientations in comparison with the perpendicular orientation. The value of the refrigerant capacity extracted from the temperature dependence of $\mathrm{\ensuremath{\Delta}}{S}_M(T)$ is found to be larger for the ``in- plane'' orientation by a factor of two.