Magnetocaloric effect in Tb$_{31}$Co$_{69}$ and Dy$_{31}$Co$_{69}$ thin films deposited on Si substrates

Abstract

We present the structural, magnetic, and magnetocaloric properties of thin films with stoichiometry Tb$_{31}$Co$_{69}$ and Dy$_{31}$Co$_{69}$ deposited on naturally oxidized silicon Si (100) substrates. Samples with a thickness $d=50$ nm covered with a protective Au overlayer with a thickness $d_{\rm Au} =5 $ nm were produced using the pulsed laser deposition technique. X-ray diffraction analysis indicated the presence of crystallized Laves phases and amorphous phases in the prepared materials. Magnetization measurements as a function of temperature revealed ferrimagnetic behavior in both samples. We estimated the compensation temperature $T_{\rm comp}$ of the amorphous phase for Tb$_{31}$Co$_{69}$ at 81.5 K and for Dy$_{31}$Co$_{69}$ at 88.5 K, while we found the Curie temperature $T_{\rm C,\ Laves}$ of the crystallized Laves phases at 204.5 K and at 117 K, respectively. We investigated the magnetocaloric effect in a wide temperature range, covering $T_{\rm comp}$ of amorphous phases and $T_{\rm C,\ Laves}$ of crystallized Laves phases. The analysis for the magnetic field change of $\Delta \mu_0H=5$ T showed values of the magnetic entropy change of $-\Delta S_{\rm M}=4.9$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm comp}$ and $-\Delta S_{\rm M}=6.6$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm C,\ Laves}$ for Tb$_{31}$Co$_{69}$, while for Dy$_{31}$Co$_{69}$, we determined the values of $-\Delta S_{\rm M}=35$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm comp}$ and $-\Delta S_{\rm M}=28$ mJ cm$^{-3}$ K$^{-1}$ at $T_{\rm C,\ Laves}$.