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 $d_{\mathrm{Au}}=5$ 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 $T_{\mathrm{comp}}$ 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 $T_{\mathrm{C},\mathrm{Laves}}$ 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 $T_{\mathrm{comp}}$ of amorphous phases and $T_{\mathrm{C},\mathrm{Laves}}$ of crystallized Laves phases. The analysis for the magnetic field change of $\Delta {\mu }_{0}H=5$ T showed values of the magnetic entropy change of $-\Delta S_{\mathrm{M}}=4.9$ mJ cm${}^{-3}$ K${}^{-1}$ at $T_{\mathrm{comp}}$ and $-\Delta S_{\mathrm{M}}=6.6$ mJ cm${}^{-3}$ K${}^{-1}$ at $T_{\mathrm{C},\mathrm{Laves}}$ for Tb${}_{31}$Co${}_{69}$, while for Dy${}_{31}$Co${}_{69}$, we determined the values of $-\Delta S_{\mathrm{M}}=35$ mJ cm${}^{-3}$ K${}^{-1}$ at $T_{\mathrm{comp}}$ and $-\Delta S_{\mathrm{M}}=28$ mJ cm${}^{-3}$ K${}^{-1}$ at $T_{\mathrm{C},\mathrm{Laves}}$.