Magnetocaloric effect in Tb₃₁Co₆₉ and Dy₃₁Co₆₉ thin films deposited on Si substrates

We present the structural, magnetic, and magnetocaloric properties of thin films with stoichiometry Tb₃₁Co₆₉ and Dy₃₁Co₆₉ deposited on naturally oxidized silicon Si (100) substrates. Samples with a thickness $d=50$ nm covered with a protective Au overlayer with a thickness dAu =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 Tcomp of the amorphous phase for Tb₃₁Co₆₉ at 81.5 K and for Dy₃₁Co₆₉ at 88.5 K, while we found the Curie temperature TC,\ 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 Tcomp of amorphous phases and TC,\ Laves of crystallized Laves phases. The analysis for the magnetic field change of Δμ₀H=5 T showed values of the magnetic entropy change of -ΔSM=4.9 mJ cm⁻³ K⁻¹ at Tcomp and -ΔSM=6.6 mJ cm⁻³ K⁻¹ at TC,\ Laves for Tb₃₁Co₆₉, while for Dy₃₁Co₆₉, we determined the values of -ΔSM=35 mJ cm⁻³ K⁻¹ at Tcomp and -ΔSM=28 mJ cm⁻³ K⁻¹ at TC,\ Laves.