Magnetic and magnetocaloric properties of itinerant-electron system Hf_1−xTa_xFe₂ (x = 0.125 and 0.175)

Highlights: • First report of the direct measurement of ΔT_ad in Hf_1−xTa_xFe₂ compounds. • ΔT_ad reach values of 2.5 K under μ₀ΔH = 3 T for x = 0.175 compound. • A field induced metamagnetic phase transition has been observed. - Abstract: Intrinsic magnetic properties and magnetocaloric effect (MCE) have been investigated for Hf_1−xTa_xFe₂ (x = 0.125 and 0.175) itinerant-electron compounds which exhibit a temperature-induced transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) state. Upon increasing Ta concentration, the ferromagnetic ordering temperature strongly decreases with decreasing the lattice parameters and both the isothermal magnetic entropy change ΔS_M and the adiabatic temperature change ΔT_ad are enhanced. An adiabatic temperature change of ΔT_ad = 2 and 2.5 K was observed in Hf_0.875Ta_0.125Fe₂ and Hf_0.825Ta_0.175Fe₂, respectively, for a magnetic field change of 3 T. Therefore, the partial substitution of Ta for Hf is highly effective in the enhancement of the magnetocaloric effect in Hf_1−xTa_xFe₂ systems. In addition substitution can be used to tune both the transition temperature but also the magnetic transition from first toward second order type