Magneto-transport properties of NiCoCrFePd high entropy alloy films

Abstract

This study aims to develop for the first time thin films of NiCoCrFePd high entropy alloy (HEA) to investigate the structural, magnetic, and transport properties for potential room temperature spin gapless semiconducting (SGS) applications. The as grown films were subjected to different annealing temperatures ranging from 400 °C to 600 °C to investigate the role of thermal generation of charge carriers and its effect on the (SGS) properties. The temperature dependent X-ray diffraction unveils structural stability down to 30 K with no phase transformations, however improvement in the crystallinity was observed with the increase in the annealing temperature. Rutherford backscattering spectroscopy shows depth dependent uniformity in the elemental distribution. Additionally, the magneto-transport studies revealed ferromagnetic behavior with a magnetic saturation values ranging from 165 emu/cm³ to 375 emu/cm³ and the Curie temperatures in the range of 263 K to 507 K. Further, the resistivity measurements confirmed a semiconducting behavior, with negative magnetoresistance corresponding to all the annealed samples. A two-channel conduction mechanism is used to explain the transport behaviour with one gapless and another gapped channel with activation energies ranging from 216.47 ± 3.63 meV to 86.85 ± 0.93 meV for different annealed samples. The observation of small anomalous Hall conductivity ranging from 25.2 Scm⁻¹ to 66.7 Scm⁻¹ and vanishing thermoelectric power lying in the range 3.11 μV/K to 4.11 μV/K confirms the SGS behavior with hole-dominant charge carriers. Thus, evidently the annealing temperature can be used to tune the spin transport properties by altering energy band gaps and density of states near the Fermi energy (${\epsilon }_F$).