Title : Structure, magnetic and transport properties of nano-crystalline thin films of NiCoCrFePd high entropy alloy
High entropy alloy (HEA) films having applications in various fields ranging from harsh environments to electronic devices. [1,2] Nanostructured high entropy thin films of Heuslers alloys found promising materials for room temperature spin gapless semiconductors [3-5]. E-beam evaporation technique is used to synthesized the thin film of NiCoCrFePd HEA at room temperatures and subsequently annealed at different temperatures. Further, the temperature dependent XRD revealed strongly (111) oriented face center cubic (FCC) structure of NiCoCrFePd thin films with no phase transformation and excellent stability down to 30 K temperature. Rutherford backscattering spectroscopy (RBS) along with energy dispersive X-ray (EDX) spectroscopy confirmed equiatomic composition with small deviation (?2 at.%) from the equiatomic target. Elemental mapping indicated the homogenous distribution of constituent elements with no phase segregations. M-T measurement conforms the ferromagnetic nature at room temperature in all the samples with the critical temperature (TC) decreases from 431 K to 375 K upon annealing. The temperature dependent resistivity measurement shows semiconducting behavior, which gets enhanced with increases in the annealing temperature. Measurement of nearly temperature independent carrier concentration (n) and vanishing thermopower indicates the spin gapless semiconducting behavior (SGS) in these films with hole as a dominating carrier. These class of recently discovered materials exhibits finite energy band gaps for one spin channel and block the other spin channel. The fermi energies of 3.94 eV, 2.14 eV, and 1.28 eV corresponding to A-400, A-500, and A-600 evaluated from the thermopower measurement shows an decrease in fermi energy with the annealing temperature.
Audience Take Away:
- Exotic transport properties with spintronics application of NiCoCrFePd thin films.
- Understanding the anomalous transport behavior of nanocrystalline HEA films.
- Opens new filed of paradigm for the applicability of HEA films in spintronics applications.