Spin-Hall effect and emergent antiferromagnetic phase transition in n-Si

TL;DR

This paper reports the observation of the spin-Hall effect and an emergent antiferromagnetic phase transition in n-type silicon, linked to spin accumulation and Rashba effect, with implications for thermal transport and phase behavior.

Contribution

It demonstrates the occurrence of spin-Hall effect and a novel antiferromagnetic phase transition in silicon, highlighting the role of spin diffusion length and Rashba effect without requiring a two-dimensional electron gas.

Findings

Spin-Hall effect observed in n-Si with thermal and magnetoresistance signatures.

Emergent antiferromagnetic phase transition at 270 K detected via 3omega method.

Spin accumulation influences thermal transport behavior in silicon.

Abstract

Spin current experiences minimal dephasing and scattering in Si due to small spin-orbit coupling and spin-lattice interactions is the primary source of spin relaxation. We hypothesize that if the specimen dimension is of the same order as the spin diffusion length then spin polarization will lead to non-equilibrium spin accumulation and emergent phase transition. In n-Si, spin diffusion length has been reported up to 6 {\mu}m. The spin accumulation in Si will modify the thermal transport behavior of Si, which can be detected with thermal characterization. In this study, we report observation of spin-Hall effect and emergent antiferromagnetic phase transition behavior using magneto-electro-thermal transport characterization. The freestanding Pd (1 nm)/ Ni80Fe20 (75 nm)/ MgO (1 nm)/ n-Si (2 micron) thin film specimen exhibits a magnetic field dependent thermal transport and spin-Hall magnetoresistance behavior attributed to Rashba effect. An emergent phase transition is discovered using self-heating 3omega method, which shows a diverging behavior at 270 K as a function of temperature similar to a second order phase transition. We propose that spin-Hall effect leads to the spin accumulation and resulting emergent antiferromagnetic phase transition. We propose that the length scale for Rashba effect can be equal to the spin diffusion length and two-dimensional electron gas is not essential for it. The emergent antiferromagnetic phase transition is attributed to the site inversion asymmetry in diamond cubic Si lattice.