Unified Framework for Charge-Spin Interconversion in Spin-Orbit Materials

Abstract

Materials with spin-orbit coupling are of great current interest for various spintronics applications due to the efficient electrical generation and detection of electron spins. Over the past decade, a large number of materials have been studied including topological insulators, transition metals, Kondo insulators, semimetals, semiconductors, oxide interfaces, etc., however, there is no unifying physical framework for understanding the physics and therefore designing a material system and devices with the desired properties. We present a model that binds together the experimental data observed on the wide variety of materials in a unified manner. We show that, in a material with a given spin orbit coupling, the density of states plays a key role in determining the spin-charge interconversion efficiency and a simple inverse relationship can be obtained. Remarkably, experimental data on spin voltage, obtained over the last decade on many different material systems closely follow such inverse relationship. Based on such analytical relationship, we further deduce two figure of merits of great current interest: the spin-orbit torque efficiency (for the direct effect) and the inverse Rashba-Edelstein effect length (for the inverse effect), which statistically show good agreement with the existing experimental data on wide varieties of materials.

Spintronic Quantum Phase Transition in a Graphene/Pb0.24Sn0.76Te Heterostructure with Giant Rashba Spin‐Orbit Coupling

“…[ 21 ] In previous studies, spontaneous, non‐equilibrium spin polarization due to either the Rashba effect or topological surface state spin‐momentum locking is distinguishable by having opposite signs in the vector p Rashba . However, as many others have noted, [ 34,45,49 ] it is difficult to draw any conclusions about the sign of the polarization. Therefore, an absolute value of polarization was calculated, displayed versus temperature in Figure 4.…”

“…where h is Planck's constant, e is the elementary charge, P FM is the polarization of the ferromagnetic detector contact (∼48% for Ni 80 Fe 20 ), [49] v F is the Fermi velocity, m * is the effective mass, W is the width of the channel, p Rashba is the induced spin polarization due to the Rashba effect, and m u is a unit vector along the direction of magnetization. [21] In previous studies, spontaneous, nonequilibrium spin polarization due to either the Rashba effect or topological surface state spin-momentum locking is distinguishable by having opposite signs in the vector p Rashba .…”

The high magnetoresistance performance of epitaxial half-metallic CrO2-based magnetic junctions

“…The discovery of the giant magnetoresistance (GMR) effect has had a profound impact in the field of data reading technology, and relevant spintronic devices based on magnetic junctions (MJs), such as magnetic random access memory (MRAM), spintransfer torque (STT) MRAM, and spin-orbit torque (SOT) MRAM, are promising candidates for high-density and ultrafast storage technology. [1][2][3][4][5][6][7] According to Julliere's theory, the performance of magnetic tunnel junction (MTJ) devices is strongly associated with the spin polarizations of the bottom and top electrodes, i.e., TMR ratio = 2P 1 P 2 /(1 À P 1 P 2 ), where P 1 and P 2 are the spin polarizations of the two ferromagnetic electrodes at the Fermi level, respectively. 8 Therefore, in order to manufacture MTJ devices with efficient performance, an appropriate selection of ferromagnetic electrodes with high spin polarizations is of crucial importance.…”