arXiv subjects

Fanxing Zheng

Publications and source records attributed to Fanxing Zheng.

9 recordsLinked to original sources

arXiv2025

Inefficiency of orbital Hall effect on the spin torque in transition metal/ferromagnet bilayers

Current induced spin torque is essential and crucial in spintronics. In this work, we systematically investigate the spin torque in transition metal(TM)/ferromagnet(FM) bilayers by using first-principles calculations and taking into account the phonon scattering at room temperature. To examine the spin and orbital Hall contribution, the studied transition metals include 5d heavy metals Pt, W, Au as well as 3d light metals Ti, V, Cr, Cu etc. We found that in TM/CoFe bilayers with typical 3d and 5d transition metals, the spin torque on CoFe mainly originates from spin Hall mechanism with the magnitude and sign of damping like torque efficiency consistent with the spin Hall conductivity. In TM/Ni bilayers, the spin torque is contributed by three mechanisms including spin and orbital Hall current in TM, as well as self-torque in Ni. The orbital Hall contribution in TM is accompanied by noteworthy opposite self spin torque in Ni, which leads to inapparent torque efficiency in Ti/Ni and V/Ni bilayers. For TM(5d heavy metal)/Ni bilayers, the spin torque induced by orbital Hall and self-torque in Ni nearly cancel each other, which makes the spin torque on Ni still align with that of the spin Hall effect in TM. Our work reveals much less efficient contribution of orbital Hall than spin Hall effect on the spin torque in transition metal/ferromagnet bilayers.

cond-mat.mtrl-sci↗

arXiv2025

Nonrelativistic spin-splitting multiferroic antiferromagnet and compensated ferrimagnet with zero net magnetization

Spin-splitting antiferromagnets with spin-polarized band structures in momentum space have garnered intensive research attention due to their zero net magnetic moments, ultras fast spin dynamics as conventional antiferromagnets, and spin-polarized transport properties akin to ferromagnets, making them promising candidates for antiferromagnetic spintronics. However, unlike spin-torque switching of ferromagnets by electric current, efficient electric control of spin-splitting antiferromagnetic order remains challenges. In this work, we identify prototypes of multiferroic spin-splitting antiferromagnets, including BiFeO3, Fe2Mo3O8 and compensated ferrimagnet GaFeO3 with ferroelectric polarization as well as spin-polarized electronic structures. We establish design principles for the spin-splitting multiferroic antiferromagnets and compensated ferrimagnets, elucidating the band symmetry features in Brillouin zone. We demonstrate that the spin polarization in spin-splitting magnets, despite of zero net magnetic moment, can be switched by ferroelectric polarization, providing an efficient means of controlling the antiferromagnetic order. Our work may inspire future development of novel multiferroic functional magnets with zero magnetic moments and pave the way for their applications in magnetoelectric spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Spin Hall effect in 3d ferromagnetic metals for field-free switching of perpendicular magnetization: A first-principles investigation

Ferromagnetic metals, with the potential to generate spin current with unconventional spin polarization via the spin Hall effect, offer promising opportunities for field-free switching of perpendicular magnetization and for the spin-orbit torque devices. In this study, we investigate two distinct spin Hall mechanisms in 3d ferromagnetic metals including spin-orbit coupling driven spin Hall effect in Fe, Co, Ni and their alloys, and non-relativistic spin Hall effect arising from anisotropic spin-polarized transport by taking L10-MnAl as an example. By employing first-principles calculations, we examine the temperature and alloy composition dependence of spin Hall conductivity in Fe, Co, Ni and their alloys. Our results reveal that the spin Hall conductivities with out-of-plane spin polarization in 3d ferromagnetic metals are at the order of 1000 \frac{\hbar}{2e} \left( Ω\, \text{cm} \right)^{-1} at 300 K, but with a relatively low spin Hall angles around 0.01~0.02 due to the large longitudinal conductivity. For L10-MnAl(101), the non-relativistic spin Hall conductivity can reach up to 10000\frac{\hbar}{2e} \left( Ω\, \text{cm} \right)^{-1}, with a giant spin Hall angle around 0.25 at room temperature. By analyzing the magnetization switching process, we demonstrate deterministic switching of perpendicular magnetization without an external magnetic field by using 3d ferromagnetic metals as spin current sources. Our work may provide an unambiguous understanding on spin Hall effect in ferromagnetic metals and pave the way for their potential applications in related spintronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Crystal facet orientation and temperature dependence of charge and spin Hall effects in noncollinear antiferromagnet: A first-principles investigation

Noncollinear antiferromagnets (nc-AFMs) have attracted increasing research attention in spintronics due to their unique spin structures and fascinating charge and spin transport properties. By using first-principles calculations, we comprehensively investigate the charge and spin Hall effects in representative noncollinear antiferromagnet Mn3Pt. Our study reveals that the Hall effects in nc-AFMs are critically dependent on the crystal facet orientation and temperature. For (001) orientated Mn3Pt, each charge and spin Hall conductivity element is comprised of both time reversal odd (T-odd) and even (T-even) contribution, associated with longitudinal conductivity, which leads to sizable and highly anisotropic Hall conductivity. The temperature dependence of charge and spin Hall conductivity has been elucidated by considering both phonon and spin disorder scattering. The scaling relations between Hall conductivity and longitudinal conductivity have also been investigated. The existence of prominent spin Hall effect in nc-AFMs may generate spin current with Sz spin polarization, which is advantageous for field free switching of perpendicular magnetization. Our work may provide unambiguous understanding on the charge and spin transport in noncollinear antiferromagnets and pave their way for applications in antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2023

Anatomy of spin Hall effect in ferromagnetic metals

The spin Hall effect in nonmagnetic materials has been intensively studied and became one of the most crucial spin-charge conversion mechanism in spintronics. However, the spin Hall effect in ferromagnetic metals has been less investigated and remains unclear. In this work, we investigate the spin Hall effect in representative ferromagnetic alloy by using first-principles calculations. We first clarify the spin Hall effect into three different types including conventional (CSHE), spin anomalous (SAHE) and magnetic spin Hall effect (MSHE) and then calculate the corresponding spin Hall conductivity and spin Hall angle for (Fe, Co, Ni)Pt, NiFe and CoFe alloy. We find the above three spin Hall mechanisms do coexist in ferromagnetic metals. Particularly, for Pt-based ferromagnetic alloy, a sizable conventional and magnetic spin Hall angles comparable to that of Pt have been predicted. The remarkable unconventional spin Hall effect in ferromagnetic metal may enrich the spin-charge conversion phenomena. For instance, the spin current generated by remarkable MSHE with out-of-plane spin-polarization should be helpful for field-free switching of perpendicular magnetization through spin-orbit torque effect. This work may stimulate future studies on the spin Hall effect in ferromagnetic metals and pave their promising applications for spin-charge conversion devices in spintronics.

cond-mat.mtrl-sci↗

arXiv2022

Tremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe$_3$GaTe$_2$ with highly spin-polarized Fermi surfaces

Recently, van der Waals (vdW) magnetic heterostructures have received increasing research attention in spintronics. However, the lack of room-temperature magnetic order of vdW material has largely impedes its development in practical spintronics devices. Inspired by the recently discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic order above room temperature and sizable perpendicular magnetic anisotropy, we investigate the basic electronic structure and magnetic properties of Fe3GaTe2 as well as tunneling magnetoresistance effect in magnetic tunnel junctions (MTJs) with structure of Fe3GaTe2/Insulator/Fe3GaTe2 by using first-principles calculations. It is found that Fe3GaTe2 with highly spin-polarized Fermi surface ensures that such magnetic tunnel junctions may have prominent tunneling magnetoresistance effect at room temperature even comparable to existing conventional AlOx and MgO-based MTJs. Our results suggest that Fe3GaTe2-based MTJs may be the promising candidate for realizing long-waiting full magnetic vdW spintronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Tunneling Magnetoresistance in Noncollinear Antiferromagnetic Tunnel Junctions

Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics driven by the advantages of antiferromagnets producing no stray fields and exhibiting ultrafast magnetization dynamics. The efficient method to detect an AFM order parameter, known as the Néel vector, by electric means is critical to realize concepts of AFM spintronics. Here, we demonstrate that non-collinear AFM metals, such as Mn3Sn, exhibit a momentum dependent spin polarization which can be exploited in AFM tunnel junctions to detect the Néel vector. Using first-principles calculations based on density functional theory, we predict a tunneling magnetoresistance (TMR) effect as high as 300% in AFM tunnel junctions with Mn3Sn electrodes, where the junction resistance depends on the relative orientation of their Néel vectors and exhibits four non-volatile resistance states. We argue that the spin-split band structure and the related TMR effect can also be realized in other non-collinear AFM metals like Mn3Ge, Mn3Ga, Mn3Pt, and Mn3GaN. Our work provides a robust method for detecting the Néel vector in non-collinear antiferromagnets via the TMR effect, which may be useful for their application in AFM spintronic devices.

cond-mat.mtrl-sci↗

arXiv2021

Current-Perpendicular-to-Plane Giant Magnetoresistance Effect in van der Waals Heterostructures

Spin-dependent transport in a full van der Waals (vdW) giant magnetoresistance (GMR) junctions with the structure of Fe3GeTe2/XTe2/Fe3GeTe2 (X = Pt, Pd) has been investigated by using first-principles calculations. The ballistic conductance, magnetoresistance (MR) and resistance-area product (RA) have been calculated in a current-perpendicular-to-plane (CPP) geometry. A giant magnetoresistance of around 2000% and RA less than 0.3 Ω μm2 have been found in the proposed vdW CPP GMR. In addition, the spin-orbit coupling effect on transport and anisotropy magnetoresistance (AMR) has also been investigated. The calculated AMR is found to be around 20% in Fe3GeTe2/trilayer-PdTe2/Fe3GeTe2 CPP GMR. Both GMR and AMR in the proposed vdW CPP GMR mainly originate from the bulk electronic structure properties of Fe3GeTe2. This work demonstrates a vdW CPP GMR with superior advantages including perpendicular magnetic anisotropy, large GMR, low RA as well as sizable AMR may stimulate future experimental explorations and should be appealing for their applications in spintronic devices including magnetic sensor and memory.

cond-mat.mtrl-sci↗

arXiv2021

Ferroelectric control of Néel vector in L10 type of antiferromagnetic films

How to efficiently manipulate the Néel vector of antiferromagnets (AFM) by electric methods is one of the major focuses in current antiferromagnetic spintronics. In this work, we investigated the ferroelectric control of magnetism in AFM L10-MnPt/BaTiO3 bilayers structures by using first-principles calculation. We studied the effect of ferroelectric polarization reversal on magnetic crystalline anisotropy (MCA) of L10-MnPt films with different interface structures. Our results predict a large perpendicular MCA in L10-MnPt films with Pt-O interface, while an in-plane MCA with Mn-O interface when they are interfaced with ferroelectric BaTiO3. In addition, the magnitude of MCA for both interfaces can be modulated efficiently by the polarization reversal of BaTiO3. The ferroelectric control of MCA has been analyzed based on second order perturbation theory, and it can be mainly attributed to the ferroelectric polarization driven redistribution of Pt-5d orbital occupation around Fermi energy. Especially, for Mn-O interface, the Néel vector can be switched between in-plane [100] and [110] directions, or even from in-plane to out-of-plane at certain film thickness by reversing ferroelectric polarization. Our results may provide a non-volatile concept for ferroelectric control of Néel vector in L10-antiferromagnets, which could stimulate experimental investigations on magnetoelectric effect of antiferromagnets and promote its applications in low-power consumption spintronic memory devices.

cond-mat.mtrl-sci↗