High-Sensitivity Tunnel Magnetoresistance Sensors Based on Double Indirect and Direct Exchange Coupling Effect

Detection of ultralow magnetic field requires magnetic sensors with high sensitivity and low noise level,especially for low operating frequency applications.We investigated the transport properties of tunnel magnetoresistance(TMR)sensors based on the double indirect exchange coupling effect.The TMR ratio of about 150%was obtained in the magnetic tunnel junctions and linear response to an in-plane magnetic field was successfully achieved.A high sensitivity of 1.85%/Oe was achieved due to a designed soft pinned sensing layer of CoFeB/NiFe/Ru/IrMn.Furthermore,the voltage output sensitivity and the noise level of 10.7 mV/V/Oe,10 nT/Hz^(1/2)at 1 Hz and3.3 nT/Hz^(1/2)at 10 Hz were achieved in Full Wheatstone Bridge configuration.This kind of magnetic sensors can be used in the field of smart grid for current detection and sensing.

Nonlinear three-magnon scattering in low-damping La_(0.67)Sr_(0.33)MnO_(3)thin films

Three-magnon scattering,a nonlinear process in which a high-energy magnon splits into two low-energy magnons with energy and momentum conservation,has been widely studied in the magnonics community.Here,we report experimental observation of nonlinear three-magnon scattering in La_(0.67)Sr_(0.33)MnO_(3)thin films with low magnetic damping(~10^(-4))by all-electric and angle-resolved spin wave spectroscopy.The reflection spectra of the spin wave resonance with high-power excitation at Damon–Eshbach configuration demonstrate a scattering regime with gradual signal disappearance,where a magnon of Damon–Eshbach mode decays into two magnons of volume mode above the threshold power(-10 dBm)of the injected microwave.The nonlinear scattering is only allowed at low-field regime and the calculated dispersions of dipole-exchange spin wave claim the mechanism of allowed and forbidden three-magnon scattering.The films and heterostructures of La_(0.67)Sr_(0.33)MnO_(3)have been already demonstrated with rich physical phenomena and great versatility,in this work the nonlinear magnetic dynamics of La_(0.67)Sr_(0.33)MnO_(3)thin films is revealed,which offer more possibility for applications to oxide magnonics and nonlinear magnonic devices.

Giant Tunneling Magnetoresistance in Spin-Filter Magnetic Tunnel Junctions Based on van der Waals A-Type Antiferromagnet CrSBr

Two-dimensional van der Waals magnetic materials have demonstrated great potential for new-generation high-performance and versatile spintronic devices.Among them,magnetic tunnel junctions(MTJs)based on A-type antiferromagnets,such as CrI_(3),possess record-high tunneling magnetoresistance(TMR)because of the spin filter effect of each insulating unit ferromagnetic layer.However,the relatively low working temperature and the instability of the chromium halides hinder applications of this system.Using a different technical scheme,we fabricated the MTJs based on an air-stable A-type antiferromagnet,CrSBr,and observed a giant TMR of up to 47000%at 5 K.Meanwhile,because of a relatively high Néel temperature of CrSBr,a sizable TMR of about 50%was observed at 130 K,which makes a big step towards spintronic devices at room temperature.Our results reveal the potential of realizing magnetic information storage in CrSBr-based spin-filter MTJs.

Nonreciprocal coherent coupling of nanomagnets by exchange spin waves

Nanomagnets are widely used to store information in non-volatile spintronic devices.Spin waves can transfer information with low-power consumption as their propagations are independent of charge transport.However,to dynamically couple two distant nanomagnets via spin waves remains a major challenge for magnonics.Here we experimentally demonstrate coherent coupling of two distant Co nanowires by fast propagating spin waves in an yttrium iron garnet thin film with sub-50 nm wavelengths.Magnons in two nanomagnets are unidirectionally phase-locked with phase shifts controlled by magnon spin torque and spin-wave propagation.The coupled system is finally formulated by an analytical theory in terms of an effective non-Hermitian Hamiltonian.Our results are attractive for analog neuromorphic computing that requires unidirectional information transmission.

Room temperature ferromagnetism in ultra-thin van der Waals crystals of 1T-CrTe2

Although many emerging new phenomena have been unraveled in two dimensional(2D)materials with long-range spin orderings,the usually low critical temperature in van der Waals(vdW)magnetic material has thus far hindered the related practical applications.Here,we show that ferromagnetism can hold above 300 K in a metallic phase of 1T-CrTe2 down to the ultra-thin limit.It thus makes CrTe2 so far the only known exfoliated ultra-thin vdW magnets with intrinsic long-range magnetic ordering above room temperature.An in-plane room-temperature negative anisotropic magnetoresistance(AMR)was obtained in ultra-thin CrTe2 devices,with a sign change in the AMR at lower temperature,with−0.6%and+5%at 300 and 10 K,respectively.Our findings provide insights into magnetism in ultra-thin CrTe2,expanding the vdW crystals toolbox for future room-temperature spintronic applications.

Field-free approaches for deterministic spin–orbit torque switching of the perpendicular magnet

All-electrical driven magnetization switching attracts much attention in next-generation spintronic memory and logic devices,particularly in magnetic random-access memory(MRAM)based on the spin–orbit torque(SOT),i.e.SOT-MRAM,due to its advantages of low power consumption,fast write/read speed,and improved endurance,etc.For conventional SOT-driven switching of the magnet with perpendicular magnetic anisotropy,an external assisted magnetic field is necessary to break the inversion symmetry of the magnet,which not only induces the additional power consumption but also makes the circuit more complicated.Over the last decade,significant effort has been devoted to field-free magnetization manipulation by using SOT.In this review,we introduce the basic concepts of SOT.After that,we mainly focus on several approaches to realize the field-free deterministic SOT switching of the perpendicular magnet.The mechanisms mainly include mirror symmetry breaking,chiral symmetry breaking,exchange bias,and interlayer exchange coupling.Furthermore,we show the recent progress in the study of SOT with unconventional origin and symmetry.The final section is devoted to the industrial-level approach for potential applications of field-free SOT switching in SOT-MRAM technology.