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Advanced materials: giant piezoelectric spin effect in noncollinear antiferromagnetic metals

wallpapers News 2020-07-03
After

have entered the information age the total amount of information in human society has grown explosively the amount of global information storage has increased sharply which puts forward higher requirements for the speed energy consumption stability density of information storage. At present magnetic memory devices are mainly based on ferromagnetic materials. Compared with ferromagnetic materials antiferromagnetism has obvious advantages: insensitive to external magnetic field fast response speed high integration density. Therefore antiferromagnetic spin devices are expected to be used in magnetic rom access memory artificial neural network THz logic memory devices THz source tables detectors. Based on the advantages great potential of antiferromagnetic materials antiferromagnetic spintronics has gradually become a research hotspot. At present antiferromagnetic spintronics devices mainly use the anisotropic magnetoresistance effect in antiferromagnetism but its variation is only about 0.1% which is not realistic for practical applications. In order to overcome this difficulty it is urgent to improve the output signal of spin devices.

Professor Liu Zhiqi of Beijing University of Aeronautics Astronautics proposed that abnormal Hall resistance antiferromagnetic tunnel junction can provide enough spin signal output. In addition because the antiferromagnetic spin is not sensitive to the magnetic field researchers turn to use the electric field to produce piezoelectric stress in the ferroelectric material acting on the noncollinear antiferromagnetic material mn3ga which is extremely sensitive to the spin structure stress so as to realize the regulation of the antiferromagnetic material. Non collinear antiferromagnetic mn3ga films were grown on 0.7pbmg1/3nb2/3o3-0.3pbtio3 (PMN-PT) by magnetron sputtering. By applying electric field to the ferroelectric substrate compressive stress will be generated in the substrate then act on the antiferromagnetic film. Due to the existence of intrinsic non-zero Bailey curvature non collinear antiferromagnetism can exhibit anomalous Hall effect. As a pseudo magnetic field in momentum space Bailey curvature originates from the interaction between Bloch electron bs. Therefore the change of anomalous Hall effect indicates the change of spin structure in noncollinear antiferromagnetic materials. An electric field of 4 kV cm-1 can modulate the anomalous Hall resistance of mn3ga by more than one order of magnitude which indicates that the spin structure of noncollinear antiferromagnetic mn3ga has changed greatly is very sensitive to piezoelectric stress. At the same time the researchers found that the samples excited by the electric field have very weak magnetism at room temperature the exchange coupling effect with the ferromagnetic material co90fe10 is also enhanced. These phenomena also indicate that the spin structure of mn3ga does change after the piezoelectric stress. Then the theoretical calculation shows that the density of states of Fermi level in non collinear mn3ga is very sensitive to the spin rotation angle. Due to the close relationship between the tunneling anisotropic magnetoresistance the density of states at the Fermi level of the material the researchers have fabricated nano scale antiferromagnetic mn3ga based tunneling junction devices by electron beam lithography. The experimental results show that the maximum resistance variation of the tunnel junction can reach 10.7% when the voltage of - 4 4 kV cm-1 is applied. At 0 kV cm-1 there is still about 9.8% nonvolatile resistance change. Using mn3ga we have successfully fabricated an antiferromagnetic tunnel junction device with high efficiency of electric field control. This work provides a new idea direction for the use of noncollinear antiferromagnetic materials for large signal readout the application of spin devices with fast response low energy consumption high density.


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