Magneto-valve Effect Based On Magnetic Insulator

Facing the needs of information storage and logic operation in post-Moore era, spintronic devices provide promising development directions in the development of next-generation microelectronic devices with smaller cell size, non-volatile, low power consumption, and high speed. Among them, the spin valve is the core unit of various types of spintronic devices. The spin valve usually includes a sandwich core structure consisting of two layers of ferromagnetic metal and a non-magnetic intermediate layer, due to spin polarization electrons between the two ferromagnetic layers. Transport, so that the resistance of the device is modulated by the relative orientation of the two ferromagnetic layers. Spin-valve-based room-temperature giant magnetoresistance (GMR, 1988) and room-temperature tunneling magnetoresistance (TMR, 1995) devices have been widely used in high-density information storage and sensors such as magnetic hard disks, magnetic random access memories, and magnetic sensors. In the article, two scientists, A. Fert of France and P. Grünberg of Germany, won the 2007 Nobel Prize in physics for their discovery of the giant magnetoresistance (GMR) effect.

The spin wave is the collective excited state of the spin precession process in the magnetic system. The quantized quasiparticles are called magnetons, and each magneton carries a Planck constant spin angular momentum. Compared with spin-polarized conduction electrons in traditional metals, spin-wave based magnetons have the following advantages: (1) The transfer of magnetons has no heat dissipation and low damping characteristics, and spins at long distances. There are significant advantages in the dissemination of information; (2) The fluctuation properties of magnetons have both amplitude and phase characteristics, which can break through the logic and computational architecture of the traditional von Neumann system, and may become post-Moore era information transmission. One of the important ways of processing is; (3) Macroscopic quantum effects such as superfluid, superconductivity, Bose-Einstein condensate, and Josephson based on magnetism have also become hot spots in condensed matter physics. In the study of magnetic spintronics, microwave is the most commonly used excitation and detection method. However, the size of microwave devices is difficult to achieve miniaturization. Therefore, to apply magnetic spin devices to semiconductor-scale integrated circuits, there is an urgent need to develop magnetization spin excitation, modulation, and detection methods based on electrical methods.

From 2012 to 2016, the research team led by Han Xiufeng, the State Key Laboratory of Magnetics at the National Institute of Physics, Chinese Academy of Sciences/National Center for Condensed Matter Physics, China, used a magnetron sputtering technique combined with a high-temperature heat treatment process to pass a series of samples. The preparation and optimization overcome the limitation that YIG can only be prepared on single-crystal GGG substrates. The Pt/YIG/Pt heavy metal/magnetic insulator/heavy metal ¬(HM/MI) was designed and prepared on Si-SiO2 substrate. /HM) layered heterostructures, and for the first time observed in the structure by the team of Professor Zhang Yifeng of the University of Arizona, the magnetic drag effect was predicted by the theory, that is due to the excitation and transmission of the magnetons in the YIG, one side of the Pt layer The charge/spin flow can drag the opposite charge/spin flow in the other side Pt layer. This work confirms that the magnetic insulator can act as a transmission channel for magnet spins

Recently, Han Xiufeng's research team has innovatively adopted YIG magnetic insulators as magnetic electrodes, Au as an intermediate layer, and heteroepitaxial growth on GGG substrates to produce high-quality YIG/Au/YIG novel magnetic insulators/metals/ Magnetic Insulator (MI/NM/MI) - Magneto-valve structure, and the first observation and discovery of the Magnon Valve effect in this structure, that is, the orientation of the relative magnetization direction of two magnetic insulation layers can be controlled Magnetic flux size. First, they fine-tuned the crystal structure of two layers of YIG to produce different coercive forces to achieve an anti-parallel relative magnetization orientation; a local current heating method was used to generate a temperature gradient, and a longitudinal spin Seebeck effect was used to stimulate YIG's The magnetic flux, through the magnetic sub-valve's magnetic sub-stream, can realize electrical measurement through the anti-spin Hall effect in Pt; then it finds the magnetic sub-valve effect, that is, the relative orientation of the two-layer YIG can be controlled through the Magnetohydrodynamic flux size of the magnetic valve, wherein the relative magneto-valve ratio (MVR) of the flat and anti-parallel state at the room temperature can reach 19%; and it reveals that the ratio of the magnetic valve ratio mainly depends on the magnetic insulator/ The temperature dependence of the conversion efficiency of the magnetron-electron spin at the metal interface is consistent with the theoretical calculation result; the spin diffusion of Au is obtained by fitting the dependence of the ratio of the magnetic subvalve and Au thickness. The length is 15.1 nm, which is consistent with the results obtained by the spin pump method [Hao Wu and XF Han et al., Phys. Rev. Lett. 120 (2018) 097205, DOI: https://doi.org/10.11 03/PhysRevLett.120.097205, Editors’ Suggest & Featured in Physics].

The YIG/Au/YIG, the new magnetic insulator/mid layer/magnetic insulator (MI/NM/MI) magnetic valve structure prepared by this research work is itself a spin information transfer and logical operation. The basic magnetic-type core cell device is also the material and physical basis for future research and development of magnetic sub-devices based on magnetic sub-stream circuits, logic, storage, diodes, transistors, waveguides, and switches. It shows that a new class of spintronics core devices with magnetic insulators as spin-information carriers in magnetic insulators has important application prospects, and breakthroughs in materials, physics, and devices will potentially accelerate low-energy, rewritable, The birth of new non-volatile and high-frequency computer series core devices. And this magnetic valve structure can be matched with the existing large-scale integrated circuit process, which contributes to the future integrated integration and extensive utilization of magnetic sub-devices, spintronic devices and semiconductor microelectronic devices.