Frequency and Speed of Action of a Spin Valve with Planar Layer Anisotropy
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Frequency and Speed of Action of a Spin Valve with Planar Layer Anisotropy Iu. A. Iusipova* Institute for Design Problems in Microelectronics, Russian Academy of Sciences, Moscow, Russia *e-mail: [email protected] Received March 26, 2020; revised March 26, 2020; accepted April 2, 2020
Abstract—The dynamics of the magnetization vector of the free layer of a layered spin-valve structure has been simulated. As materials for a free and fixed layer, we have considered six magnetically soft ferromagnets with planar anisotropy. The types of magnetization dynamics being of practical interest for MRAM and HMDD (magnetization vector switching), STNO (stable precession of the magnetization vector), and the PSL base element (magnetization vector switching with two probable results) are allocated. The ranges of currents and fields corresponding to these operating modes of a spin valve are calculated. The numerical calculations of the switching time showed that of the materials considered, the most suitable for a MRAM cell is the Co80Gd20 alloy and Fe60Co20B20 for the HMDD reading head. As a result of calculating the frequency of precession, it was concluded that the Fe60Co20B20 alloy is optimal in manufacturing STNO ferromagnetic layers. For PSL implementation, the best switching characteristics were obtained for Co93Gd7 alloy. Keywords: spin valve, random access magnetoresistive memory, probabilistic spin logic, spin-transfer nanooscillator, reading head of the hard drive DOI: 10.1134/S1063783420090358
1. INTRODUCTION In the classical theory, the magnetic states of ferromagnets are controlled by an applied magnetic field. In 1996, Slonczewski [1] predicted another way to change the magnetic configuration of nanomagnets by means of a spin-polarized current. The angular momentum transferred by a spin-polarized current transfers the torque to the magnetization vector, which leads to its switching to a new equilibrium state or the state with constant precession. A change in the projection of the magnetization vector on the anisotropy axis causes a change in the magnetoresistance of the layered spin-valve structure, which entails voltage fluctuations in the external circuit. The simplest configuration of such a structure consists of a relatively thick “fixed” ferromagnetic layer, which serves as a polarizer of current, a nonmagnetic layer and a relatively thin “free” layer. The antiferromagnetic layer is needed to fix the magnetization of the fixed layer. A nonmagnetic metal (e.g., copper) or a thin dielectric (e.g., MgO) are used as a nonmagnetic spacer. Spin-valve structures are applied in a large number of microelectronic devices, such as random access magnetoresistive memory (MRAM) [2, 3], reading heads of hard disks (HMDD) [4], and various spintransfer nanoscillators (STNOs) [5]. They are also used to implement deterministic (SL) [6] and probabilistic spin logic (PSL) [7–12].
A MRAM magnetoresistive memory is a universal memory that can perform the function of an in-circuit programmable memory, fast buffer and non-volati
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