Three-dimensional magnetic recording using ferromagnetic resonance

Abstract

To meet the ever-increasing demand for data storage, future magnetic recording devices will need to be made three-dimensional by implementing multilayer recording. In this article, we present methods of detecting and manipulating the magnetization direction of a specific layer selectively in a vertically stacked multilayer magnetic system, which enable layer-selective read and write operations in three-dimensional magnetic recording devices. The principle behind the methods is ferromagnetic resonance excitation in a microwave magnetic field. By designing each magnetic recording layer to have a different ferromagnetic resonance frequency, magnetization excitation can be induced individually in each layer by tuning the frequency of an applied microwave magnetic field, and this selective magnetization excitation can be utilized for the layer-selective operations. Regarding media for three-dimensional recording, when layers of a perpendicular magnetic material are vertically stacked, dipolar interaction between multiple recording layers arises and is expected to cause problems, such as degradation of thermal stability and switching field distribution. To solve these problems, we propose the use of an antiferromagnetically coupled structure consisting of hard and soft magnetic layers. Because the stray fields from these two layers cancel each other, antiferromagnetically coupled media can reduce the dipolar interaction.

Three-dimensional nanomagnetism

“…Future studies are expected in laterally patterned nanostructures, to investigate the effect of rotating fields and dipolar interactions on the domain formation and soliton operation 71 72 . The use of different mechanisms for propagation, such as spin-transfer torque 73 , microwave excitations 74 or all optical switching 75 , are also anticipated. Additionally, a new energy storage concept based on the continuous injection of solitons via the rotation of one edge spin in a cork-screw fashion, has been recently proposed 63 .…”

Layer-selective detection of magnetization directions from two layers of antiferromagnetically-coupled magnetizations by ferromagnetic resonance using a spin-torque oscillator

“…In this work, however, we assume a single STO for simplicity. The MD has two AFC-RLs, each of which consists of a soft layer (SL) and a hard layer (HL) [2,8]. We refer to the upper layer as RL1 and the lower layer as RL2.…”

“…Ferromagnetic resonance (FMR) has long been studied as a subject of fundamental physics as well as a tool for observing the magnetic states of materials and devices. Recently, the use of FMR has been proposed for three-dimensional (3D) (or multilayer) recording to increase recording density in hard disk drives (HDDs) [1][2][3][4][5][6][7][8][9][10]. The use of FMR enables layer-selective writing [1][2][3][4][5][6][7] and reading [1,2] by employing recording layers (RLs) with different FMR frequencies and then selectively inducing FMR by using a microwave field of the corresponding frequency.…”

Zero-dc-field rotation-direction-dependent magnetization switching induced by a circularly polarized microwave magnetic field

“…Furthermore, the use of FMR excitation can provide novel techniques for manipulating magnetization direction. One is layer-selective MAS, which has been explored as a writing method for multilayer recording 7 , 8 . When a multilayer magnetic structure with each layer having a different FMR frequency is used, switching of only a target layer can be selectively induced by tuning the frequency of the microwave field.…”