Modern magnetic materials for memory and EMI shielding application

Abstract

The coming "big data" age has required a large demand of fast and low energy consumption nonvolatile memory. Among which spin-transfer-torque magnetic random-access memory (STT-MRAM) has been considered as the most promising one to reduce energy consumption compared to the current dynamic RAM. This STT-MRAM uses magnetic tunnel junction (MTJ) as memory element and shows low switching current, high thermal stability factor, and high tunnel magnetoresistance ratio. However, conventional magnetic materials with perpendicular magnetic anisotropy (PMA) cannot meet all required criteria. Therefore, large efforts have been put on the development of novel PMA materials for STT-MRAM and control mechanisms in memory devices. The booming development of data and communication technology also generates a large amount of electromagnetic interference (EMI). To address this, various EMI shielding materials have been developed. Due to the limitations on the direct application of magneto-dielectric materials or conventional metal-based materials, the development of ideal EMI shielding materials that are lightweight, construable, thermally stable, and have strong absorption capacities is essential and urgently needed. Firstly, a systematic study of sputtered Mn3Ge films on MgO substrates with various buffer layers is presented. I show that Fe/Pt and Fe seed layers can contribute to improving magnetic properties. This result offers a new concept of high-quality growth of D022-Mn3Ge films, which may enhance the prospect for tetragonal Mn3Ge thin films in superior spin-transfer-torque applications. Secondly, I introduce a phase-change induced control of ferromagnetic resonance of Si/GeSbTe/FeCoB heterostructures. We show that different crystalline phases in GeSbTe/FeCoB films contribute to large shifts in ferromagnetic resonance field of FeCoB by up to 150 Oe. These results introduce a method of phase-change induced control of ferromagnetic resonance which enables ultra-low power consumption voltage control of magnetism. Finally, I propose the fabrication of magnetic wood through an inorganic mineralization method. The result presents that a 3 mm thick magnetic wood shows 5~10 dB (or 7~10×) enhanced electromagnetic wave attenuation across the X-band of 8~12 GHz compared to nonmagnetic wood with the same thickness. This work provides a potential strategy to develop wood-based materials for magneto-optical applications such as EMI shielding.--Author's abstract