Magnetic properties and thermal stability of Co/HfN multilayer films for high-frequency application

Y Cao,S Ohnuma,H Masumoto,Y W Zhang,N Kobayashi

doi:10.1063/1.4983402

Y Cao, S Ohnuma + Show 3 more

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https://doi.org/10.1063/1.4983402

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Abstract

Sputtered metal–nonmetal granular films tend to exhibit growth-induced perpendicular magnetic anisotropy. In this work, Co/HfN multilayers were synthesized to suppress the development of columnar clusters along the deposition direction. The results reveal that a HfN interlayer thickness of less than 0.4 nm is insufficient to separate the columnar clusters; however, increasing the interlayer thickness to 0.8 nm with increasing the sputtering duration successfully led to typical in-plane magnetic anisotropy with a coercivity as low as 3 Oe. The Co(4 nm)/HfN(1.5 nm) multilayers exhibited high permeability of approximately 260 up to 1.6 GHz. The resonance frequency increased from 1.8 to 2.3 GHz with increasing annealing temperature, which is attributed to the increased magnetic anisotropy. Our results suggest that the multilayers still show high-frequency performance even after annealing at 450 °C, which would be a big advantage for complementary metal–oxide–semiconductor (CMOS) fabrication technology.

Highlights

The increasing demands for miniaturization in electromagnetic devices such as transformers, inductors, and other devices over the past few decades have created an increased demand for soft magnetic nano-granular thin films with high electrical resistivity (ρ), large saturation magnetization (Ms), appropriately large magnetic anisotropy field (Hk), and excellent high-frequency characteristics.1–3 The granular films with nanometer-sized ferromagnetic granules dispersed in an insulating matrix display a variety of multifunctional properties, e.g., magnetoresistance4 and magnetoelectric5 and soft ferromagnetic effect.6 Theoretically, the magnetic softness achieved by reduced magnetocrystalline anisotropy can be explained by the random anisotropy model.7 sputtered granular films tend to exhibit perpendicular magnetic anisotropy (PMA) because of the growth-induced columnar structure of the magnetic granules
We observed the transition between PMA and IMA by carefully controlling the thicknesses of each layer; the results suggest that the both the thickness of the Co and HfN layers play essential roles in changing the magnetostatic properties
(2) Under increasing T a, we observed an increase of ferromagnetic resonance frequency (1.8 –2.3 GHz) and a decrease of μ [260–170] owning to the increase in Hk

Summary

INTRODUCTION

The increasing demands for miniaturization in electromagnetic devices such as transformers, inductors, and other devices over the past few decades have created an increased demand for soft magnetic nano-granular thin films with high electrical resistivity (ρ), large saturation magnetization (Ms), appropriately large magnetic anisotropy field (Hk), and excellent high-frequency characteristics. The granular films with nanometer-sized ferromagnetic granules dispersed in an insulating matrix display a variety of multifunctional properties, e.g., magnetoresistance and magnetoelectric and soft ferromagnetic effect. Theoretically, the magnetic softness achieved by reduced magnetocrystalline anisotropy can be explained by the random anisotropy model. sputtered granular films tend to exhibit perpendicular magnetic anisotropy (PMA) because of the growth-induced columnar structure of the magnetic granules. Sputtered granular films tend to exhibit perpendicular magnetic anisotropy (PMA) because of the growth-induced columnar structure of the magnetic granules. Various insulating materials including native oxides such as iron oxide, oxide ceramic and polymers could be used as an interlayer to suppress the PMA and control the high-frequency magnetic properties. While insertion of interlayer was observed to be of great significance for the fabrication of a soft magnetic multilayer structure, relevant studies on the interlayer-controlled transition between PMA and IMA are still limited.. We attempted to control the transition between PMA and IMA by depositing the Co/HfN multilayers with careful variation of thicknesses of the Co layer and HfN interlayer and recorded its high-frequency performance under post-annealing conditions. It is noteworthy that our previous studies have reported growth-induced perpendicular anisotropic Co–HfN nano-granular films.

EXPERIMENTAL

Effect of Co layer and HfN interlayer thickness on the magnetic properties

CONCLUSION