Influence of interdiffusion on the magnetic properties of Co/Si (100) films after high magnetic field annealing

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Highlights

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    Interdiffusion of Co/Si (100) films by high magnetic field annealing was studied.

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    Thickness of the diffusion layer was reduced by magnetic field annealing at 400 °C.

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    Interdiffusion coefficient decreased following magnetic field annealing at 400 °C.

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    Saturation magnetization increased after high magnetic field annealing at 400 °C.

Abstract

The influence of interdiffusion on the magnetic properties of Co/Si (100) films after thermal annealing in the presence of a strong magnetic field was investigated. The interdiffusion coefficients of films that were annealed at temperatures of 380 °C and 420 °C in the presence of high magnetic fields were not affected. However, the interdiffusion coefficient of films annealed at 400 °C in the presence of a high magnetic field decreased significantly. The change in the interdiffusion coefficient, caused by high magnetic field annealing, increased the content of the magnetic phase. This increase in the magnetic phase improved the saturation magnetization. A new method of high magnetic field annealing is presented that can modulate the diffusion and magnetic properties of thin films.

Introduction

Metal–semiconductor interfaces have received much attention over the last few decades, particularly in the rapidly developing field of spintronics and tunneling effect [1], [2], [3]. To achieve a higher density, devices that incorporate semiconductors are made on nanometer scales. Investigation of the magnetic properties of metal/semiconductor structures has recently drawn much attention for this purpose [4], [5]. There are different methods used to manipulate the magnetic properties of thin films; however, magnetic field annealing has received particular attention [6], [7], [8]. Recent studies on thin films have shown that the use of a high magnetic field during annealing can affect the magnetic properties by influencing the microstructure, phase transformation, and phase segregation [9], [10], [11]. These phenomena are often governed by diffusion. Thus, controlling and understanding interfacial diffusion in thin films and semiconductors are critical as the diffusion distances are close to the thicknesses and feature widths of thin films [12], [13]. The interdiffusion between a Co/Ni bilayer was demonstrated to increase when a high magnetic field was applied during annealing after deposition [14]. Therefore, high magnetic field annealing is a useful tool for controlling the diffusion process.

There are numerous studies on how magnetic fields affect interdiffusion in bulk materials; however, there are a few reports on the influence of high magnetic fields on interdiffusion within metal film/semiconductor systems during annealing. Cobalt is commonly used in magnetic recording media and silicon is the most important substrate in the semiconductor industry. As such, we have investigated the effects of high magnetic field annealing on interdiffusion, and how this affects the magnetic properties of Co/Si (100) films.

Section snippets

Experimental procedure

Polycrystalline Co layers (99.994%) were deposited onto Si (100) substrates at an ambient temperature using molecular beam vapor deposition [15]. The pressure of the vacuum chamber was 2.5×10−4 Pa during the deposition process. The Co thickness was maintained at 130±2 nm as measured by an alpha-step IQ profilometer with a vertical resolution of 0.75 nm. Before Co deposition, the Si (100) substrates were cleaned sequentially in acetone and alcohol baths using ultrasonication. To study the

Phase composition

XRD profiles of the Co/Si (100) thin films when annealed in the presence and absence of a 4 T magnetic field are shown in Fig. 1. The annealed films had hcp structures, indicating that compound phases were not present. However, there was a broad peak at 55° in some samples, indicating that substrate information was sometimes obtained when using a small grazing incidence angle.

The peaks observed in the X-ray spectra were broad. Plausibly, this may be because of grain refinement in the samples.

Conclusions

The influence of interdiffusion on the magnetic properties of Co/Si (100) films, caused by high magnetic field annealing, was investigated. The application of a high magnetic field to Co films when annealed at 400 °C promoted the transformation of the hcp structure to an fcc structure. The smaller interdiffusion coefficients of the fcc phase led to a decrease of the interdiffusion coefficients of Co films exposed to a 4 T magnetic field during annealing. The observed changes in the magnetic

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (Grant nos. 51101032, 51425401) and the Fundamental Research Funds for the Central Universities (Grant nos. N140902001, N140901001, N130509002).

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