Magnetically Soft Co-C Granular-like Amorphous Thin Films With High Resistivity and High Saturation Flux Density
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Magnetically Soft Co-C Granular-like Amorphous Thin Films With High Resistivity and High Saturation Flux Density H. Wang, S.P. Wong, M.F. Chiah, W.Q. Li, C.Y. Poon, W.Y. Cheung, and N. Ke Department of Electronic Engineering and Materials Science and Technology Research Center, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, PR China ABSTRACT Granular-like amorphous CoxC1-x nanocomposite thin films, with x in the range of 60-75% in atomic percentage, have been prepared by pulsed filtered vacuum arc deposition. The structures of the films were characterized by non-Rutherford backscattering spectrometry, transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Raman spectroscopy. The in-plane magnetic hysteresis loops were measured by a superconducting quantum interference device magnetometer at room temperature. The electrical transport properties were measured by the four-probe technique at various temperatures ranging from 20 to 300 K. The films were found to be magnetically soft with coercivities in the range of 2 to 12 Oe, resistivities in the range of 130 to 300 µΩ⋅cm, and magnetic saturation flux densities in the range of 6 to 13 kG. The films also showed good thermal stability in their structural, electrical and magnetic properties upon annealing up to 200oC in a vacuum furnace. INTRODUCTION With the increase of magnetic recording area density, high coercivity media and high data rates are needed. As a consequence, it brings challenges to write head performance to write high coercivity media at high frequencies. The general requirements for thin film head core material are high saturation flux density (Bs) or high moment to generate high field without saturation of the core, low coercivity (Hc) to reduce magnetic hysteresis loss, reasonable high permeability (µ) to be used at high frequency, high resistivity (ρ) to suppress eddy current, high anisotropy (Hk) to eliminate ferromagnetic resonance loss, zero magnetostriction (λs) to ensure the magnetic field not producing stress in the film, high Curie temperature (Tc) to sustain thermal stability, and good corrosion resistance to survive fabrication and file requirements. So far, the core material for commercial write head is electroplated permalloy developed by IBM in 1991 [1]. However, the moderate Bs (9-10 kG) and low ρ (20-25 µΩ⋅cm) may limit its applications in the case of ultra high-density recording. The traditionally only choice of high frequency bulk core material is ferrite for its high ρ value, but it’s not suitable for magnetic integrated circuit and thin film head applications due to the low Bs, low initial µ, and low Tc [2]. FeXN (X=Al, Zr, Ta, V, Ti, W, Hf) films have very high Bs (~20 kG) and poses great potential as write head core materials for ultra high-density magnetic recording applications [3-6]. However, these films have been known to have problems at high frequencies due to the moderate ρ (~100 µΩ⋅cm). The very high Bs (20-21 kG) and near zero λs properties of Co rich CoFe and CoNiFe alloys
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