Papers by Keyword: Switching Field

Abstract: Decrease of a switching field, H_sw, of the magnetic media with high magnetocrystalline anisotropy constant, K_u, can be handled by tilted-easy axis. Not only tilting easy direction of crystal but also optimum magnetic properties can improve writability. The effects of K_u and saturation magnetization, M_s, of L1₀-CoPt material of BPM with 45° tilted-easy axis are investigated in this article. The object oriented micromagnetic framework package based on Landau - Lifshitz - Gilbert equation has been used to analyze the magnetic properties of media in this paper. The results indicate that the H_sw decreases with decreasing K_u and increasing M_s. To achieve the H_sw lower than the maximum write head field, the K_u and M_s values should not be over 1.30 MJ/m³ and should exceed 0.30 MA/m, respectively.

Abstract: Effects of magnetic material, coating thickness, and tip radius on the magnetic force microscope (MFM) spatial resolution and the switching field have been investigated. MFM tips are prepared by coating soft and hard magnetic materials on non-magnetic Si-base tips. MFM spatial resolutions better than 8 nm are obtained by optimizing the coating layer thickness at around 20 nm on the Si tips with top radius of 3 – 5 nm. The switching field can be increased greater than 1 kOe by coating a high-K_u magnetic material and by increasing the coating thickness. The tips are successfully applied to the observations of magnetic thin films which include magnetization structures less than 20 nm in length.

Abstract: Ultrahigh areal density is the key target of hard disk drive technology. Hence, writing field strength from head and switching field, H_sw, of media should be improved. In this work, we propose the one of alternative method to increase data density and reduce H_sw of the media by using tilted easy axis technology for bit patterned media (BPM) at areal density beyond 2.5 Tb/in². Moreover, transition noise and superparamagnetic limit have been eliminated owing to characteristics of BPM. The effect of exchange coupled between adjacent bits, A_dot, of tilted easy axis of BPM is analyzed by micromagnetic simulation software - the object oriented micromagnetic framework based on Landau-Lifshitz-Gilbert equation. The BPM with tilted easy axis perform clearly the reduction of H_sw below perpendicular media and available writing head field. The A_dot of BPM has no effect on decreasing H_sw. Anisotropy and Zeeman energy density of BPM with tilted easy axis are higher and lower than perpendicular BPM, respectively. Thereby, BPM with tilted easy axis have high potentiality to improve H_sw of media at ultrahigh data density.

Abstract: The L1₀-FePt/Fe based exchange coupled composite (ECC) bilayer media is one candidate to extend the areal density of magnetic recording system and solve writability issue in trilemma. L1₀-FePt is the great high magnetic anisotropy material. Therefore, the magnetic parameters of this material such as magnetocrystalline anisotropy constant, K_u, saturation magnetization, M_s, and exchange coupling between a soft/hard interface, are important on magnetic material properties. In this work, the effects of magnetic parameters on magnetic properties of L1₀-FePt/Fe based ECC bilayer media are simulated by the object oriented micromagnetic framework based on Landau-Lifshitz-Gilbert equation. The ECC bilayer media can reduce switching field, H_sw, of media lower than available writing head field. Hence, writability issues of high K_u media can be achieved. Reducing H_sw of ECC bilayer media obtains from lower K_u and higher M_s values. This work can achieve writing capability of a future magnetic recording system.

Abstract: Magnetic force microscope (MFM) tips are prepared by coating Si tips of 4 nm radius with [Co (1 nm)/M(1 nm)]₂₀ (M = Pt, Pd, Ni) multilayer films. An MFM tip prepared by coating 40-nm-thick Co film is employed as a reference tip. The influences of M layer material on the spatial resolution and the switching field of MFM tip are investigated. The spatial resolutions of Co/M multilayer coated tips are estimated to be within 9.4 ± 0.3 nm for all the M materials, which is about 6% inferior to that of Co coated tip (8.8 nm). Higher switching fields of 1425 and 825 Oe are respectively observed for the tips coated with Co/Pt and Co/Pd multilayers, whereas the field of tip coated with Co/Ni multilayer is 275 Oe which is similar to that of Co coated tip (325 Oe). The switching field is influenced by the magnetic anisotropy of multilayer film. An MFM tip coated with Co/Pt multilayer film is useful to observe the magnetic domain structure of permanent magnets and magnetic recording media.

Abstract: We have studied the influence of the thermal treatment on the stress dependence of the switching field during the devitrification of amorphous Fe_73.5Cu₁Nb₃Si_11.5B₁₁ microwires. The non-destructive test (NDT) method based on the magnetization reversal of ferromagnetic materials is sensible to changes in microstructural characteristics and the stress state of the material. The stress dependence has been explained considering the magnetoelastic contribution to the switching mechanism which is modified applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses distribution through thermal treatments. We show that by properly setting a frequency during the measurement and adequate treatment of the sample, it is possible to vary the sensitivity, magnitude and stress dependence of the sample. Keywords: Magnetic bistability, glass-coated microwires, switching field, stress sensor

Abstract: Effects of magnetic material, coating thickness, and tip radius on magnetic force microscope (MFM) spatial resolution have been systematically investigated. MFM tips are prepared by using an UHV sputtering system by coating magnetic materials on non-magnetic Si tips employing targets of Ni, Ni-Fe, Co, Fe, Fe-B, and Fe-Pd. MFM spatial resolutions better than 9 nm have been confirmed by employing magnetic tips coated with high magnetic moment materials with optimized thicknesses.