Effect of seedlayer and junction geometry on permanent magnet stabilization of magnetoresistive heads
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The dependence of CoPt stabilization properties on surface topography and seedlayer thickness has been investigated. The coercivity degrades drastically without a Cr seed, showing a dependence upon surface angle. Using the resulting data wafer level sensor structures are micromagnetic simulated. Poor seedlayer coverage on the junction edge yields open transfer curve loops and degraded sensor response.Keywords:
Micromagnetics
The coercivity of anisotropic cast–hot-pressed Pr19Fe74.5B5Cu1.5 magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation-controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: iHc(kOe) = 21.7550 − 6.0517 ln d (μm), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5 magnets exhibit a much lower coercivity due to their coarse-grained cast structure.
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It has been a puzzle for a century about how ``hard'' (coercive) a ferromagnet can be. Seven decades ago, W. Brown gave his famous theorem to correlate coercivity of a ferromagnet to its magnetocrystalline anisotropy field. However, the experimental coercivity values are far below the calculated level given by the theorem, which is called Brown's Coercivity Paradox. The paradox has been considered to be related to the complex microstructures of the magnets in experiments because coercivity is an extrinsic property that is sensitive to any imperfections in the specimens. To date, coercivity cannot be predicted and calculated by quantitative modeling. In this investigation, we carried out a case study on the high magnetic coercivity of Co nanowires exceeding the magnetocrystalline anisotropy field as predicted by Brown's theorem. It is found that the aspect ratio and diameter of the nanocrystals have a strong effect on the coercivity. When the nanocrystals have an increased aspect ratio, the coercivity is significantly higher than the magnetocrystalline anisotropy field of a hcp Co crystal. Micromagnetic simulations give a coercivity aspect-ratio dependence that is well consistent with the experimental results. It is also revealed that a coercivity limit exists based on the geometrical structures of the nanocrystals that govern the demagnetizing process. The quantitative correlation obtained between the structure and coercivity enables material design of advanced permanent magnets in the future.
Magnetocrystalline anisotropy
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Films of Co-P, varying in composition from 2.5% to 5% P and varying in thickness from 200 to 2500 Å, were prepared by chemical deposition. The coercivity of these films was found to be a function of both P content and thickness. The particle size of these films increased with increasing thickness and was a function of the P content. The films were annealed in a reducing atmosphere at various temperatures up to 500°C. The low-coercivity films undergo a transformation to films exhibiting coercivities of ∼250 Oe at a temperature of 250°C. The intermediate-coercivity films remain essentially unchanged, whereas the high-coercivity films drop sharply in coercivity at ∼400°C to this apparent ``equilibrium coercivity'' of ∼250 Oe. Etching experiments on these samples show no drastic effects on coercivity. The coercivity merely proceeds back along the original coercivity-versus-thickness curves. Structural and magnetic evidence indicates the existence of an equilibrium magnetic structure in these films which is primarily dependent on particle size.
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Strain (injury)
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The nature of domain-wall motion coercivity in magnetic media is studied using a two-dimensional numerical micromagnetic model. It is necessarily assumed that the source of the coercivity is cylindrical anomalies in the material that have anisotropy or exchange parameters which are either larger or smaller than that of the surrounding media. Varying these parameters from those required to obtain the observed coercivity shows that a larger decrease in either parameter is required to obtain the same change in coercivity as a given increase. Thus, the dependence of coercivity on these parameters is nonlinear. It was also found that the computed coercivity decreases with an increase in the separation of the defects, and increases with an increase in defect size. It is shown that a correction for the calculated coercivity is required to account for the statistical distribution in defect sizes and locations. Finally, a suitable variation in the defect parameters can accurately characterize the temperature behavior of the coercivity.
Recording media
Single domain
Domain wall (magnetism)
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Magnetocrystalline anisotropy
Aspect ratio (aeronautics)
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In the present paper, the angular dependence of coercivity for the Sm2Fe17Cx magnets has been investigated in detail. Our results indicate that the angular dependence of the coercivity depends strongly on the coercivity value of the sample. For the sample of low coercivity with short ball milling time, the coercivity increases at first, develops a peak and then decreases with increasing angle between the easy axis and the direction of the external field. In contrast, minimum coercivity behavior has been observed in the sample of larger coercivity with longer ball milling time.
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The magnetoresistance response of cobalt nanocontacts with varying geometries formed between two extended electrodes has been experimentally investigated and linked to micromagnetic simulations. The contribution of the nanoconstriction to the measured magnetoresistance signal has been separated from that of the electrode bulk. The different nanocontact geometries exhibit different shape anisotropies resulting in a characteristic behavior of the magnetization at each nanocontact. The magnetization reversal processes are explained on the basis of the anisotropic magnetoresistance and domain wall scattering effects. The domain wall resistance takes positive values, which is in agreement with models based on the spin mistracking inside the domain wall.
Micromagnetics
Domain wall (magnetism)
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In the present paper, the angular dependence of coercivity for the Sm2Fe17Cx magnets has been investigated in detail. Our results indicate that the angular dependence of the coercivity depends strongly on the coercivity value of the sample. For the sample of low coercivity with short ball milling time, the coercivity increases at first, develops a peak and then decreases with increasing angle between the easy axis and the direction of the external field. In contrast, minimum coercivity behavior has been observed in the sample of larger coercivity with longer ball milling time.
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