查看更多>>摘要：This article introduces a global approach to magnetic topology optimization for hard magnetic materials, aiming to achieve a specific stray field distribution. The proposed method utilizes a hybrid optimization algorithm that integrates the strengths of both local and global optimization techniques. The ideas, advantages, and disadvantages of each approach are discussed in detail and tested and illustrated using selected model problems. The results show that global optimization approaches are necessary to achieve significantly lower minima of the objective function, since multiple local minima might occur for such problems and the outcome of local optimization methods highly depends on the chosen starting configurations.
查看更多>>摘要：Pt/Co/Pt trilayers with perpendicular magnetic anisotropy (PMA) were deposited onto Si substrates with Cu seed layers, which were thermally annealed at various temperatures to alter their surface roughness. Annealing at temperatures up to $475~^{\circ }$ C induced significant grain growth in the 5 nm thick Cu seed layer, substantially increasing its surface roughness. At $500~^{\circ }$ C, the root-mean-square (rms) roughness of the Cu seed layer surpassed the 0.8 nm thickness of the Co layer, potentially disrupting its continuity. This increased surface roughness created pinning sites that significantly enhanced coercivity—up to approximately 430% compared to the as-deposited trilayer—by impeding domain wall motion. However, the excessive roughness at $500~^{\circ }$ C weakened ferromagnetic exchange interactions between Co spins, diminishing PMA and coercivity. Magnetic domain images revealed that the increasing Cu layer roughness promoted the formation of new domain nucleation sites while reducing domain wall velocity. These findings demonstrate that the perpendicular magnetic properties of the Pt/Co/Pt layer can be controlled by the microstructural characteristics of the underlying seed layer.
查看更多>>摘要：We use the direct simulation Monte Carlo (DSMC) method along with the consistent Boltzmann algorithm (CBA) to study the environmental factors affecting smear formation in a representative heat-assisted magnetic recording (HAMR) air bearing. We focus on the humidity, temperature, density, and velocity fields due to the high-temperature hotspot on the head-disk interface. We find that the gas temperature gradient in the vertical direction is significantly smaller than that expected by the temperature difference between the head and disk surfaces. This is possible since the head-disk clearance limits the mean free path of the gas bearing. Consequently, the velocity field of the gas in the vertical direction also showed a drift from the colder to the hotter surface at low spacing. We also observed a high partial pressure of water vapor in the gas bearing, several times higher than the ambient level due to the higher gas temperature and pressure.
查看更多>>摘要：A control-oriented mathematical model for single-phase transformers, including the effects of saturation, hysteresis, and classical eddy current losses, is proposed. The model equations are derived by combining the mechanical and electrical properties of the ferromagnetic transformers’ core. This approach offers the flexibility for model enhancement by providing a procedure for incorporating additional domain-specific effects. It is shown that the model satisfies well-established properties of systems with hysteresis. The model is mathematically analyzed and experimentally validated on different transformers, confirming the applicability for a wide range of devices. Furthermore, it is demonstrated that the model structure is independent of any specific choice of the input signal form by reproducing experimental results for both sinusoidal and rectangular excitation voltages. The proposed model is compared with a single-phase transformer model based on the well-recognized Jiles-Atherton hysteresis model, which generally highlights the competitiveness in terms of accuracy and required computational effort for simulation studies. Therefore, the model is well suited for model-based controller design tasks and real-time applications.
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NSTL
IEEE