The magnetization switching behavior in a nanostructured magnetic thin film, under combined in-plane fields along the longitudinal and the transverse directions, is investigated both analytically and numerically. Two critical curves under a static and a dynamic condition are calculated analytically by using an equation for the total energy. The analytically calculated critical curves are compared with the micromagnetic simulation results for the switching phase diagrams of nonswitching, incoherent switching, and coherent switching. The comparison indicates that the dynamic critical curve is the boundary separating the nonswitching from the incoherent switching, while the static critical curve acts as the boundary between the incoherent switching and the coherent switching. The present results indicate that the switching phase diagram can be constructed analytically with the use of a total energy equation. The analytically calculated critical curves are less accurate in the presence of the simplifying assumptions of a single and in-plane domain state for a small angle between the applied magnetic field and the easy axis. In this case, an accurate value of the anisotropy energy, an input to the total energy equation, must be accurately estimated by micromagnetic simulation.
Theoretical equations were derived for the resonance frequency of magnetization oscillation in a nanostructured synthetic ferrimagnet in the framework of a single domain model. The theoretical equations, which are applicable to various magnetization alignments including a spin flop, were then tested using a micromagnetic simulation in both the macrospin and microspin models. Excellent agreement was obtained between the results of the theoretical prediction and micromagnetic simulation in the macrospin model over the entire range of applied magnetic fields, confirming the validity of the theoretical equations derived in this study. The agreement between the results from the theoretical prediction and the micromagnetic simulation in the microspin model was not excellent, particularly in the acoustic mode, showing a substantial deviation from the ideal single domain behaviour. However, good agreement was obtained by decreasing the magnetization component in the thickness direction by 10% of that in the single domain state. This suggests that the magnetization deviates slightly from the single domain state as the magnetization moves out of the film plane during a magnetization oscillation.
The volatile anesthetics may reduce cardiac contractility by limiting both membrane Ca2+ entry and altering intracellular Ca2+ release. Additional pharmacological effects of calcium channel blockers could potentially enhance anesthetic-induced depression. The aim of this study was to compare the direct cardiac effects of enflurane and a new volatile anesthetic, desflurane, in combination with diltiazem on the isolated Sprague-Dawley rat heart.After stabilization period isolated rat hearts (n = 40) were perfused with an oxygenated modified Krebs' solution at 55 mmHg equilibrated with 1, 2 and 3 MAC of enflurane (1.7, 3.4 and 5.1 vol% respectively) or desflurane (6, 12 and 18 vol% respectively) in combination with 100 ng/mL diltiazem at 36 degrees C. Isovolumetric left ventricular pressure (LVP), rate of change of ventricular pressure (dp/dt), spontaneous heart rate and coronary flow were measured. To examine the indirect metabolic effect due to autoregulation of coronary flow, O2 delivery (DO2), myocardial O2 consumption (MVO2) and percent O2 extraction (POE) were also monitored.Diltiazem plus enflurane or desflurane depressed LVP and dp/dt dose-dependently. Enflurane plus diltiazem significantly decreased heart rate more than desflurane plus diltiazem in a dose-dependent manner. Desflurane plus diltiazem significantly increased coronary flow more than enflurane plus diltiazem and oxygen delivery increased proportionally with coronary flow. But there were statistically insignificant dose-dependent increases in both groups. Myocardial oxygen consumption and percentage of oxygen extraction were also decreased dose-dependently in both groups. Bradydysrhythmia that accompanied atrioventricular dissociation occurred with diltiazem plus high enflurane or desflurane concentration at an incidence of 46% and 40% respectively.These in vitro results demonstrate that diltiazem plus enflurane or desflurane depresses left ventricular contractile function and diltiazem plus enflurane causes higher incidence of bradydysrhythmia more than equivalent levels of diltiazem plus desflurane.
A magnetization switching method for magnetic random access memory (MRAM), recently proposed by Savtchenko et al. [U.S. Patent No. 6,545,906 (2003)], is known to have an important advantage of a wide window for bit writing over the conventional method based on the asteroid curve, but it has a serious problem of high switching fields. In an effort to solve this problem, the effects of the thickness asymmetry and antiferromagnetic exchange coupling of the synthetic antiferromagnetic free-layer structure on the switching field have been investigated by micromagnetic computer simulation. At conditions relevant to high-density MRAM, magnetization switching in the direct write mode occurs at reasonably low values of word- and bit-line fields (below 100Oe), combined with a substantially wide window for bit writing. A much wider window is observed in the toggle mode, but the required switching fields are too high, being over 150Oe.
The static and microwave magnetic properties of soft nanogranular (Fe0.7Co0.3)71B22Ni films with a 2T saturation magnetization are presented as functions of thickness, ranging from 136to235nm. Microwave permeability values from 60 to 260 are measured and ferromagnetic resonance frequencies up to 6.8GHz are found using a vector network analyzer, connected to coplanar/microstrip structures loaded with the ferromagnetic films. Topographic and magnetic structures down to 20–40nm were observed by atomic/magnetic force microscopy. The combination of reasonable values of the permeability and high ferromagnetic resonance frequency makes these nanogranular materials useful in the development of inductive microwave components.
Abstract Artificial interface anisotropy is demonstrated in alternating Co/Pt and Co/Pd stripe patterns, providing a means of forming magnetic anisotropy using lithography. In-plane hysteresis loops measured along two principal directions are explained in depth by two competing shape and interface anisotropies, thus confirming the formation of interface anisotropy at the Co/Pt and Co/Pd interfaces of the stripe patterns. The measured interface anisotropy energies, which are in the range of 0.2–0.3 erg/cm 2 for both stripes, are smaller than those observed in conventional multilayers, indicating a decrease in smoothness of the interfaces when formed by lithography. The demonstration of interface anisotropy in the Co/Pt and Co/Pd stripe patterns is of significant practical importance, because this setup makes it possible to form anisotropy using lithography and to modulate its strength by controlling the pattern width. Furthermore, this makes it possible to form more complex interface anisotropy by fabricating two-dimensional patterns. These artificial anisotropies are expected to open up new device applications such as multilevel bits using in-plane magnetoresistive thin-film structures.
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