A quantum model for the magnetic multi-valued recording

We have proposed a quantum model for the magnetic multi-valued recording in this paper. The hysteresis loops of the two-dimensional systems with randomly distributed magnetic atoms have been studied by the quantum theory developed previously. The method has been proved to be exact in this case. We find that the single-ion anisotropies and the densities of the magnetic atoms are mainly responsible for the hysterisis loops. Only if the magnetic atoms contained by the systems are of different (not uniform) anistropies and their density is low, there may be more sharp steps in the hysteresis loops. Such materials can be used as the recording media for the so-called magnetic multi-valued recording. Our result explained the experimental results qualitativly.Comment: 10 pages containing one Table. Latex formatted. 5 figures: those who are interested please contact the authors requiring the figures. Submitted to J. Magn. Magn. Mater. . Email address: [email protected]

Quantum model for magnetic multivalued recording in coupled multilayers

In this paper, we discuss the possibilities of realizing the magnetic multi-valued (MMV) recording in a magnetic coupled multilayer. The hysteresis loop of a double-layer system is studied analytically, and the conditions for achieving the MMV recording are given. The conditions are studied from different respects, and the phase diagrams for the anisotropic parameters are given in the end.Comment: 8 pages, LaTex formatted, 7 figures (those who are interested please contact the authors requring the figures) Submitted to Physal Review B. Email: [email protected]

A relativistic magnetron-type source of nanosecond-length pulsed radiation in the 8 mm waveband

The paper describes an up-graded facility for studying performance of a high voltage pulsed magnetron of the 8 mm operation waveband. A pulse forming driving source of high output impedance is offered, yielding voltage amplitudes up to 40 kV and pulse durations about 25 ns, which provides for matching of the liquid-filled pulse forming line with the magnetron and lack of hydraulic strains. As a result, operation of the magnetron is stabilized and reproducibility of the output parameters greatly increased.Наведено результати модернізації установки для дослідження робочих режимів високовольтного імпульсного магне-трона діапазону 8 мм. Запропоноване і створене нове високоомне джерело формування імпульсів, що мають значення напруги до 40 кВ і тривалості до 25 нс. Джерело живлення, що було запропоноване, забезпечує узгодження лінії формування імпульсів з магнетроном і відзначається відсутністю гідравлічних ударів. Як результат маємо підвищення стабільності роботи магнетрона, покращення керованості режимами роботи і відтворення результатів.Представлены результаты модернизации установки для исследования рабочих режимов высоковольтного импульсного магнетрона диапазона 8 мм. Предложен и создан новый высокоомный источник формирования импульсов напряжением до 40 кВ и длительностью 25 нс, обеспечивающий согласование линии формирования импульсов с магнетроном и отсутствие в ней гидравлических ударов. В результате повышена стабильность работы магнетрона, управляемость его режимами и воспроизводимость результатов

Low-variance black-box gradient estimates for the Plackett-Luce distribution

Learning models with discrete latent variables using stochastic gradient descent remains a challenge due to the high variance of gradient estimates. Modern variance reduction techniques mostly consider categorical distributions and have limited applicability when the number of possible outcomes becomes large. In this work, we consider models with latent permutations and propose control variates for the Plackett-Luce distribution. In particular, the control variates allow us to optimize black-box functions over permutations using stochastic gradient descent. To illustrate the approach, we consider a variety of causal structure learning tasks for continuous and discrete data. We show that our method outperforms competitive relaxation-based optimization methods and is also applicable to non-differentiable score functions

Characterization facility for magneto-optic media and systems

Objectives of this research are: (1) to measure the hysteresis loop, Kerr rotation angle, anisotropy energy profile, Hall voltage, and magnetoresistance of thin-film magneto-optic media using our loop-tracer; (2) measure the wavelength-dependence of the Kerr rotation angle, Theta(sub k), and ellipticity, epsilon(sub k), for thin-film media using our magneto-optic Kerr spectrometer (MOKS); (3) measure the dielectric tensor of thin-film and multilayer samples using our variable-angle magneto-optic ellipsometer (VAMOE); (4) measure the hysteresis loop, coercivity, remanent magnetization, saturation magnetization, and anisotropy energy constant for thin film magnetic media using vibrating sample magnetometry; (5) observe small magnetic domains and investigate their interaction with defects using magnetic force microscopy; (6) perform static read/write/erase experiments on thin-film magneto-optic media using our static test station; (7) integrate the existing models of magnetization, magneto-optic effects, coercivity, and anisotropy in an interactive and user-friendly environment, and analyze the characterization data obtained in the various experiments, using this modeling package; (8) measure focusing- and tracking-error signals on a static testbed, determine the 'feedthrough' for various focusing schemes, investigate the effects of polarization and birefringence, and compare the results with diffraction-based calculations; and (9) measure the birefringence of optical disk substrates using two variable angle ellipsometers

Monte Carlo Simulation of Magnetization Reversal in Fe Sesquilayers on W(110)

Iron sesquilayers grown at room temperature on W(110) exhibit a pronounced coercivity maximum near a coverage of 1.5 atomic monolayers. On lattices which faithfully reproduce the morphology of the real films, a kinetic Ising model is utilized to simulate the domain-wall motion. Simulations reveal that the dynamics is dominated by the second-layer islands, which act as pinning centers. The simulated dependencies of the coercivity on the film coverage, as well as on the temperature and the frequency of the applied field, are very similar to those measured in experiments. Unlike previous micromagnetic models, the presented approach provides insight into the dynamics of the domain-wall motion and clearly reveals the role of thermal fluctuations.Comment: Final version to appear in Phys. Rev. B. References to related works added. 7 pages, 5 figures, RevTex, mpeg simulations available at http://www.scri.fsu.edu/~rikvol