Temperature Dependence Of Hc Research Articles

Effect of backing on temperature dependence of thin-film magnetic properties

Results are given from studies of temperature dependence of Hc and Hk for thin permalloy films. It is shown that the character of Hc and Hk temperature variation is to a significant degree determined by the difference in temperature-expansion coefficients of film and backing, and also by the magnitude and sign of magnetostriction λs.

Magnetic properties of assemblies of single domain elliptical platelets

Magnetization and remanence loops for a uniform spatial distribution of noninteracting single domain thin discs of elliptical shape are calculated. It is found that the relative remanence of such a system has magnitude 0.638. The temperature dependence of hc and hR is investigated and found to be approximately linear over a temperature range depending upon the particle volumes and anisotropy. The values of hc and hR are found to be 0.562 and 0.648 at T=0K, respectively. The results are compared with those obtained for a uniform distribution of uniaxial particles.

Switching Properties of Europous Oxide

Measurements of quasistatic and dynamic switching properties of EuO have been made. EuO was pressed in the form of toroidal cores, and fired at different temperatures to obtain a variety of grain sizes. The quasistatic switching properties measured at 4°K with a 105 cps drive field (H<100 Oe) show that the hysteresis loop is not square and the remanent magnetization Mr is typically 60% of saturation value. The coercivity Hc was shown to decrease with increasing grain size. For example, with a grain size increase from 55 to 220 μ, Hc decreases from 13 to 10 Oe (with H=50 Oe). Hc also decreases with decreasing drive field. The temperature dependence of Hc is similar to that of M but decreases at a slower rate for temperatures up to 63°K. The dynamic switching properties, when expressed in τ(H–H0) = S (τ is the switching time, H is the applied field, H0 is the threshold field, and S is the switching coefficient), of a typical sample with Hc=5 Oe (at H=30 Oe) are τ(H−20) = 2.5 μsec·Oe for H≥70 Oe and τ(H−12) = 3.1 μsec·Oe for H≤70 Oe at 4.2°K for 90% switching. At low field, the flux reversal appears to be dominated by domain-wall motion; at high field the flux may reverse by nonuniform rotation. In contrast to conventional ferrite materials, EuO has slower switching speed and, consequently, has few application possibilities as computer storage elements. However, the large value of M coupled with nonsquare hysteresis loop and the insulating property make this material attractive for use in a number of low-temperature applications.