We report an accurate method for the measurement of the saturation magnetostriction λs of thin conducting ferromagnetic films using spin valve structures. We describe an alternative to the cantilever beam method, called the bending method, which utilizes the inverse magnetostrictive effect. Typical soft ferromagnetic films exhibit hysteretic magnetization loops, which make the measurements of the magnetoelastic energy (hence λs) imprecise or erroneous. We show how to resolve the hysteresis problem by application of a transverse field. We also demonstrate the quantitative connection between the cantilever and bending method in a comparative study of films spanning a large magnetostriction range. The sensitivity of measurement of magnetostriction using the bending method is better than 1×10−7.
The magnetic and corrosion properties of Ir16Mn84 with Ru and Cr additions have been studied. Spin valves with Ir16Mn84–Ru have slightly lower Hex and Tb than when pure Ir16Mn84 is used. The corrosion properties improve, Hex and Tb improve with 3 vol % Cr, but drop considerably with more Cr additions, losing 21% of the pure IrMn value by 12 vol % Cr. The corrosion current and potential are Ic=8 μA/cm2 and E0=−580 mV respectively, for Ir16Mn84 with 12 vol % Cr. This represents a significant improvement over pure Ir16Mn84, which has Ic=100 μA/cm2 and E0=−1300 mV. When Ru is used as the additive, Ic and E0 are 10 μA/cm2 and −100 mV, respectively, for 9 vol %. Cr is the superior additive, especially in small concentrations where it shows a significant decrease in the Ic without degrading the magnetic properties.
We have investigated the vortex dynamics of ͑K,Ba͒BiO 3 single crystals below the vortex liquid/glass transition. The activation energy U extracted from transport measurements presents a crossover from a J Ϫ(T) to a ln(J) behavior. The latter expression has been attributed to the existence of a glass transition regime which extends over a large part of the J-T phase diagram. We show that the temperature dependence of U lies entirely in (T): close to transition, the vortex glass structure is prevailing (→0.2), but becomes negligible at low temperature where creep effects may be controlled by the elastic properties of the vortex lattice (→1). The magnetic-field dependence of U is also discussed.
The nature of pinning has been investigated in the three-dimensional
high-Tc
superconductor (K,Ba)BiO3. We show that the magnetic-field dependence of
the
critical current deduced from pulsed-field magnetization measurements can be
well described by the collective-pinning theory on a large temperature range
0.06 < T/Tc < 0.62. This permits us to construct a nonequilibrium
H-T
phase diagram including both
the single-vortex and vortex bundle regimes. Furthermore, the temperature
dependence of the collective-pinning length Lc is in excellent
agreement with
a model of flux pinning induced by spatial fluctuations of the critical
temperature (δTc pinning model).
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