Magnetometry Data Research Articles

Zn1−xCoxSe: A new diluted magnetic semiconductor grown by molecular beam epitaxy

We have grown single-crystal epilayers of the new diluted magnetic semiconductor Zn1−xCox Se on GaAs(001) substrates by molecular beam epitaxy. X-ray θ-2θ and double-crystal rocking curve measurements were used to obtain the variation in lattice parameter and evaluate crystalline quality. Temperature-dependent electron paramagnetic resonance and superconducting quantum interference device magnetometry data confirm the substitutional nature of the Co2+ in the zinc site and paramagnetic behavior.

Magnetic and crystallographic characterization of Zn0.78Fe0.22Se and FeSe films on GaAs (001)

We have grown single-crystal (001) epilayers of the diluted magnetic semiconductor Zn1−xFexSe with 0≤x≤1 on GaAs(001) substrates by molecular-beam epitaxy. The films retain the zinc-blende structure for thicknesses up to at least 2 μm for x≤0.22, while epilayers with higher Fe concentrations can be stabilized up to some decreasing critical thickness. SQUID magnetometry data obtained for x=0.22 indicate Van Vleck paramagnetic behavior accompanied by a decrease in the fraction of magnetically free Fe2+ ions with increasing x. Conversion electron Mössbauer spectra of the FeSe epilayers show a dominant paramagnetic central peak at both 300 and 13.5 K, with small contributions from Zeeman-split components at low temperature. The samples were further characterized with x-ray rocking curve, θ-2θ, and topography measurements.

Properties of Fe single-crystal films grown on (100)GaAs by molecular-beam epitaxy

Single-crystal (100)Fe films 90–330 Å thick have been grown on etch-annealed (100)GaAs substrates by molecular-beam-epitaxy techniques. Ferromagnetic resonance data indicate that the two in-plane 〈110〉 directions are inequivalent and, together with magnetometry data, show that the average film magnetization decreases as the thickness decreases. The inequivalence is attributed to the nature of the interface bonding at a (100) zinc-blende surface. The decreased magnetization is attributed to the formation of Fe2As microclusters in the film due to As diffusion which is supported by Auger and electron diffraction studies. In general, the Fe films grown to date on etch-annealed (100)GaAs substrates are significantly inferior to those grown on (110)GaAs.

Determination of the magnetic anisotropy of ferrofluids from torque magnetometry data

A theoretical analysis is presented which enables the uniaxial magnetic anisotropy constant K 1 of particles in ferrofluids, frozen in an external field, to be obtained from torque magnetometry measurements. The two-fold symmetry of the torque curve, found experimentally, is correctly predicted. An asymptotic solution is found which enables K 1 to be determined without recourse to iterative numerical methods. In this limit, the torque amplitude varies linearly with the inverse of the freezing field for large freezing fields. For all cases, extraction of K 1 requires an accurate knowledge of the particle size distribution parameters.

A comparison of solar flare incidence with magnetic transients observed in the near-by interplanetary region by Pioneer 5

A study of magnetometry data collected from solar satellite Pioneer 5 is described, showing that the temporal fluctuations in ambient field magnitude that characterized the data were correlated in time with the occurrence of moderate to strong Hα flare activity on the visible solar disk. The results of efforts to identify specific flare-disturbance pairs and to calculate propagation velocities from them are included, the minimal size of effective flares appearing to be three to five square degrees in area, and corresponding sun to satellite velocities falling in the range 750 to 1140 km/sec. It is found that some field perturbations, apparently flare-induced and detectable outside the magnetosphere but near the earth, could not be correlated with any apparent effect on the surface geomagnetic field, that disturbance vectors were probably not confined to any single quasi-radial orientation with respect to the sun, and that disturbance amplitudes, which varied between 50 and 500 microgauss, may be directly related to the size of their originating flares.