Far-infrared magnetotransmission of YBa2(ZnxCu(1-x))3O(7-d)

Measurements of the far infrared magnetotransmission of YBa2(ZnxCu(1-x))3O(7-d) thin film (x = 0.025) deposited on a wedged MgO substrate are reported. The application of magnetic field perpendicular to the ab plane produces at low temperature a linear increase of transmission for frequencies below 30 cm-1. We present a model of high frequency vortex dynamics which qualitatively explains these results.Comment: 2 pages with 2 figures, presented on LT2

Low temperature electrical properties of magnetite and Mn-ferrites

Electrical resistivity and thermoelectric power measurements have been made on single crystals of manganese ferrites, MnxFe3-xO4 (x=0, 0.5, 0.7, 0.8, 0.9, and 0.95) in the temperature range 10 K to 300 K. Below the Verwey transition Tv of magnetite, the thermoelectric power is strongly influenced by the oxygen nonstoichiometry of the samples whereas the resistivity exhibits hardly any dependence on the changes of the oxygen content. Starting from the lowest temperatures, the electrical properties are explained in terms of the impurity band, variable range hopping, small polaron band, and small polaron hopping conduction mechanisms where the long-range and the short-range orderings have to be taken into account

Faraday rotation spectra of bismuth-substituted ferrite garnet films with in-plane magnetization

Single crystalline films of bismuth-substituted ferrite garnets have been synthesized by the liquid phase epitaxy method where GGG substrates are dipped into the flux. The growth parameters are controlled to obtain films with in-plane magnetization and virtually no domain activity, which makes them excellently suited for magnetooptic imaging. The Faraday rotation spectra were measured across the visible range of wavelengths. To interprete the spectra we present a simple model based on the existence of two optical transitions of diamagnetic character, one tetrahedral and one octahedral. We find excellent agreement between the model and our experimental results for photon energies between 1.77 and 2.53 eV, corresponding to wavelengths between 700 and 490 nm. It is shown that the Faraday rotation changes significantly with the amount of substituted gallium and bismuth. Furthermore, the experimental results suggest that the magnetooptic response changes linearly with the bismuth substitution.Comment: 15 pages, 6 figures, published in Phys. Rev.

Spin canting across core/shell Fe3O4/MnxFe3−xO4 nanoparticles

Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin configurations is important for optimizing these applications. The measured magnetization of MNPs can be significantly lower than bulk counterparts, often due to canted spins. This has previously been presumed to be a surface effect, where reduced exchange allows spins closest to the nanoparticle surface to deviate locally from collinear structures. We demonstrate that intraparticle effects can induce spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm diameter, core/shell Fe3O4/MnxFe3−xO4 MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy, x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular magnetic correlations, suggesting multiparticle coherent spin canting in an applied field. Atomistic simulations reveal the underlying mechanism of the observed spin canting. These show that strong DMI can lead to magnetic frustration within the shell and cause canting of the net particle moment. These results illuminate how core/shell nanoparticle systems can be engineered for spin canting across the whole of the particle, rather than solely at the surface

Low temperature electrical properties of magnetite and Mn-ferrites

Electrical resistivity and thermoelectric power measurements have been made on single crystals of manganese ferrites, MnxFe3-xO4 (x=0, 0.5, 0.7, 0.8, 0.9, and 0.95) in the temperature range 10 K to 300 K. Below the Verwey transition Tv of magnetite, the thermoelectric power is strongly influenced by the oxygen nonstoichiometry of the samples whereas the resistivity exhibits hardly any dependence on the changes of the oxygen content. Starting from the lowest temperatures, the electrical properties are explained in terms of the impurity band, variable range hopping, small polaron band, and small polaron hopping conduction mechanisms where the long-range and the short-range orderings have to be taken into account

Effect of heat treatment on the ultrasonic attenuation on Mn-ferrites

The acoustic losses in single crystals of manganese ferrites were studied in the temperature range from 180 to 650 K by applying longitudinal vibrations of 150 kHz. Loss peaks were observed at 232 and 537 K with activation energies of 0.3 and 0.8 eV, respectively. The first loss peak at 232 K is regarded as a stress-induced relaxation of electrons between two and three-valent ions. The second peak at 537 K is ascribed to the exchange motion of iron cations and their vacancies on octahedral sites. Heat treatments at 300 and 600°C affect the oxygen stoichiometry and distribution of cations between octahedral and tetrahedral sites which results in the changes of the loss peaks magnitudes

Magnetic permeability behavior in single crystal Mn-ferrites

Measurements of the initial permeability mu of single crystal ferrites MnxFe3-xO4 with

Magnetic and acoustic relaxations in Mn-ferrites

Magnetic and acoustic losses were measured in single-crystal manganese ferrites at temperatures 80 ÷ 630 K. Relaxation peaks at 230 and 540 K were observed with activation energies of 0.27 ÷ 0.42 and 0.64 ÷ 0.82 eV, respectively. Both peaks are influenced by heat-treatments resulting in different degrees of inversion and vacancy distributions