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We present a study of electronic and magnetic properties of nominal magnetite nanoparticles (NPs) (~6 nm) at high pressure in the presence of silicon pressure medium using x-ray absorption near edge structure (XANES), x-ray magnetic circular dichroism (XMCD) and non-resonant x-ray emission spectroscopy (XES). XANES data show a reduction of Fe charge state, a change in local environment around Fe at tetrahedral sites, and a reduced occupation of Fe 4p orbitals, not seen in previous pressure studies of bulk magnetite. XMCD data show a continuous magnetic moment reduction of ~50% between ambient pressure and 20 GPa, similar to what was observed in previous bulk magnetite studies. XES spectra of NPs indicate a gradual change in spin configuration away from the high-spin state consistent with a postulated charge transfer from Fe 4p to 3d states and the observed reduction in XMCD signal. Taken together, the results point to substantial differences in the response of electronic and magnetic properties of the nano-counterparts of bulk magnetite at high pressure.

An avalanche photodiode detector has been commissioned to measure weak resonant x-ray magnetic scattering (RXMS) from induced magnetic polarizations in Cu layers in exchange-coupled Co/Cu multilayers using circularly polarized x-rays from synchrotron sources. The detector can count x-rays at rates of 10 7 photons s −1 ,g iving good estimates of the RXMS at superlattice Bragg peaks in a reasonably short time when count losses due to the time structure of the synchrotron x-rays are corrected for. RXMS superlattice Bragg peaks as small as 1 × 10 −4 in flipping ratio have been measured from aC o/Cu multilayer at the K absorption edge of Cu. The data are fitted by an oscillatory model magnetization profile in the Cu layers derived from a Ruderman–Kittel–Kasuya–Yosida theor yo fe xchange coupling adapted to a planar geometry.

A nanoscopic fluctuational dynamic model is suggested for observed anomalous reversible changes of the M?ssbauer isomer shift (ARCOMIS) found recently in Ag-Sn alloys not affected by long ageing. The model considers fluctuation-induced nanoscale large transient atomic displacements (LTADs) and material disordering. They cause electron localization, taking place simultaneously and permanently in the nanometre vicinities of M?ssbauer impurity atoms in the entire alloy. This causes an additional enhancement in the electron charge density |?f(0)|2 at the M?ssbauer nuclei, leading to the ARCOMIS at temperature Ts. These phenomena are generated by persistent sequences of nanoscale short-lived (picosecond) large energy fluctuations (SLEFs) of atomic particles of the peak thermal energy 0p>?E>>kT, which occur simultaneously and constantly in the material. The model leads to the following results. (i)?A SLEF-mediated dynamic mechanism for the ARCOMIS occurring at relatively low temperatures Ts is proposed. (ii)?The temperature Ts(Ag-Sn)?500?K is calculated, in good agreement with observations. (iii)?The narrow temperature interval ?T 3% is suggested. (vi)?An explanation is offered for the absence of the ARCOMIS in SnO2 material. (vii)?Similar results are obtained for the Au-Sn alloys not affected by long ageing, in good agreement with tentative experimental data.

The position of the Mossbauer resonant absorption line of was measured at various temperatures and concentrations of substitutional Sn impurities in the -phase of the Ag-Sn alloy. Whereas 1.0 and 2.0 at.% Sn alloys showed the expected temperature dependence of the line shift (LS), 4.0 and 8.0 at.% Sn alloys showed several anomalous features. After aging at room temperature (RT) for several months, these alloys showed hysteresis of the LS from RT up to about 500 K. At about 520 K, the unusual slope transforms to its expected value but continues with an increased isomer shift (IS). Further thermal cycles resulted in the expected slope of the LS with no measurable hysteresis, except for the transition region around 520 K above which the IS increase persisted. The experiments indicate that after thermal cycling the high-concentration alloys are in an intermediate state below about 500 K, which becomes metastable at RT as shown by the changes with aging. The transition to the increased-IS state at , however, is independent of the thermal history. A discussion of the observed phenomena is presented, which is based on thermally induced changes in the Sn-Sn distribution (short-range order) that preserve the long-range order of the alloy.