Magnon bottleneck emergence in La2-xSrxCuO4+δ and its use in studies of the dynamics of CuO2 planes

An improved model of the magnon bottleneck is used to show the possibility of measuring the relaxation rate to a homogeneous magnetization lattice of copper-oxygen planes in copper oxide. The agreement between EPR measurements of the spin dynamical characteristics in CuO2 planes and data obtained by NMR spectroscopy is proven to be adequate. © 1996 American Institute of Physics

FMR studies of CrO2 epitaxial thin films

Epitaxial (100) thin films of CrO2 of various thickness were fabricated by chemical vapor deposition (CVD) at atmospheric oxygen pressure onto (100) TiO2 single-crystal substrates. Ferromagnetic resonance (FMR) measurements were performed at the X-band (9.5 GHz) at room temperature. The angular dependencies of the FMR spectra in both "in-plane" and "out-of-plane" geometries were measured. The directions of easy and hard axes of magnetization were determined from the in-plane measurements, when the DC magnetic field was rotated in the film plane. It was established that, at room temperature, the easy axis of magnetization is parallel to the c-axis of the CrO2 rutile structure. Splitting of the FMR signal into surface and bulk modes was observed due to surface pinning of magnetization at interfaces of the CrO2 films. The magnetoelastic anisotropy was observed to be enhanced with decreasing film thickness. The values of the room temperature effective magnetization and parameters of the anisotropy field were obtained from analysis of the FMR data. © 2003 Elsevier B.V. All rights reserved

Boundary resistance in magnetic multilayers

Quasiclassical boundary conditions for electrochemical potentials at the interface between diffusive ferromagnetic and non-magnetic metals are derived for the first time. An expression for the boundary resistance accurately accounts for the momentum conservation law as well as essential gradients of the chemical potentials. Conditions are established at which spin-asymmetry of the boundary resistance has positive or negative sign. Dependence of the spin asymmetry and the absolute value of the boundary resistance on the exchange splitting of the conduction band opens up new possibility to estimate spin polarization of the conduction band of ferromagnetic metals. Consistency of the theory is checked on existing experimental data.Comment: 8 pages, 3 figures, designed using IOPART styl

On the scalar sector of the covariant graviton two-point function in de Sitter spacetime

We examine the scalar sector of the covariant graviton two-point function in de Sitter spacetime. This sector consists of the pure-trace part and another part described by a scalar field. We show that it does not contribute to two-point functions of gauge-invariant quantities. We also demonstrate that the long-distance growth present in some gauges is absent in this sector for a wide range of gauge parameters.Comment: 15 pages, no figures, LaTeX, considerably shortene

Re-entrant superconductivity in Nb/Cu(1-x)Ni(x) bilayers

We report on the first observation of a pronounced re-entrant superconductivity phenomenon in superconductor/ferromagnetic layered systems. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu(1-x)Ni(x). The superconducting transition temperature T_{c} drops sharply with increasing thickness d_{CuNi} of the ferromagnetic layer, until complete suppression of superconductivity is observed at d_{CuNi}= 4 nm. Increasing the Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at d_{CuNi}=13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.Comment: 3 pages, 3 figures, REVTEX4/twocolum

High curie-temperature ferromagnetism in cobalt-implanted single-crystalline rutile

The ion implantation technique has been used to fabricate a Co-rich layer in rutile: single-crystalline TiO2 substrates were heavily irradiated by Co+ ions with energy of 40 keV. The magnetic properties of as-prepared and post-annealed samples were studied by both inductive and Faraday magnetometry as well as ferromagnetic resonance (FMR). A ferromagnetic Curie temperature as high as 700 K was measured in our samples. The analysis of the magnetic hysteresis loop, the temperature dependence of the saturation magnetization, and strong out-of-plane anisotropy of the FMR spectra allow us to suppose that the origin of the macroscopic high-temperature ferromagnetism is the exchange interaction mediated by oxygen vacancies

Massless Minimally Coupled Fields in De Sitter Space: O(4)-Symmetric States Versus De Sitter Invariant Vacuum

The issue of de Sitter invariance for a massless minimally coupled scalar field is revisited. Formally, it is possible to construct a de Sitter invariant state for this case provided that the zero mode of the field is quantized properly. Here we take the point of view that this state is physically acceptable, in the sense that physical observables can be computed and have a reasonable interpretation. In particular, we use this vacuum to derive a new result: that the squared difference between the field at two points along a geodesic observer's space-time path grows linearly with the observer's proper time for a quantum state that does not break de Sitter invariance. Also, we use the Hadamard formalism to compute the renormalized expectation value of the energy momentum tensor, both in the O(4) invariant states introduced by Allen and Follaci, and in the de Sitter invariant vacuum. We find that the vacuum energy density in the O(4) invariant case is larger than in the de Sitter invariant case.Comment: TUTP-92-1, to appear in Phys. Rev.

On the hyperfine interaction in rare-earth Van Vleck paramagnets at high magnetic fields

An influence of high magnetic fields on hyperfine interaction in the rare-earth ions with non-magnetic ground state (Van Vleck ions) is theoretically investigated for the case of $Tm^{3+}$ ion in axial symmetrical crystal electric field (ethylsulphate crystal). It is shown that magnetic-field induced distortions of $4f$-electron shell lead to essential changes in hyperfine magnetic field at the nucleus. The proposed theoretical model is in agreement with recent experimental data.Comment: 4 pages, no figures, submitted to J. Phys. : Cond. Mat