Crystallographic and magnetic structure of RbCoCl3 · 2 D2O

The crystallographic and magnetic structure of RbCoCl3 · 2 D2O were determined mainly by means of neutron diffraction measurements. Below TN = 2.79 K the magnetic moments are ordered in a canted antiferromagnetic pattern. A meta-magnetic phase transition is observed at unusually small field values (H = 18 Oe at T = 2 K)

Influence of the FM/AFM interface morphology on the exchange coupling in epitaxial Co(001)/fct-Mn(001)

The Co thickness dependence of the exchange interaction between ferromagnetic (FM) fct-Co(001) and antiferromagnetic (AFM) fct-Mn(001) thin layers, epitaxially grown on Cu(001) single crystals, was studied. In the pseudomorphic Co growth regime, oscillations of the coercivity (HC) and the exchange bias (HE) with a Co at. monolayer period are obsd. These oscillations are explained by a biquadratic exchange interaction component at the FM/AFM interface which, in this thickness range, is modulated by the layer-by-layer growth mode of Co on Cu(001). [on SciFinder (R)

Monolayer resolved oscillating hyperfine fields in epitaxial face-centered-tetragonal Co(001) films

Ultrahigh-quality thin fct-Co films grown on Cu(001) were studied by 59Co NMR. The influence of the spin-dependent electron scattering at the interfaces is obsd. for at least four Co at. layers from the interface with monolayer resoln. An oscillatory effect on the Co hyperfine field with a period of several monolayers is measured, corresponding to the oscillating conduction electron polarization. The observation is exclusively possible in this system due to its very narrow resonance lines, corresponding to a virtually perfect Co structure. [on SciFinder (R)

Electric-field gradients in thin face-centered-tetragonal Co films observed by nuclear magnetic resonance

Thin tetragonally strained fcc-Co films grown epitaxially on Cu(001) single crystals have been investigated by 59Co nuclear magnetic resonance (NMR). The ultrahigh structural quality and the homogeneity of the strain result in the direct NMR observation of electric-field gradients, which is unique in thin films. The structural quality and the homogeneity and size of the strain are analyzed by means of the very small NMR linewidths, the hyperfine field anisotropies, and the uniform electric-field gradients. A quantitative agreement with the observed strain is found. The strain, and thus the tetragonal distortion, in the films is found to be surprisingly stable, showing less than 10% strain relief for 80 ML Co films

Formation of nonmagnetic c-Fe_{1-x}Si in antiferromagnetically coupled epitaxial Fe/Si/Fe

Low-energy electron diffraction, Auger electron spectroscopy, and conversion electron Mössbauer spectroscopy have been applied to study antiferromagnetically exchange-coupled epitaxial Fe/Si/Fe(100). It is shown that a bcc-like (100) structure is maintained throughout the layers after a recrystallization of the spacer layer by Fe/Si interdiffusion. Direct experimental evidence is presented that c-Fe1-xSi (

Analysis of scattering lengths in Co/Cu/Co and Co/Cu/Co/Cu spin-valves using a Ru barrier

We use uncoupled Co/Cu/Co and Co/Cu/Co/Cu spin-valve structures with a Ru barrier shifted through the top Co and Cu layer, respectively, to measure the longest of the electron mean free paths in Co and Cu as originally suggested by Parkin. From semiclassical transport calculations and careful analysis of the magnetoresistance data we conclude that the exponential behavior of ¿G is uniquely related to the longest of the Co and Cu mean free paths under the condition of effective spin-dependent filtering at the interfaces or in the bulk of the Co. In this regime we have compared ¿long in Co and Cu with bulk conductivities (~¿short+¿long), yielding no strong evidence for bulk spin-dependent scattering in Co

Change of the barrier potential shape in magnetic tunnel junctions due to an anneal treatment

A very important process step in the fabrication of magnetic tunnel junctions (MTJs) is the application of a modest anneal step in the presence of a high magnetic field. Roughly, a doubling of the magnetoresistance (MR) ratio is commonly observed. We show that both AlOx as well as TaOx MTJs with Co90 Fe10 electrodes have similar oxidation time and anneal temperature dependencies of the MR ratios. In both cases, the maximum MR ratio shifts to higher oxidation times with annealing. TaOx MTJs are, in this sense, good model systems. From photoconductance experiments we find that for TaOx MTJs, this shift in maximum MR is accompanied by a similar shift of the zero crossing of the oxidation time dependent barrier asymmetry. This directly supports the point of view that for obtaining the highest MR ratio one should anneal MTJs that would be characterized as "slightly overoxidized" in the as-deposited state. We argue that this result can be understood by a homogenization of the oxygen distribution in the barrier, andor a change of the bottom barrier-electrode interface. © 2005 American Institute of Physics

Specific heat of ZnCoSe semimagnetic semiconductor

The magnetic specific heat of ZnCoSe data are reported in the temperature range 1.5 <T <50 K and magnetic field B <3 T. The experimental data are interpreted in the Extended Nearest Neighbour Pair Approximation taking into account short and long ranged d-d exchange interaction

Analysis of breakdown in ferromagnetic tunnel junctions

Due to their very thin tunnel barrier layer, magnetic tunnel junctions show dielectric breakdown at voltages of the order of 1 V. At the moment of breakdown, a highly conductive short is formed in the barrier and is visible as a hot spot. The breakdown effect is investigated by means of voltage ramp experiments on a series of nominally identical Co/Al2O3/Co tunnel junctions. The results are described in terms of a voltage dependent breakdown probability, and are further analyzed within the framework of a general model for the breakdown probability in dielectric materials, within which it is assumed that at any time the breakdown probability is independent of the (possibly time-dependent) voltage that has been previously applied. The experimental data can be described by several specific forms of the voltage breakdown probability function. A comparison with the models commonly used for describing thin film SiO2 breakdown is given, as well as suggestions for future experiments