D. I. Kholin

Control of Interlayer Exchange Coupling in Fe=Cr=Fe Trilayers by Ion Beam Irradiation

The manipulation of the antiferromagnetic interlayer coupling in epitaxial Fe/Cr/Fe(001) trilayers by 5 keV He ion beam irradiation has been investigated. It is shown that even for irradiation with low fluences a drastic change in strength of the coupling appears. For thin Cr spacers (below 0.6-0.7 nm) it decreases with fluence, becoming ferromagnetic for fluences above 2x10(14) ions/cm(2). The effect is connected with the creation of magnetic bridges in the layered system due to atomic exchange events caused by the bombardment. For thicker Cr spacers an enhancement of the antiferromagnetic coupling strength is found. A possible explanation of the enhancement effect is given.

Spin-glass state of Fe/Cr multilayer structures with ultrathin iron layers

The evolution of the magnetic properties of Fe/Cr superlattices with a decrease in the nominal thickness of the iron layers down to atomic dimensions at which these layers are not continuous has been analyzed. Investigations have been carried out with multilayer samples with Fe-layer thicknesses in a range of 2–6 Å and Cr-layer thicknesses of 10 and 20 Å. It has been found that the system with various Fe-layer thicknesses and at various temperatures exhibits various magnetic phases—superparamagnetic, magnetically ordered, and nonergodic—characterized by the dependence of the magnetization of the sample on its magnetic prehistory. It has been shown that the observed nonergodic phase has the properties of a spin glass. A qualitative phase diagram of the magnetic states of the system has been obtained.

Interlayer interaction in a Fe/Cr/Fe system: Dependence on the thickness of the chrome interlayer and on temperature

A three-layer sample of Fe(100 Å)/Cr(0–20 Å)/Fe(100 Å) is used to study the dependence of inter-layer exchange on the thickness of the chrome interlayer and on temperature. The method of Kerr magnetometry in the temperature range from 77 to 473 K and the method of Brillouin scattering of light by spin waves at room temperature are used. The data for magnetization curves and spin wave spectra are treated in the model of biquadratic exchange. The range of validity of this model is established, which is apparently determined by interlayer exchange. The resultant dependence of the constant of bilinear interaction on the interlayer thickness demonstrates an oscillating behavior with two oscillation periods of about 3 and 18 Å. Within the experimental error, the magnitude of this constant, the amplitude, and the period and phase of its oscillation are independent of temperature. It is found that the constant of biquadratic exchange decreases in inverse proportion to the chrome thickness, the proportionality factor decreasing linearly as the temperature rises. In order to interpret the observed singularities in the behavior of the biquadratic exchange constant, a theoretical model is suggested which includes the nonideality of the interface and the presence of magnetic hardness in the chrome interlayer. This rigidity exceeds in magnitude the interaction on the interface between iron and chrome. The suggested model gives an adequate qualitative description of the experimental results.

Inhomogeneous ferromagnetic resonance modes in [Fe/Cr]n superlattices with a high biquadratic exchange constant

In a set of [Fe/Cr]n superlattices, magnetization curves and spectra of ferromagnetic resonance under an in-plane magnetic field have been studied at room temperature. Along with the acoustic branch, several additional branches have been observed in resonance spectra. Resonance spectra have been calculated analytically for a structure with an infinite number of layers and numerically for finite numbers of layers in real samples using a model of biquadratic exchange taking account of the fourth-order magnetic anisotropy. A possibility of describing both static and resonance properties of the system in terms of this model has been demonstrated.

Ferromagnetic resonance in multilayer [Fe/Cr]n structures with noncollinear magnetic ordering

The excitation spectrum in an [Fe/Cr]n multilayer structure with non-collinear magnetic ordering was studied by the ferromagnetic resonance (FMR) method in the frequency interval 9.5–37 GHz at room temperature. Besides an acoustic branch, several additional modes were observed under parallel excitation of resonance. The FMR spectrum was calculated analytically in a biquadratic exchange model, neglecting in-plane anisotropy, for an infinite number of layers in the structure and numerically for a finite number of layers contained in real samples. It was shown that the observed modes correspond to excitation of standing spin waves with wave vectors perpendicular to the film plane.

The interlayer exchange interaction in multilayer magnetic systems Fe/Cr/Fe (Review Article)

Upsurge of interest in the study of magnetic multilayer structures began in the mid-80s of the twentieth century and was caused by significant progress in the technology of ultrathin metallic films. For a few years, phenomena extremely interesting from both fundamental and applied point of view have been found in these structures: the antiparallel arrangement of the ferromagnetic layers, giant magnetoresistance, alternating oscillations of the interlayer exchange, noncollinear interlayer ordering of magnetic moments. All this and the closeness of technologies, used for the sample preparation to those traditionally applied in microelectronics, promised great potentials for developing compact magnetic field sensors, non-volatile memory for electronic devices, etc. To date, some of these features are already implemented in the mass commercial products (e.g., read heads of hard drives), and others still wait in the wings. The Nobel Prize, awarded in 2007 to A. Fert and P. Grunberg with the words “For the disc...

Magnetic states of multilayer Fe∕Cr structures with ultrathin iron layers

The evolution of the magnetic properties of Fe∕Cr superlattices is studied as the nominal thickness of the iron layers is reduced to atomic values, when these layers are no longer continuous. The studies were done on multilayer samples with Fe thicknesses of 2–6A and chromium spacer thicknesses of 10 and 20A. The samples were prepared by molecular beam epitaxy. The static magnetization and complex magnetic susceptibility were measured and FMR spectra taken. It was found that, depending on the thickness of the Fe layers and temperature, different magnetic phases are realized in the system: supermagnetism, magnetic ordering, and a nonergodic state characterized by a dependence of the magnetization of a sample on its magnetic prehistory. The observed nonergodic phase is found to exhibit spin glass properties. A qualitative phase diagram of the magnetic states of this system is constructed.

Interlayer magnetic coupling in multilayer magnetic Fe/Cr/Fe systems

The interlayer magnetic coupling of iron layers as a function of the chromium spacer thickness and temperature has been studied for three-layer epitaxial Fe/Cr/Fe films by the methods of Kerr magnetometry and Mandelstam-Brillouin scattering. The results obtained indicate that the short-period component of the interlayer exchange is related to the spin density wave in the chromium spacer.

Charge mobility anisotropy in hcp 4He crystals

A strong anisotropy of the positive-charge mobility is observed in hcp 4He crystals. The mobility activation energies in the principal directions are determined.