Magnetic phase transition in Co/Cu/Ni/Cu(100) and Co/Fe/Ni/Cu(100)

Magnetic phase transitions in coupled magnetic sandwiches of Cu/Co/Cu/Ni/Cu(100) and Cu/Co/Fe/Ni/Cu(100) are investigated by photoemission electron microscopy. Element-specific magnetic domains are taken at room temperature to reveal the critical thickness at which the magnetic phase transition occurs. The results show that a coupled magnetic sandwich undergoes three types of magnetic phase transitions depending on the two ferromagnetic films' thickness. A phase diagram is constructed and explained in the process of constructing Monte Carlo simulations, which corroborate the experimental results.     

Angular dependence of auger electron emission from Cu (111) and (100) surfaces

Experimental angular emission profiles of the M_2,3M_4,5M_4,562 eV Cu Auger electrons from clean copper (100) and (111) surfaces in several azimuths are presented. A simple single scattering theory to account for elastic scattering of the Auger electrons by other ion cores in the solid is presented, and calculations have been performed to assess the importance of this process in contributing to the observed angular dependence. These calculations produce angular structure having a similar magnitude and temperature dependence to that observed experimentally, and some featural similarity in peak positions or shapes. It appears that elastic scattering is an important source of angular dependence, and that studies of adsorbed species on surfaces should provide a very sensitive method of surface structure determination.     

Bifurcation magnetic resonance in type (100) films upon in-plane magnetization

The magnetization dynamics in (100) single-crystal films with a cubic anisotropy has been studied by numerical simulation. It has been shown that the additional (bifurcation) resonance caused by the bistability, i.e., two closely spaced equilibrium magnetization states, appears upon in-plane magnetization along the hard axis. The change in the resonance region and the corresponding dynamic regimes with a variation in the RF field or with a small detuning of the magnetizing field has been investigated. The regular and chaotic precession regimes near the bifurcation resonance have been revealed. The states of dynamic bistability have been found.     

Structure and magnetization of (100) FeCr and FeV films deposited on Pd/Cu/Si(100)

(100) oriented FeCr and FeV films, 1000 Å thick, have been deposited on (100)Si using (100)Pd/Cu seed layers. Three compositions are made for each alloy, 75/25, 50/50 and 25/75, all show lattice spacings corresponding to a body-centered cubic structure. Magnetic measurement shows composition dependent magnetization: both FeCr and FeV with compositions of 75/25 and 50/50 are ferromagnetic, but not the ones with the composition of 25/75. In-plane magnetization along different crystalline axes shows the same crystalline anistropy as that of bulk Fe crystal for both 75/25 structures, with a higher magnetization along the [100] edge than the [110] one. For the 50/50 structures, the [100] edge shows a smaller magnetization at low fields than the [110] one, but exceeds the latter at higher field. The measured magnetizations are less than those from linearly diluted Fe lattices. The correlation between the structures and magnetic properties is discussed.     

Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high-mobility (100) Si-inversion layers

We report studies of the magnetoresistance (MR) in a two-dimensional electron system in (100) Si-inversion layers, for perpendicular and parallel orientations of the current with respect to the magnetic field in the 2D plane. The magnetoresistance is almost isotropic; this result does not support the suggestion of its orbital origin. In the hopping regime, however, the MR contains a weak anisotropic component that is nonmonotonic in the magnetic field. We found that the field, at which the MR saturates, varies for different samples by a factor of 2 at a given carrier density. Therefore, the saturation of the MR cannot be identified with the complete spin polarization of free carriers.     

Antiferromagnetic coupling between Co/Ni multilayers with perpendicular magnetization across MBE-grown Cu(111) layers

A cleat oscillatory exchange coupling has been observed for an epitaxial (111) M₁/Cu/M₂ structure, grown by Molecular Beam Epitaxy (MBE) on a single crystal Cu(111) substrate. The magnetic layers M₁ and M₂ were designed to have perpendicular easy axis by using Co/Ni multilayers. The Cu layer was deposited in the form of a wedge. The magneto-optically measured hysteresis loops show, in the case of antiferromagnetic (AF) coupling, clear first-order spin-flip transitions between the saturated and antiparallel states. Signatures of a ferromagnetic or biquadratic component, observed earlier in loops of an AF coupled Co/Cu/Co(111) sandwich, were absent in the present loops. The absence of these signatures is believed to be a consequence of the relatively strong (perpendicular) uniaxial anisotropy of the present samples.     

Angular resolved L3VV Auger emission spectra from Cu(100)

The angular intensity distribution of electron induced L₃VV Auger electron emission from a Cu(100) crystal has been measured. Angular positions of relative maxima in the distribution are aligned with prominent crystallographic directions suggesting strong diffraction effects.     

PLEED studies of the temperature dependence of the surface vs bulk magnetization of Ni(110)

The temperature dependence of the bulk and surface magnetization of Ni(110) is derived using the molecular field theory. These results are then used in a dynamical polarized low-energy-electron-diffraction (PLEED) calculation to yield the temperature dependent polarization of the diffracted intensities, which is compared with recent experimental data for 0.6 T_Curie ≤ T ≤ T_Curie. The importance of multiple scatterings and the usefulness of PLEED for surface magnetic structural determination are clearly demonstrated.     

SHG investigations of the magnetization of thin Ni and Co films on Cu(001)

Received: 22 November 1998     

On the reorientation transition in Cu(100)/Ni n /H

Using the results of a previous study in terms of the scalar-relativistic full- potential linearized augmented-plane-wave method, the fully relativistic screened Korringa-Kohn-Rostoker approach is applied in order to describe the shift in the critical thickness for the so-called inverse reorientation transition from in plane to perpendicular in Ni films on Cu(100) upon loading with H. It is argued that, on average, by loading with H the interlayer distances in the Ni films would have to be reduced by about 3% or, expressed in absolute distances by about 0.05 A, compared with the bare systems, to cause the critical thickness to decrease from about 10 monolayers (ML) for the bare systems to about 8ML for completely H-covered Ni films. Calculations with statistically partial coverages with H and for a complete diffusion of H in the first Ni layer convincingly support this view.     

Temperature dependence of the magnetization of canted spin structures

Numerous studies of the low-temperature saturation magnetization of ferrimagnetic nanoparticles and diamagnetically substituted ferrites have shown an anomalous temperature dependence. It has been suggested that this is related to freezing of canted magnetic structures. We present models for the temperature dependence of the magnetization of a simple canted spin structure in which relaxation can take place at finite temperatures between spin configurations with different canting angles. We show that the saturation magnetization may either decrease or increase with decreasing temperature, depending on the ratio of the exchange coupling constants. This is in agreement with experimental observations.     

Magnetic hyperfine fields in ultrathin Ni films on Cu(100)

The magnetic hyperfine field was measured at ¹¹¹In(¹¹¹Cd) probe atoms in ultrathin Ni films epitaxially grown on Cu(100) utilizing the perturbed -angular correlation (PAC) method. The behaviour of the hyperfine field as a function of temperature was studied for different film thicknesses ranging from 2 up to 10 monolayers. It was found that the strength of the hyperfine fields as well as the critical temperatures are strongly reduced for thin nickel films and approach the bulk value with increasing film thickness. The orientation of the hyperfine field is discussed.     

The photon angle dependence of photoemission from a Cu(100) crystal

The symmetry properties of direct interband transitions are shown to have important consequences for angle-resolved u.v. photoemission. Predictions are made regarding the photon incidence angle dependence of Ar I (11.7 eV) excited photoemission from a Cu(100) single crystal surface, and these are shown to be in close agreement with the experimental results.