Large anisotropy energy is an essential property of high quality permanent magnets. In previous work we have calculated the spin polarized electronic structure and anisotropy of monolayers and slabs of Fe, Ni, and V. In this work we calculate the dependence on temperature of the spin anisotropy of a ferromagnetic monolayer of Fe. We find the easy direction of magnetization is not sensitive to the temperature; the variations calculated here are likely too small to be observed. It is perpendicular to the plane of the surface for both low and high temperatures. The calculations become progressively more ill-behaved as the temperatures are lowered and require more computer time for satisfactory convergence.

For Fe/Cu {100}, we find the spins always prefer to point out of plane. Experimental results in general are consistent with this view, although the systems seem to be difficult to prepare.

We have succeeded in producing high quality (110)Fe/(111)Ag superlattices by Molecular Beam Epitaxy. Important parameters in the production of these materials were substrate temperature and effusion rates of the constituents. We have used SQUID magnetometry, Mössbauer spectroscopy and Reflection High Energy Electron Diffraction to demonstrate flatness and continuity of the films down to a thickness of approximately 2 atomic layers for the iron and 5 atomic layers for the silver. In the case of the thinnest iron layers, no large reduction of the ferromagnetic Curie temperature was observed, although this had been suggested and reported by other investigators. Furthermore, there was no indication for this particular growth system that the magnetization of the iron was out of the plane of the film. Variations of the magnetic hyperfine fields observed in the iron films were seen both as a function of iron thickness and as a function of the thickness of the intervening silver layers. For the thinnest films, the temperature dependence of the magnetization showed a linear behavior rather than the traditional T3/2 form.

We have made a study of magnetic heterostructures involving the epitaxial growth of (110)Fe on (111)Ag. The flatness and continuity of the films was verified by Reflection High Energy Electron Diffraction during the growth process. A series of structures were made with very thin intervening silver layers with thicker iron layers. The doping of appropriate layers by enriched Fe57 made it possible to examine the magnetic structure of the iron films as a function of depth. Preliminary results indicate that thin layers of silver sandwiched between two very thin Fe layers are able to transmit conduction electron polarization, resulting in iron behavior which resembles that of bulk iron. Implications of these results for understanding the nature of the magnetization of iron will be addressed in the following.

X-band magnetic resonance has been used to study a set of Fe/ Ag(001) superlattice (SL) samples with Fe layers only 0.9–5.5 monolayers (ML) thick. The samples (grown by MBE and previously examined by Mossbauer and magnetization techniques) were studied thoughout the 5–300 K range. The SL's with t(Fe) < 3 ML exhibit a marked downturn in their resonance fields below a temperature which decreases with t(Fe) and, simultaneously, the linewidths increase. We suggest that this behavior is due to magnetic relaxation processes in these samples.

Multilayered films consisting of ferromagnetic Fe and nonmagnetic Al layers were prepared by using ion beam sputtering, and the relationships between their crystallographic characteristics and soft magnetic properties have been investigated in detail.

The periodicity of the multilayered films was confirmed for various layer thicknesses (ΔFe and ΔA1) above 10Å from their X-ray diffraction peaks at low angle. When ΔFe decreased along with ΔA1 from 100Å, the coercivity Hc decreased and showed a minimum of 1.5 Oe at layer thicknesses of 20Å, but at the same time, the saturation magnetization 4πMs which was estimated from total thickness of the Fe layers decreased from 20 kG and showed drastic decrease at ΔFe below 10Å. For ΔFe above 100Å, 4πMs was constant around 20 kG without dependence on ΔA1. When ΔAl was changed for AFe of 100Å, the values of Hc had a interesting relationship with the crystallite orientation in Fe layers. Namely, the preferentially oriented planes of α-Fe crystallites changed from (110) to (200) in the case of Al layer thinner than 15Å and Hc showed a minimum below 4 Oe for ΔAl in this transition range of crystallite orientation, while 4πMs of all Fe layers themselves was kept at 20 kG. Taking into consideration that the nearest atomic distance of fcc Al and the lattice constant of bcc Fe is almost the same, these results may be caused by crystallographical interaction at the interfaces between Fe and Al layers.

This paper presents calculations of hysteresis loops in ferromagnetic multilayer systems of cubic or uniaxial anisotropy with antiferromagnetic coupling between adjacent layers. The case of a bilayer has been systematically studied as a function of the strenght of the anisotropy. The two limiting cases corresponding to either a coherent rotation of the magnetization or to a non-dissipative nucleation-propagation mechanism are investigated. The influence of the number of layers is also discussed.

We recently reported the observation of a very large magnetoresistance in (001)Fe/(001)Cr superlattices grown by MBE. The magnetoresistance is found to be very large for thin Cr layers. We ascribe this magnetoresistance to a magnetic gate effect.

We recently reported the observation of a very large magnetoresistance in (001)Fe/(001)Cr superlattices with thin Cr layers [1]. A large magnetoresitance has also been observed in Fe/Cr/Fe sandwhiches [2]. In both cases, for Cr layers thinner than about 30 Å an antiparallel coupling of the magnetization of neighbor Fe layers is indicated by magnetic, magneto-optic and light scattering measurements [1–3]. It thus turns out that the large magnetoresistance os associated with the change to parallel alignment in an applied field. In this paper, we present new data on the magnetic and transport properties of Fe/Cr superlattics and we concentrate on the discussion of the microscopic origin of the magnetoresistance

Magnetic microstructure, that is the configuration of domains and domain walls in a magnetic material, is of both fundamental interest and of crucial importance for device applications. For example, the ultimate density of magnetic information storage is limited by the sharpness of a domain boundary. The magnetic microstructure of a thin film or surface depends sensitively on its physical structure which is strongly affected by sample preparation or growth. High resolution magnetization imaging is necessary to determine the domain configuration that occurs for a particular sample preparation and the changes that take place under external perturbations such as applied magnetic field, stress or temperature.

The spin dependent energy loss mechanisms in low-energy electron scattering from a ferromagnetic Ni(110) surface are studied. It is shown that exchange scattering can be the dominant loss mechanism for small energy losses. The energy-, angle and temperature dependence of spin asymmetries are studied in detail.

Spin- (and angle-) resolved inverse photoemission spectroscopy (SPIPES) has beenused for studying magnetic thin films. The spin dependence of the unoccupiedelectronic structure has been investigated for in-situ-grown epitaxial, ultrathin Fe and Cofilms on W(001). The Fe overlayers have a square lattice and exhibit in-plane magneticremanence in the direction of the surface Brilluoin zone. Four or more atomic layersof Fe show bulklike SPIPES spectra with a majority spin peak at the Fermi energy (EF)and a broad minority peak 1.3 eV above EF The Co overlayers on W(001) showdistorted hexagonal structures in the plane with an atomic density twice that of theW(001) plane. Two atomic layers of Co show strong in-plane magnetic remanence withthe minority peak at 0.7 eV. The SPIPES results in general are consistent with thetheoretical electronic structure for momentum-conserving radiative transition from freeelectron-like bands down to the unoccupied 3d bands.

Thin (0–6 monolayer) films of gadolinium on Cu(100) have been investigated using synchrotron radiation photoemission. From the definite selection of final state symmetries in photoemission, we have been able to determine a lower bound to the exchange splitting of the gadolinium 5d band. The gadolinium films on Cu(100) exhibit an exchange splitting that changes from approximately 1.1 eV to 0.6 eV as the overlayer thickness increases. The results for thicker films agree with the accepted values for the 5d exchange splitting of bulk gadolinium.

In this review, we show how spin polarized cascade electron spectroscopy provides a relatively rapid and flexible approach to the study of a variety of problems of current interest in both ultrathin magnetic films and surface magnetism. Specific examples relating to the non-bulk like magnetization behavior as a function of temperature of ultrathin films are given which lead to the conclusion that stabilization of the magnetization at low temperature is a universal characteristic of ultrathin magnetic films. Comparison between ultrathin film and surface magnetic behavior is made. Evidence is given that the weakening of exchange coupling both at the surface of a bulk sample and across magnetic spacer layers between an ultrathin magnetic thin film and a bulk sample can be evaluated and dramatic effects due to minute quantities of non-magnetic nearest neighbors are demonstrated.

By using UHV deposition technique, multilayered films consisting of Fe and rare-earth (Dy, Nd or Y) layers were prepared. Magnetic properties of Fe layers were investigated from 57Fe Mössbauer spectroscopy. From SQUID magnetic measurements, the behavior of rare-earth layers was studied. In Fe/Dy and Fe/Nd multilayers, there often exists a large perpendicular anisotropy. Mössbauer spectra evidenced that, in certain samples, the magnetization changes the direction, from in-plane at high temperature to perpendicular at low temperature. The origin of the perpendicular anisotropy is attributed to interface rare-earth atoms which are magnetically coupled with ferromagnetic Fe layers even at higher than their bulk Curie temperatures.

Hexagonal-close-packed Fex/Rux superlattices with the modulation along the (0001) axis, contaln fully hcp Fe layers. The interatomic Fe-Fe distances are enlarged by about 10% as compared to fcc Fe. Ferromagnetic behavior is found when Fe layers are thicker than about 4 monolayers.

Co/Pd multilayers containing one to eight atomic layers of cobalt and ten atomic layers of palladium per modulation period were prepared in two orienotarteiottnoss, [111]fcc and [001]fcc. The [111] films were polycrystalline, the [001] films were epitaxial.

In this paper we compare the magnetic anisotropy of both types of films, which can be described by an interface anisotropy contribution favouring perpendicular magnetization and a volume contribution favouring in-plane magnetization. Depending on the deposition temperature, a perpendicular anisotropy for [111] films is found for up to about six atomic layers of Co. The [001] films however, show perpendicular anisotropy only for Co monolayers or Co bilayers. The large difference between the anisotropies in the two orientations is mainly caused by a strong in-plane anisotropy volume term which exists for [001] films, and which is attributed to the structural deformation of the Co layers from cubic to tetragonal. For both orientations a higher deposition temperature is found to lead to an increase of the interface anisotropy due to smoothing of the layers.

We describe measurements on the structural and magnetic properties of Co–Au superlattices grown on Ge–buffered (110) GaAs by molecular beam epitaxy. Samples have been prepared with Co layer thicknesses ranging from 5–40Å and Au spacer layers of constant thickness, ∼ 16Å. X–ray scattering and high-resolution transmission electron microscopy show that the hcp Co layers grow epitaxially with the (0001) axis parallel to (111)Au and with the in–plane Co[1120] axis parallel to GaAs[001]. SQUID magnetometer measurements reveal a crossover in the magnetic anisotropy of the as–grown samples such that the easy axis is perpendicular to the substrate plane when the Co layer thickness is less than ∼19Å.

The analysis of the magnetization measurements performed on two Co-Cu multilayers confirm the antiferromagnetic coupling already observed with neutron experiments. Both exchange and anisotropy energies are taken into account and estimated. Their competitive role in the individual moment orientation leads to typical moment arrangements and hysteresis loops.

Au/3d-metal(Fe, Co, and Ni) artificial multilayered films were prepared by alternate deposition technique in ultrahigh vacuum. Well defined superstructures were confirmed by transmission electron microscopy and Xray diffraction method. All 3d-metals were epitaxially grown on (111) oriented Au buffer layers. A large perpendicular magnetic anisotropy was observed in Au/Co multilayered films. When Co layer thickness was 4.7 Å, the effective perpendicular anisotropy energy Ku was 9.6x106 erg/cm3. The surface (interface) anisotropy energy constants, Ks, of Au/Co and Au/Fe multilayered films were estimated to be 0.42 erg/cm2 and 0.51 erg/cm2, respectively. The volume contribution, Kv, was interpreted from the observed value of saturation magnetization and the bulk values of magnetocrystalline anisotropy energy constants K1 and K2.

We begin by reviewing earlier work involving the epitaxial growth of diluted magnetic semiconductor (DMS) layers, heterostructures and superlattices. We also describe current efforts at introducing new materials – such as Cd1-xMnxSe – to the family of MBE-grown DMS alloys. We then discuss some of the unique properties of DMS materials that make the study of thin film structures attractive, with particular emphasis on two general aspects. First, we look at the new opportunities in magnetism that are provided by epitaxially grown DMS films. Second, we examine some of the novel phenomena made possible by sp-d exchange effects in the context of DMS quantum well structures.

Epilayers of metastable zincblende MnSe and MnTe have been grown by molecular beam epitaxy. The MnSe structures have been used to study magnetic ordering in thin layers by means of optical and magnetic measurements. Preliminary optical reflectance measurements performed on samples of zincblende MnTe indicate a bandgap of approximately 3.15eV, while double barrier quantum structures demonstrate optical transitions corresponding to 2D electron and hole confinement. Optical measurements further provide insight into the band offsets existing between MnTe and CdTe, as well as between MnTe and ZnTe epilayers.