Manganese (Mn) grows in a metastable expanded (c/a > 1) face-centered-tetragonal (fct) phase on thin fct-Co(001) template films. A layer-by-layer growth mode is observed for small Mn thicknesses. Antiferromagnetism (AFM) of fct-Mn is evidenced by the observation of shifted magnetization loops antiparallel to the cooling field direction (negative bias) and enhanced coercive fields for Co/Mn bilayers. At low temperature, magnetic exchange interactions are detected at the Co/Mn interface for nominal Mn thicknesses as low as 1.4 monolayer (ML), indicating the onset of AFM in 2-ML-thick Mn islands. However, between 2- and 5-ML Mn, a positive bias of the magnetization loops is observed in a certain temperature range below the blocking temperature (TB) of the films. This peculiar behavior is explained by the dependence of TB on both the local Mn ML thickness and the Mn island size, leading to a unidirectional coercivity enhancement in a temperature range where both blocked and unblocked regions coexist in the Mn layers.

We introduce an interface selective structure, composed of a spin-valve on top of which a thick nonmagnetic back layer is deposited as a straightforward experimental tool to measure the GMR induced by ultrathin magnetic layers. The interface selectivity of spin-dependent scattering is evidenced by calculations and illustrated in both Co/Cu/Co and Ni80Fe20/Cu/Ni80Fe20 spin-valves by an almost discontinuous behavior in the GMR ratio. The temperture dependence of the extremely short length scale associated with this discontinuity is discussed in relation to the structure of ultrathin ferromagnetic layers.

Spinel Fe3O4 contains two sites for iron: tetrahedrally coordinated sites containing Fe3+ ions and octahedrally coordinated sites containing a mixture of Fe2+ and Fe3+ ions. Scanning tunneling microscopy performed on the (001) surface of Fe3O4, grown epitaxially on MgO, shows localized charge density at the tetrahedral sites. The images show that the p(1×1) surface reconstruction (also observed during molecular beam epitaxy of Fe3O4) is produced by a displacement of the two tetrahedrally coordinated Fe ions on the unit cell surface from their bulk positions toward each other. The octahedral Fe ions are imaged as extended rows of charge density, with no resolution of atom-size features along the rows. This slight corrugation of electron charge density along the octahedral sites is consistent with the original conjectures explaining the high electrical conductivity in bulk Fe3O4: electrons move by hopping between the Fe3+ and Fe2+ atoms along the octahedral rows of Fe ions.

We present magnetoresistance (MR) data of high-vacuum magnetron sputtered NiFe/Cu multilayers (NiFe=Ni80Fe20) grown on Si(100) substrates with a Cu buffer layer and compare these with earlier results on Co/Cu(100) multilayers [1]. Measured MR values are directly proportional to the antiferromagnetically coupled fraction in the multilayers. Extrapolating to full antiparallel alignment, we can make a reliable comparison of the MR with the magnetoresistance model of Levy, Zhang, and Fert [2,3]. For the NiFe/Cu multilayers the deduced spin-asymmetry parameters are for interface and bulk scattering, respectively. Although much smaller than in our Co/Cu multilayers, , it is still the spin dependence of the interface scattering that is the main cause for the large MR values.

Coherent epitaxial Fe3O4 layers in the range of 0 to 400 Å have been grown by molecular beam epitaxy on single crystal MgO(100) substrates. The magnetic properties were studied by local magneto-optical Kerr effect experiments on a wedge shaped Fe3O4 layer, by ferromagnetic resonance and SQUID. The results show that the magnetic behavior of the Fe3O4 thin films resembles bulk Fe3O4 in the investigated thickness range.

We have studied the effect of an artificially intermixed region grown at the interfaces of Co/Cu spin valves with uncoupled layers. Two different structures are used: exchange-biased spin valves and engineered spin valves in which two layers are antiferromagnetically coupled and a third layer, on top of this system, is not coupled to the other two. It is shown that structural effects, induced by variation of the deposition parameters and by the intermixing can play an important role. Since the present study uses sputtered layers an intrinsic initial intermixing of 4-5Å is already present. For both types of spin valves Gp, ΔG and ΔR/R all show a gradual decrease when the nominal thickness of the total intermixed region is enlarged from 0 to 36Å. Also when the initial degree of intermixing is decreased by sputtering at higher Arpressure, Gp, ΔG and ΔR/R still show a gradual decrease as a function of intermixed layer thickness. Combined with the fact that there is no difference between an intermixed region of thickness t at one Co/Cu interface or intermixed regions of thickness t/2 at two interfaces, this indicates that the electron scattering in the intermixed region is predominantly spin independent, although this region preserves a magnetic moment.

We investigated the magnetization behavior of [(Co/Pd) 4-Ru]x samples with perpendicular anisotropy and a limited number of repetitions (x = 1,‥,22). In these systems the Co/Pd Multilayers behave as single magnetic entities. A detailed analysis and comparison of the magnetization curves observed by MOKE and VSM permits us to observe the magnetization reversal and hysteresis of the individual layers and to determine the antiferromagnetic coupling J between each pair of layers. A gradual increase in J is observed in all samples when going from the bottom layer to the top layer. Magnetoresistance curves show the same sharp transitions as the magnetization curves. A clear distinction can be made between an outer layer and an inner layer. These results will be compared with model calculations.

We present a theoretical study of the combined effect of spin valve and anisotropie magnetoresistance in NiFe/Cu/NiFe layered thin films, using an extended form of the semiclassical Camley and Barnás Model for electron transport. The anisotropie magnetoresistance is treated by introducing spin-dependent anisotropie mean free paths in the NiFe layers. From calculations of both magnetoresistance effects as a function of NiFe and Cu thickness, we discuss the validity of a description of the combined effect in terms of a simple summation of spin valve and anisotropie Magnetoresistance.

It is shown that a (biaxial) vibrating sample magnetometer (VSM) can be used to determine the magnetic anisotropy of thin films. Besides the commonly measured component along the magnetic field also the component perpendicular to the magnetic field was measured. Experiments were performed in a magnetic field of fixed magnitude as a function of the angle between the field and the film plane. These type of measurements give both an accurate estimate of the magnetic anisotropy and also show when domains are formed during rotation of the magnetization. The method has been applied to determine the magnetic anisotropy of Co/Pd and Co/Cu multilayers. The results are compared to those obtained with alternative methods.

The high field magnetization for Fe based Diluted Magnetic Semiconductors has been calculated. It is shown that the low temperature magnetization displays characteristic steps, related to the nearest neighbour exchange interaction JNN, provided that JNN exceeds a critical value.