Magnetic Thin Film Structures Research Articles

Thermal stability of thin Ti films on Al single crystal surfaces

Chemical roughness and alloy formation at metallic interfaces can significantly degrade the performance of multilayer thin film magnetic device structures. We have investigated the use of Ti interlayers, one or two atoms thick, to stabilize the interface for ordered growth of Fe films on Al(100), a system characterized by considerable interdiffusion at room temperature. The practicality of the interlayer concept is strongly coupled to the stability of the interlayer at elevated temperatures. In this investigation we have characterized the structure of thin Ti layers on Al single crystal surfaces as a function of temperature using Rutherford backscattering and channeling and low-energy ion scattering. The Ti layers are shown to be stable up to temperatures of about 675 K, at which point diffusion of Ti into the Al lattice occurs. Channeling measurements show that the Ti atoms sit on Al lattice sites as substitutional impurities. The stability of the Ti film appears to increase with the packing density of the Al surface, being slightly more stable for the close-packed Al(111) surface, and diffusing into the more open Al(110) surface at a lower temperature.

Measuring lateral magnetic structures in thin films using time-of-flight polarized neutron reflectometry

Polarized neutron reflectometry (PNR) has recently been applied to study lateral magnetic structures such as regular micron-sized magnetic arrays on a surface. To date, however, there is a lack of detailed accounts of the features observed in the scattered intensity map in the special case of time-of-flight (TOF) PNR. We present here preliminary measurement results on lithographically produced arrays of micron-sized rectangular permalloy magnetic bars. The measurements demonstrate the potential of the method to provide detailed structural information on a laterally patterned sample, as well as on its magnetic characteristics. The information can be obtained by analyzing the specular reflection along with three off-specular Bragg sheets. Most of the features seen experimentally can be interpreted by using simple heuristic arguments. In addition, we also present results of a study of lateral magnetic domains in an exchange-biased Co/CoO bilayer film to illustrate the capability of TOF PNR in the study of large lateral magnetic domains in the case when almost no off-specular scattering is detected.

Polarized neutron grazing incidence diffraction on magnetic epitaxial thin films

In order to study the in-plane crystallographic structure of magnetic thin films, we have developed a neutron grazing incidence diffraction (GID) set-up that has been mounted on the EROS reflectometer at the LLB. This set-up allows us to observe the diffraction peaks in the plane of epitaxial thin films. As an example, we present polarized GID measurements on an epitaxial ferromagnetic thin film of the perovskite oxide La 0.7Sr 0.3MnO 3(0 0 1) deposited on SrTiO 3(0 0 1) (of a surface 1 cm 2). This is the first report on polarized GID measurements on a very thin magnetic film (20 nm).

Applications of photoemission electron microscopy (PEEM) in magnetism research

This paper reviews the application of X-ray photoemission electron microscopy (X-PEEM) to problems in modern magnetism. In particular, the ability to determine the magnetic domain structure of antiferromagnetic thin films will be discussed.

Magnetic Domain Structure of MnAs Thin Films as a Function of Temperature

We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a magnetic force microscope. Weobserved, by an atomic force microscope, rectangular defects along GaAs [110] direction which disperse randomly on the surface of MnAs/GaAs (001). The Curie temperature of MnAs is 45 C, and it is successfully confirmed directly by the variable temperature magnetic forcemicroscope observation. We also investigated magnetic domain structures of MnAs/GaAs (111)B, and no apparent relation was observedbetween the topographic structure and the magnetic domain structure.(Received July 16, 2003; Accepted September 25, 2003)Keywords: MnAs, magnetic force microscopy, phase transition

Soft X-ray magnetic scattering as a probe of recording media

We highlight recent experiments that use magnetic X-ray scattering as a probe of magnetic recording media. Resonant small-angle scattering at the 2p levels of 3d transition elements strongly enhances scattering from both magnetic and chemical structure of thin films and allows a quantitative determination of the chemical and magnetic grain sizes with nm resolution. The chemical grain size measurements compliments the information determined by transmission electron microscope. However, the ability to measure magnetic correlations in the <100 Å range is well below the resolution that is currently achievable in most magnetic imaging techniques. Information about length scales in non-magnetic underlayers is also provided by these sensitive scattering measurements by tuning the photon energy to elements that are specific to the underlayer structure. These techniques should continue to provide insight and feedback into the development of future recording media.

Imaging the magnetic spin structure of exchange-coupled thin films.

We have investigated the magnetic spin structure of a soft-magnetic film that is exchange-coupled to a hard-magnetic layer to form an exchange-spring layer system. The depth dependence of the magnetization direction was determined by nuclear resonant scattering of synchrotron radiation from ultrathin 57Fe probe layers. In an external field a magnetic spiral structure forms that can be described within a one-dimensional micromagnetical model. The experimental method allows one to image vertical spin structures in stratified media with unprecedented accuracy.

Planar Hall effect in thin-film magnetic structures. Cobalt films on silicon substrates

Field and angular dependencies are investigated for the planar Hall effect in ferromagnetic cobalt films on silicon substrates. An angular period doubling is observed with crossover from high magnetic fields to low ones. In intermediate magnetic fields, the angular dependence symmetry with respect to abscissa axis breaks down and a hysteresis behavior reveals both in field and angular dependencies. Comparison between theory and experiment makes it possible to determine the easy axis direction and the anisotropy field.

Recent developments in synchrotron Mössbauer reflectometry

Synchrotron Mossbauer Reflectometry (SMR), the grazing incidence nuclear resonant scattering of synchrotron radiation, can be applied to perform depth-selective phase analysis and to determine the isotopic and magnetic structure of thin films and multilayers. Principles and methodological aspects of SMR are briefly reviewed. Off-specular SMR provides information from the lateral structure of multilayers. In anti-ferromagneticly coupled systems the size of magnetic domains can be measured.

Magnetic Domain Structures in CoNiFe Thin Films and Lines

ABSTRACTThin films and arrays of lines of magnetic CoNiFe alloy have been produced by electrodeposition. A magnetic field was applied during the electrodeposition process in order to induce a magnetic anisotropy in the sample. The dependence of the magnetic properties and the magnetic domain structures on the thickness of the films is reported. In addition to this, the magnetic properties and the domain structure of a thin film and an array of lines, with the same thickness and deposited in the same conditions, have been compared. An increase in the coercivity of the array of lines has been shown.

Honeycomb domain structures in amorphous TbFe thin films

The magnetic properties and domain structure of amorphous TbFe thin films were studied by magnetic measurement and magnetic force microscope. Honeycomb domain structures were found in the as-deposited amorphous film. The domain structures were composed of many small white round dots embedded in the black matrix, which formed an irregular hexagonal pattern with some deformation. The average dot size was about 450 nm, with an average separation of 610 nm. The derived domain wall energy density γ and the exchange constant A were 0.95×10−2 and 1.79×10−11 J/m, respectively.

The spin-valve transistor: Fabrication, characterization, and physics (invited)

An overview is given of the fabrication, basic properties, and physics of the spin-valve transistor. We describe the layout of this three-terminal ferromagnet/semiconductor hybrid device, as well as the operating principle. Fabrication technologies are discussed, including vacuum metal bonding. We characterize properties of the device relevant for possible applications in magneto-electronics, such as relative magnetic response, output current, and noise behavior. Furthermore, we illustrate the unique possibilities of the spin-valve transistor for fundamental studies of the physics of hot-electron spin transport in magnetic thin film structures.

Polarized neutron reflectometry: recent developments and perspectives

Polarized neutron reflectometry (PNR) has an important role in solving non-collinear magnetic structures in thin films. In principle PNR provides the unambiguous determination of multi-axial magnetic depth profiles in systems of scientific and technological importance. However, only a limited number of problems have been solved unimpeachably, because the magnetic depth profiles were obtained by fitting procedures yielding solutions whose main features were not evident in the raw data. A recent formulation of reflectometry, and the concurrent development of “total polarimetry” are now stimulating the design of neutron polarization and polarization analysis geometries capable of determining directly if and how a magnetic system contains a non-collinear structure in the film ( x– y) plane. In the simplest of these geometries the neutrons are polarized and analyzed along the z-axis perpendicular to the film plane.

Magnetic Properties and Structure of (Co100-xFex)50Pt50 Alloy Thin Films.

The magnetic properties of (Co100-xFex)50Pt50 (0 ≤ x ≤ 100) alloy thin films in conjunction with the structure are studied. The intrinsic perpendicular magnetic anisotropy constant Ku measured at room temperature increases with order parameter S and decreases with tetragonality c/a. This result is at variance with a calculation based on first-principle analysis at the order parameter S=1. Ku increases with S for all compositions. The estimated Ku values obtained by extrapolation to S=1 for (Co100-xFex)50Pt50 would be nearly the same for x from 0 to 56, but increases with x for x larger than 56. The present result is consistent with the theoretical one, provided that the temperature dependence of Ku is neglected.

Spatially modulated magnetic structures in thin films

The axial next-nearest neighbour Ising (ANNNI) model is studied for thin films of up to $L= 10$ layers, with a distinct phase diagram for each film thickness. The systematics of the ordered phases, as obtained from mean-field theory, Monte Carlo simulations, and low temperature expansions, is discussed. Results are compared to those for the ANNNI model in the limit $L \longrightarrow \infty$.

Electronic and magnetic structures in metallic thin films

Electronic and magnetic structures in metallic thin films

Structure of magnetic thin films and nanostructures studied by extended X-ray absorption fine structure

Thin magnetic films deposited on single-crystal substrates have been the subject of numerous studies during the last decade. Their bidimensional character, together with the occurrence of singular crystallographic structures, often confer to these thin films electronic properties that cannot be found in bulk solids. For example, thin nickel layers deposited on Cu(001) are found to present a perpendicular magnetic anisotropy in a very wide thickness range. We show that this can be explained by a distorted structure of nickel, originating from the strain induced by the epitaxy on the copper substrate. In this field of two-dimensional magnetism, nanostructures with a reduced lateral dimension are also investigated. Thin iron layers on MgO(001) were cut into stripes by the ‘atomic saw’ method: a compression of the substrate induces a dislocation slipping which saws both the substrate and the iron film into regular and separated ribbons. The easy magnetisation axis observed perpendicular to the stripes can be explained by a structural relaxation occurring during the structuring process. From these two studies, we see that the structure of films can be described as an elastic deformation of the bulk structure.

Analysis of ferromagnetic removable hard disc media ageing by time of flight-energy elastic recoil detection analysis

Time of flight-energy elastic recoil detection analysis (ToF-E ERDA) has been applied to study the ageing of commercial thin film hard discs. Samples from a standard commercial removable hard disc were subjected to accelerated ageing heat treatment in normal humidity from 90°C up to 240°C in steps of 30°C for 3 h each. A test using a high humidity environment at 90°C up to 40 h was also performed. The ToF-E ERDA was carried out using a 60 MeV 127I 11+ ion beam incident at 67.5° to the surface normal, and detecting recoils at 45° to the ion beam direction by measuring their time of flight and energy in a detector telescope. The magnetic thin film structure was assigned to be a CN x /Co/N–Cr/Ni–P multilayer. At temperatures higher than 180°C the CN x coating layer detoriated with an increase of surface oxygen and an N content reduction in the N–Cr layer.

The magnetic and magnetooptical properties of Fe/Ti, Zr, Pt and Fe/Ti, Zr, Pt/Fe thin-film magnetic structures

The results of investigation of the magnetic and magnetooptical properties of two-layer Fe/Ti, Zr, Pt and three-layer Fe/Ti, Zr, Pt/Fe thin-film magnetic structures are presented. The nonmagnetic layer exhibits a strong effect on the magnetic properties of samples. The magnitude of the saturation field of three-layer magnetic structures oscillates as a function of thickness of the nonmagnetic layer; the period of this oscillation depends on the thickness of the Fe layer. The Pt layer strongly affects the spectral dependences of the equatorial Kerr effect in the structures investigated.

Synchrotron Mössbauer reflectometry

Grazing incidence nuclear resonant scattering of synchrotron radiation can be applied to perform depth-selective phase analysis and to determine the isotopic and magnetic structure of thin films and multilayers. Principles and recent experiments of this new kind of reflectometry are briefly reviewed. Methodological aspects are discussed. Model calculations demonstrate how the orientations of the sublattice magnetisation in ferro- and antiferromagnetic multilayers affect time-integral and time-differential spectra. Experimental examples show the efficiency of the method in investigating finite-stacking, in-plane and out-of-plane anisotropy and spin-flop effects in magnetic multilayers.