Search

We present a comparative study of the spin wave properties in two magnetic films patterned into an artificial square spin ice-like geometry. The array elements are rectangular islands with the same lateral dimensions but with different thicknesses: 10 nm and 30 nm. Using Brillouin light scattering, the frequencies of spin wave excitations were measured as a function of the magnetic field going from positive to negative saturation. We find substantial changes with thickness to spin wave mode frequencies and the number of detected modes. Frequencies of spin waves localized at element edges are observed to evolve non-monotonically with magnetic fields and soften at critical fields. These critical fields enable us to extract information of the magnetization reversal of individual islands within the array. Finally, we discuss the effects of separation between islands and examine the possibilities for dynamic coupling through the overlap of collective edge modes.

We have exploited the pseudomorphic growth of the magnetically soft Fe3Pt phase on top of L10- FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO3(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchangecoupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreases down to 21% of the hard layer value for Fe3Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO3; this maximum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%. [ABSTRACT FROM AUTHOR]

We have exploited the pseudomorphic growth of the magnetically soft Fe3Pt phase on top of L10- FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO3(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchangecoupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreases down to 21% of the hard layer value for Fe3Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO3; this maximum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%. [ABSTRACT FROM AUTHOR]

We deposited nanogranular Co/Cu multilayers made of thin fragmented Co layers separated by thicker Cu layers to study how the structure and the microstructure of magnetic nanogranular samples change as the average particle size is reduced and how these changes affect the giant magnetoresistive response of the samples. Indeed, thanks to the vertical periodicity of the structure, namely, to the fact that Co/Cu interfaces display an ordered stacking and are not randomly distributed within the samples as in conventional granular materials, their self-correlation and cross correlation can be investigated. In this way, the characteristic length scale of the Co/Cu interfacial roughness that is strictly related to the giant magnetoresistive response of the samples and the universality class of the growth mechanism that affects the systems structure can be both accessed. The Co/Cu nanogranular multilayers were characterized using different x–ray techniques, from specular reflectivity, which allows to probe the multilayer development in the vertical direction, to grazing incidence small angle diffuse scattering, which provides information on the self-correlation and cross correlation of the Co/Cu interfaces. Furthermore, diffraction measurements indicate that the degree of structural disorder increases by decreasing the thickness of the Co layers. Magnetoresistive and magnetization measurements are as well presented and discussed with the results of the structural characterization. [ABSTRACT FROM AUTHOR]

Focused ion beam was utilized to locally modify magnetism and structure of L10 FePt perpendicular thin films. As a first step, we have performed a magnetic, morphological, and structural study of completely irradiated FePt films with different Ga+ doses (1×1013 –4×1016 ions/cm2) and ion beam energy of 30 keV. For doses of 1×1014 ions/cm2 and above a complete transition from the ordered L10 to the disordered A1 phase was found to occur, resulting in a drop of magnetic anisotropy and in the consequent moment reorientation from out-of-plane to in-plane. The lowest effective dose in disordering the structure (1×1014 ions/cm2) was found not to affect the film morphology. Taking advantage of these results, continuous two-dimensional (2D) patterns of perpendicular magnetic structures (250 nm dots, 1 μm dots, 1 μm-large stripes) were produced by focused ion beam without affecting the morphology. The 2D patterns were revealed by means of magnetic force microscopy, that evidenced peculiar domain structures in the case of 1 μm dots. [ABSTRACT FROM AUTHOR]

A set of ferromagnetic thin films and multilayers containing 3d metals (Fe, Co) in different amounts was prepared by rf sputtering. Each sample exhibits a specific magnetic and magnetoresistive behavior, as expected for materials having different saturation magnetizations, magnetic anisotropies, and surface-to-volume ratios. From room temperature down to about 10 K, the magnetoresistance is explained in terms of well-known mechanisms; at low fields, a negative magnetoresistance is measured. Between ∼10 and 30 K, the zero-field electrical resistance appears to be dominated by electron-phonon scattering. At lower temperatures, where the R vs T curve is almost saturated, a sudden drop of the resistance appears, whose magnitude and position vary from sample to sample. Below the drop temperature, a region of positive magnetoresistance is systematically observed at around H=0 in measurements done with the magnetic field applied either parallel or perpendicular to the film plane. The dip magnitude increases with decreasing temperature. The anomaly appears to be related to the presence of magnetic inhomogeneity in the samples. The experimental results are not explained in terms of standard magnetoresistance mechanisms. Effects related to quantum coherence of conduction electrons may be the source of the observed anomalies. The role of weak localization of electrons, inhibited by the additional scattering provided by the magnetic inhomogeneity on the nanometer scale, is discussed. [ABSTRACT FROM AUTHOR]

This paper presents a detailed study of structure, morphology, and magnetic properties in FePt thin films epitaxially grown on MgO(100) at intermediate temperatures (≅380 °C). It focuses on the effects obtained by in situ annealing the FePt films after deposition. We have demonstrated that the annealing allows one to complete the ordering, thus obtaining an epitaxial L10-FePt film with large perpendicular anisotropy (up to 3×107 erg/cm3) and high perpendicular squareness and remanence ratio (both higher than 0.85). At the same time, we have found a peculiar morphology evolution by increasing the annealing time: the interconnected mazelike grains evolve towards interconnected dotlike grains of reduced size (down to 10 nm). Due to the interconnection at the grains basis, the increase in the film perpendicular coercivity with the annealing process is moderate (up to 4.1 kOe), leading to an increasing anisotropy/coercivity ratio with the annealing time. As a further step towards the understanding of the properties evolution with annealing, we have investigated the magnetic domain pattern and analyzed the domain-period dependence on the anisotropy constant in comparison with the behavior expected by the Kooy–Enz theory [C. Kooy and U. Enz, Philips Res. Rep. 15, 7 (1960)]. The main magnetic properties and reduced grain size obtained after the in situ annealing are promising to realize perpendicular recording media with reduced bit size, high thermal stability, and suitable switching field. [ABSTRACT FROM AUTHOR]

Magnetometric and magnetic force microscopy (MFM) measurements were performed on [Co(6 Å)/Au(27 Å)][SUB27] multilayers grown at different sputtering pressures (0.8-9 Pa). All the as-prepared samples display perpendicular magnetic anisotropy that has its maximum value at intermediate pressures, while a monotonic decrease of the saturation magnetization was found with increasing pressure. As found by MFM, a relevant characteristic of these systems is the magnetic stripe domain structure. The application of the stripe domain model of Draaisma and de Jonge [H. J. G. Draaisma and W. J. M. de Jonge, J. Appl. Phys. 62, 3318 (1987)] allows us to satisfactorily reproduce the magnetization processes and to determine the anisotropy constants (K[SUBeff]) starting from the domain width. The obtained K[SUBeff] values display the same behavior and order of magnitude as those deduced from the area enclosed between parallel and perpendicular magnetization curves. The measurement of the stripe domain size with MFM thus results in an easy and reliable method for the evaluation of the anisotropy constants in multilayers with perpendicular anisotropy. [ABSTRACT FROM AUTHOR]

The effect of the reduction of the magnetic layer thickness on sample correlated roughness in Co/Cu granular samples produced through the incomplete layer method is examined. The fragmentation process has promoted conformal nanoscale roughness and has lowered the giant magnetoresistance response of the system.

The evolution of structure, magnetic microstructure, and magnetic anisotropy in Co/Au multilayers as a function of the number of repetitions is discussed. For all the multilayers K(super eff) is positive indicating that the magnetization easy axis is perpendicular to the plane and that the tendency toward perpendicular magnetization is enhanced when the repetition number of layers is increased, in agreement with results obtained by AGFM and MFM.

We systematically investigated, both theoretically and experimentally, Zr1-xFexO2-y ranging from diluted (x≈0.05) up to large (x≈0.25) Fe concentration. By atomic layer deposition, we grew thin films of high-k zirconia in cubic phase with Fe uniformly distributed in the film, as proven by time of flight secondary ion mass spectrometry and transmission electron microscopy measurements. Iron is in Fe3+ oxidation state suggesting the formation of oxygen vacancies with y concentration close to x/2. By ab-initio simulations, we studied the phase diagram relating the stability of monoclinic vs. tetragonal phase as a function of Fe doping and film thickness: the critical thickness at which the pure zirconia is stabilized in the tetragonal phase is estimated ranging from 2 to 6 nm according to film morphology. Preliminary results by X-ray magnetic circular dichroism and alternating gradient force magnetometry are discussed in comparison to ab initio data enlightening the role of oxygen vacancies in the magnetic properties of the system. [ABSTRACT FROM AUTHOR]