Exchange through nonmagnetic insulating matrix

Exchange interactions between hard-magnetic particles in a nonmagnetic matrix are investigated by model calculations. A Landau–Ginzburg approach is developed to describe the net exchange interactions between spheres of arbitrary diameters. Introducing cylindrical coordinates and integrating over the surfaces of the adjacent spheres yields an exchange coupling which decreases with a decay length depending on interatomic exchange, intra-atomic exchange, and temperature. Typically, the decay length does not exceed a few interatomic distances. The decay is exponential but also contains a prefactor depending on the surface curvature of the grains. It increases with decreasing curvature, but this dependence is only a small correction to the leading exponential term

Boundary conditions and Berry phase in magnetic nanostructures

The effect of micromagnetic boundary conditions on the Berry curvature and topological Hall effect in granular nanostructures is investi- gated by model calculations. Both free surfaces and grain boundaries between interacting particles or grains affect the spin structure. The Dzyaloshinskii-Moriya interactions yield corrections to the Erdmann-Weierstrass boundary conditions, but the Berry curvature remains an exclusive functional of the local spin structure, which greatly simplifies the treatment of nanostructures. An explicit example is a model nanostructure with cylindrical symmetry whose spin structure is described by Bessel function and which yields a mean-field-type Hall-effect contribution that can be related to magnetic-force-microscopy images

Structure and magnetic properties of nanostructured Dy/transition-metal multilayered films

We report the results of magnetic and microstructural studies for T/Dy (T=Fe, Co, Ni) compositionally modulated films prepared in a multiple-gun sputtering system. The perpendicular anisotropy and magnetization were measured systematically for X-Å Fe/Y-Å Dy and X-Å Co/Y-Å Dy films. The layer-thickness dependence of the magnetization for Co/Dy and Fe/Dy was interpreted in terms of the antiparallel coupling between transition-metal and Dy magnetic moments. For Co/Dy films the ranges of X and Y required for perpendicular anisotropy were determined. A comparision of the structural and magnetic properties of Ni/Dy, Co/Dy, and Fe/Dy is given and the origin of the perpendicular anisotropy is discussed. Journal of Applied Physics is copyrighted by The American Institute of Physics

Magnetism of Ta Dichalcogenide Monolayers Tuned by Strain and Hydrogenation

The effects of strain and hydrogenation on the electronic and magnetic properties of monolayers of Ta based dichalcogenides (TaX2; X = S, Se, Te) are investigated using density-functional theo-ry. We predict a complex scenario of strain-dependent magnetic phase transitions involving par-amagnetic, ferromagnetic, and modulated antiferromagnetic states. Covering one of the two chalcogenide surfaces with hydrogen switches the antiferromagnetic/nonmagnetic TaX2 mono-layers to a semiconductor. Our research opens new pathways towards the manipulation of mag-netic properties for future optoelectronics and spintronics applications.Comment: 13 pages, 5 figure

Magnetic and structural properties of CoCrTa films and multilayers with Cr

We report our studies of epitaxial growth of CoCrTa films on Cr underlayers and the properties of CoCrTa/Cr multilayers. The coercivity, Hc, strongly depends on Ta composition, sputtering conditions, and the thicknesses of the magnetic layer and Cr underlayer. An Hcvalue of 1300 Oe was obtained for a Ta composition of 2 at. %, a Cr underlayer thickness of 4000 Å, and a magnetic layer thickness of 400 Å. The x-ray data show that the high Hc occurs when crystallites of the Cr underlayer and CoCrTa layer are aligned with the Cr (200) and CoCrTa (110) planes in the film plane. Thus, the c axis of the CoCrTa lies essentially in the plane of the film. When the thickness of the magnetic layer increases above 1000 Å the c axis begins to tip out of the film plane. The basal plane lattice parameter varies roughly linearly with Ta content up to 13 at. %. For the CoCrTa/Cr multilayered films, Hc values up to 1200 Oe were obtained although the c-axis orientation of the magnetic layer becomes somewhat dispersed. Models for the dependence of magnetization reversal on microstructure are discussed. Journal of Applied Physics is copyrighted by The American Institute of Physics. Magnetic and structural properties of CoCrTa films and multilayers with Cr

Magnetic properties, anisotropy, and microstructure of sputtered rare-earth iron multilayers

A study of compositionally modulated magnetic films of the form Fe/RE, particularly for RE=Nd and Dy, has been performed by vibrating sample magnetometry, ac susceptibility and x-ray diffraction. The relationship between the magnetic properties and the layer thickness was studied systematically for X-Å Fe/Y-Å Dy, as the layer thicknesses X and Y were varied from 1.8 to 20 Å. The ranges of layer thicknesses required for perpendicular anisotropy were determined. The interface and volume anisotropy energies were estimated for X-Å Fe/Y-Å Nd and the differences in the magnetic properties between X-Å Fe/7-Å Dy and X-Å Fe/7-Å Nd are discussed. Journal of Applied Physics is copyrighted by The American Institute of Physics

Highly oriented nonepitaxially grown \u3ci\u3eL\u3c/i\u3e1\u3csub\u3e0\u3c/sub\u3e FePt films

A method of preparing nonepitaxially grown, highly textured L10 FePt thin films is described. A nearly perfect (001) texture was obtained by direct deposition of FePt films on Corning 7059 glass substrates and subsequent rapid thermal annealing. The ordering and orientation of the L10-phase FePt grains were controlled by the initial as-deposited film structure, and also by the annealing process. Magnetic measurements reveal large perpendicular anisotropy for these (001) textured films. The substrates and processes used for nonepitaxial growth of L10 ordered FePt films are much more compatible with practical applications than those grown epitaxially

Structural and magnetic properties of Pr-alloyed MnBi nanostructures

The structural and magnetic properties of Pr-alloyed MnBi (short MnBi-Pr) nanostructures with a range of Pr concentrations have been investigated. The nanostructures include thin films having Pr concentrations 0, 2, 3, 5 and 9 atomic percent and melt-spun ribbons having Pr concentrations 0, 2, 4 and 6 percent respectively. Addition of Pr into the MnBi lattice has produced a significant change in the magnetic properties of these nanostructures including an increase in coercivity and structural phase transition temperature, and a decrease in saturation magnetization and anisotropy energy. The highest value of coercivity measured in the films is 23 kOe and in the ribbons is 5.6 kOe. The observed magnetic properties are explained as the consequences of competing ferromagnetic and antiferromagnetic interactions