Tailoring Magnetic and Transport Anisotropies in Co100−x–Cux Thin Films through Obliquely Grown Nano-Sheets (original) (raw)
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Thin films of Co-rich transition metal or metal CoeMT (MT ¼ V, Cr, Cu, Zn, Cd, Hf) compounds were fabricated as a superposition of oblique nano-sheets (z300 x 80 Â 5 nm for each nano-sheet) from a mixture of Co and MT plasmas. Because the X-ray diffraction patterns of all of the films showed a similar nano-crystalline microstructure, the oblique nano-sheets were visualized by high-resolution transmission electron microscopy. This nano-morphology generated strong in-plane uniaxial magnetic anisotropy, UMA, as we explained in this work, for all the as-deposited films. The evolution of this magnetic anisotropy was studied at temperatures up to 450 C. Three different cases were observed after these heat treatments depending on the MT component of the film: (1) UMA was lost for temperatures z 400 C, (2) UMA retained the same value until the highest temperature was reached, or (3) UMA was enhanced by a factor greater than 2 for the highest temperature. This behavior can be explained by considering of the various processes of structural relaxation and crystallization produced by heat treatment and affected by the nano-sheet morphology.
Manipulation of magnetic anisotropy of Co ultrathin films by substrate engineering
Journal of Applied Physics, 2011
The magnetic and structural properties of Co films prepared on various substrates were investigated in situ based on the surface-magneto-optical Kerr effect (SMOKE) and using reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). The magnetic signals of the Co films were found to change significantly depending on the underlying substrates, the film thickness, and the temperature. Both STM and RHEED observations revealed that the shape and atomic structure of the Co islands were very different, which explains the observed magnetic anisotropy in SMOKE. We also observed a steep increase in coercivity for Co films thicker than 1.5 bi-layers grown on an Ag(111) film. This increase may be interpreted as a fcc-to-hcp structural transformation. V
Films produced by means of ultrashort pulsed laser deposition (uPLD) and constituted of Co nanoparticles (NPs) mixed with Cu ones exhibit peculiar morphological and topological properties. In particular, the NPs obtained by uPLD retain their individuality with a moderate coalescence which permits interparticle discontinuities. Due to this condition, the NP interface contributes significantly to the electron transport mechanisms depending on the magnetizing field. As a consequence, magnetoresistance effects are evidenced which do not saturate up to external magnetizing fields much higher than the value required for the saturation of the macroscopic magnetization. Moreover, when the cobalt volume fraction (x) is lower than 35%, the set of magnetic, resistive and magnetoresistive data shows that the magnetic percolation among the Co particles is not completely obtained and a transport mechanism of the giant magnetoresistance (GMR) kind is active in the uPLD films, notwithstanding the fact that the average particle size is higher in comparison with that expected for GMR optimization. On the other hand, if the contact among Co particles is obtained (x 50%) the anisotropic magnetoresistance (AMR) becomes the prominent effect. In this circumstance, the presence of interparticle discontinuities is still deducible by the experimental evidence of a negative derivative of the magnetoresistance ratio versus the applied magnetic field. In the same x range (x 50%), the AMR increases with the Co content, while zero field resistivity does not change.
Magnetic anisotropy modification in ultrathin Co(0001) film epitaxially grown on Mo(110)
Journal of Magnetism and Magnetic Materials, 2005
Modification of anisotropy has been studied in Mo(1 1 0)/Co(0 0 0 1)/Au structures grown by molecular beam epitaxy on a monocrystalline ð1 12 0Þ sapphire substrate. In order to fit the experimental data, the out-of-plane anisotropy energy contribution as well as that of the uniaxial in-plane were considered. Magnetic anisotropy constants as a dependence on Co thickness were determined in the range of spin-reorientation phase transition. Observed magnetic anisotropy can be explained by the presence of strains in Co film induced by the Mo(1 1 0) buffer.
Magnetic Anisotropy of Co Films Annealed by Laser Pulses
Solid State Phenomena, 2008
The magnetic properties of an ultrathin cobalt film were modified by a focused femtosecond pulsed laser beam. The Co wedge, with a thickness ranging from 0 to 2 nm, sandwiched by Au films was prepared using ultra-high vacuum magnetron sputtering on a mica substrate. The modifications of the laser induced magnetic anisotropy were investigated using magneto-optic Kerr microscopy and MFM/AFM techniques. The laser induces: (i) local reorientation of magnetization from an in-plane to a perpendicular state and (ii) an increase of the coercivity field. A corresponding increase of the perpendicular magnetic anisotropy is discussed considering an improvement of the Co/Au interfaces.
Tunable magnetic anisotropy of ultrathin Co layers
Applied Physics Letters, 2005
We prepared multilayers, consisting of an epitaxial Au/ Co/ Au/ Cu͑111͒ architecture on Si͑111͒ substrates, to understand the magnetic anisotropy of an ultrathin Co layer in relation to its structure. The room-temperature magnetization of an 8-monolayer ͑ML͒-thick Co layer is predominately either in-plane or out-of-plane depending upon the thickness of the Au underlayer. Specifically, for a Co film grown on a 2-ML-thick Au, the Co film has a distorted fcc structure and in-plane magnetic anisotropy. For a Co film grown on a 6-ML-thick Au, the Co film has a distorted hcp structure and out-of-plane magnetic anisotropy.
Influence of film morphology on perpendicular magnetic anisotropy
Physical Review B, 2001
Perpendicular magnetic anisotropy ͑PMA͒ appears in epitaxial films mainly due to the broken symmetry at the interface. As a result, ultrathin magnetic layers tend to be perpendicularly magnetized. With increasing film thickness, the shape anisotropy overcomes this interface contribution and forces the sample magnetization into the surface plane. We show that previous experimental studies of the magnetic anisotropy energies in the Co/Cu͑111͒ system are affected by the large roughness of the Co films, resulting in underestimated values for the Co-Cu interface anisotropy. By using a surfactant ͑Pb͒ to assist the growth of Co layers we are able to prepare Co films and Cu/Co bilayers of homogeneous thickness and negligible roughness, and to determine a more accurate value for the Co-Cu interface anisotropy. With the aid of a simple model calculation, we demonstrate that roughness will substantially affect experimentally determined values of PMA.
The magnetic and microstructural properties of Co-Cr thin films with perpendicular anisotropy
Journal of Magnetism and Magnetic Materials, 1983
This paper reports measurements of the magnetic properties of dc sputter deposited Col00_xCr x alloy thin films for 0 < x ¢ 30 ate. Properties of interest are those obtained from the in-plane and perpendicular hysteresis loops such as magnetization, saturation fields and coercivities. These properties are correlated with the microstructure, crystal structure and, to some extent, the magnetic domain structure of the films. For particular preparation conditions and within a certain composition range the films are found to have some of the properties suitable for perpendicular magnetic recording appfications, i.e., perpendicular magnetization and high coercivity.
Manipulating magnetic anisotropies of Co MgO(001) ultrathin films via oblique deposition
We present a systematic investigation of magnetic anisotropy induced by oblique deposition of Co thin films on MgO (001) substrates by molecular beam epitaxy at different deposition angles, i.e., 0 • , 30 • , 45 • , 60 • , and 75 • with respect to the surface normal. Low energy electron diffraction (LEED), surface magneto-optical Kerr effect (SMOKE), and anisotropic magnetoresistance (AMR) setups were employed to investigate the magnetic properties of cobalt films. The values of in-plane uniaxial magnetic anisotropy (UMA) constant K u and four-fold magnetocrystalline anisotropy constant K 1 were derived from magnetic torque curves on the base of AMR results. It was found that the value of K u increases with increasing deposition angle with respect to the surface normal, while the value of K 1 remains almost constant for all the samples. Furthermore, by using MOKE results, the K u values of the films deposited obliquely were also derived from the magnetization curves along hard axis. The results of AMR method were then compared with that of hard axis fitting method (coherent rotation) and found that both methods have almost identical values of UMA constant for each sample.