CoPd Thin Films Research Articles

Chirality-Induced Noncollinear Magnetization and Asymmetric Domain-Wall Propagation in Hydrogenated CoPd Thin Films.

Array-patterned CoPd-based heterostructures are created through e-beam lithography and plasma pretreatment that induces oxidation with depth gradient in the CoPd alloy films, breaking the central symmetry of the structure. Effects on the magnetic properties of the follow-up hydrogenation of the thin film are observed via magneto-optic Kerr effect microscopy. The system exhibits a strong vertical and lateral antiferromagnetic coupling in the perpendicular component between the areas with and without plasma pretreatment, and asymmetric domain-wall propagation in the plasma-pretreated areas during magnetization reversal. These phenomena exhibit evident magnetic chirality and can be interpreted with the Ruderman-Kittel-Kasuya-Yosida coupling and the Dzyaloshinskii-Moriya interaction (DMI). The sample processing demonstrated in this study allows easy incorporation of lithography techniques that can define areas with or without DMI to create intricate magnetic patterns on the sample, which provides an avenue toward more sophisticated control of canted spin textures in future spintronic devices.

Dependence of magnetic domain patterns on plasma-induced differential oxidation of CoPd thin films

We demonstrate the evolution of the micro-patterned magnetic domains in CoPd thin films pretreated with e-beam lithography and O2 plasma. During the days-long oxidation, significantly different behaviors of the patterned magnetic domains under magnetization reversal are observed via magneto-optic Kerr effect microscopy on different days. The evolution of the magnetic behaviors indicate critical changes in the local magnetic anisotropy energies due to the Co oxides that evolve into different oxide forms, which are characterized by micro-area X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. The coercive field of the area pre-exposed to plasma can decrease to a value 10 Oe smaller than that unexposed to plasma, whereas after a longer duration of oxidation the coercive field can instead become larger in the area pre-exposed to plasma than that unexposed, leading to an opposite magnetic pattern. Various forms of oxidation can therefore provide an additional dimension for magnetic-domain engineering to the current conventional lithographies.

Magneto-optical study of anomalous magnetization reversal in the presence of anisotropy dispersion in CoPd thin films

Magneto-optical study of anomalous magnetization reversal in the presence of anisotropy dispersion in CoPd thin films

PLD growth of CoPd thin films and characterization of their magnetic properties by magneto optical Kerr effect

CoPd alloy thin films with different thicknesses and Co/Pd ratios have been deposited on Si (100) substrate by pulsed laser deposition (PLD). The magnetic properties were investigated by using the magneto-optical Kerr effect (MOKE) in both longitudinal and polar geometries. The results show that the films with thickness in the range of 6–24 nm, deposited at a low substrate temperature of 200 °C, are mostly magnetized in the plane of film. Higher deposition temperature forces the magnetic easy axis to orient in the perpendicular direction of the films.

Hydrogenation-induced reversible spin reorientation transition in Co50Pd50 alloy thin films

Abstract Because of the Pd-catalyzed hydrogen dissociation and absorption, magnetic Pd-alloys provide a model system for the investigation of the critical hydrogenation effect on magnetism. In this study, Co 50 Pd 50 (CoPd) alloy thin films were fabricated by e-beam-heated co-evaporation on Al 2 O 3 (0001) substrates. These films exhibited a thickness-dependent spin reorientation transition (SRT) from perpendicular direction to in-plane direction with increase of thickness. For 10-30 nm-thick CoPd alloy films with perpendicular magnetic anisotropy (PMA), hydrogenation triggered a SRT to an in-plane anisotropy. The reversibility of SRT was demonstrated by cyclicly changing the hydrogen gas pressure. Furthermore, hydrogenation-induced SRT randomized the magnetic domain orientation. The surface morphology of the CoPd thin films was composed of nanoclusters, which may play a crucial role in hydrogen dissociation and affect PMA. In comparison with a bare CoPd film, a stronger PMA and a less pronounced hydrogenation-induced SRT were observed in a Pd-capped CoPd film. These observations suggest that the hydrogen content in CoPd alloy films can drastically and reversibly modify PMA, inferring the possible hydrogenation-induced charge transfer and modulation of electronic structure in CoPd.

Structure and magnetization in CoPd thin films and nanocontacts

We present results showing the structural and magnetic properties of MBE-grown extended films and nanostructured elements of various CoPd alloys. X-ray diffraction studies show that the thin films are polycrystalline, yet exhibit a strong preferential growth orientation along the (111) direction. Magnetic force microscopy and SQUID are used to gain an understanding of the magnetic behavior of the CoPd system with respect to competing anisotropy contributions, based on temperature-dependent SQUID data, collected between 4 and 300K. The idea and potential implications of using CoPd as a contact material to achieve spin injection in carbon nanotube-based devices is discussed.

Magnetoelectric Effect in $L 1_{0}$-CoPd Thin Films

The effect of an applied electric field on the magnetic properties of L 10-ordered CoPd thin films is investigated by first-principle calculations. Both the magnetic moment and the magnetocrystalline anisotropy of the surface atoms are changed by the electric field, but the net effect depends on the surface termination. The magnetocrystalline anisotropy switches from in-plane to perpendicular in the presence of external electric field. Typical magnetic-moment changes are 0.1 μB per eV/A. The main mechanism is the shift of the Fermi level, but the anisotropy change also reflects a crystal-field change due to incomplete screening.

Structural and magnetic properties of FePd and CoPd alloy epitaxial thin films grown on MgO single-crystal substrates with different orientations

FePd and CoPd alloy thin films were prepared on MgO single-crystal substrates of (001) B1 , (110) B1 , and (111) B1 orientations at 600 °C by ultra high vacuum rf magnetron sputtering. L1 0-FePd(001) films with the c-axis perpendicular to the substrate surface are obtained on MgO(001) B1 substrates. FePd epitaxial films consisting of L1 0(110) and L1 0(011) crystals are formed on MgO(110) B1 substrates. The c-axis of L1 0(110) crystal is parallel to the substrate surface, whereas that of L1 0(011) crystal is 44° canted from perpendicular direction. L1 0-FePd(111) films with the c-axis 54° canted from the perpendicular direction are formed on MgO(111) B1 substrates. L1 0 ordering degree of these FePd films varies depending on the substrate orientation. On the other hand, disordered CoPd thin films of (001) A1 , (110) A1 , and (111) A1 orientations epitaxially grow on MgO substrates of (001) B1 , (110) B1 , and (111) B1 orientations, respectively. The magnetization properties of L1 0 ordered FePd and A1 disordered CoPd thin films are influenced by the crystal structure, the ordering degree, and the film orientation.

Order-disorder phase transition in CoPd thin films

The thin films of a CoPd alloy in the equiatomic composition region are prepared by condensation at different substrate temperatures. The substrate temperature is varied from the liquid nitrogen temperature to +280°C. At low substrate temperatures, the crystal structure of the condensed films is the single-crystal blocks of the hexagonal close-packed (hcp) phase. As the substrate temperature is further increased, the domains characterized in the initial state by the microdiffraction patterns in the form of a diffuse halo appear in the films, and these domains have a clear-cut boundary with the regions indicated by point reflections in the electron diffraction patterns. At substrate temperatures from +150 to 160°C, the CoPd alloy films in the equiatomic composition region are fully amorphous. The given state is a polymorphic transformation of the martensitic type. It arises in the martensitic transformation of the low-temperature hcp phase to the high-temperature fcc phase.

Electrodeposition of Magnetic CoPd Thin Films. Influence of Plating Condition

Electrodeposition of magnetic CoPd thin films from a chloride bath containing glycine was investigated. The effect of applied current density (CD), bath composition, solution pH on film composition and current efficiency (CE) are discussed. Alloy composition, is dependent on bath composition and not on the pH of the solution. CEs are higher when the CD is between 25 and 50 mA cm-2. XRD data show that CoPd alloys are amorphous. For CD greater than or equal to 50 mA cm-2 the films show a typical cauliflower morphology whereas a smooth surface film is obtained for CD < 50 mA cm-2. Cracks and holes are observed with low CDs, with increasing solution pH. Magnetic measurements show that the films are easily magnetized when the applied field is longitudinal. Magnetic saturation (Ms) is dependent on the alloy composition. Coercivities were obtained in the range of 84 - 555 Oe were not attributed to any plating variable.

Full micromagnetics of recording on patterned media

Numerical micromagnetics of the bit writing process revealed the theoretical limits for remanence, coercive field, switching behaviour at a short time scale of less than 1 ns for patterned recording media. We discuss our recent results concerning the influence of the granular microstructure on the fast switching processes of typical CoCrPtX, FePt and CoPd thin films used for high density magnetic recording with longitudinal and perpendicular anisotropy. In detail, we will show that the degree of the exchange coupling between neighbouring grains, the grain size and its distribution and the offset between recording head and bit structure finally control the magnetization reversal properties of the individual bits.

Coercivity and microstructure in Co-Pt and Co-Pd thin films

Thin films of Co-Pt and Co-Pd have been electrodeposited from alkaline baths based on cobalt amino-citrate complexes and amino-nitrite complexes of the noble metal, on copper substrates coated with Ni-P ACD (10 μm). Co-Pd films can be obtained in a wide range of compositions; both fcc and hcp structures can be present (the last one only for Pd ≤ 16 at%); the lattice constant varies continously with varying composition. The Bragg diffraction peaks are broadened, suggesting a poorly defined crystalline structure or a high density of defects. The grains appear to be homogeneous and regular, their size being generally below 100 nm. Co-Pt films are rich in cobalt; they show a fcc structure with a lattice constant varying discontinously and with a (111) PO. A well defined crystalline structure is obtained, with fine and regular crystallites (size below 100 nm), and sharp Bragg peaks. Differences in microstructure can be related to large differences in magnetic properties. While Co-Pt films show high coercivities (up to 200 kA/m) and high squareness, Co-Pd films, in the whole range of compositions investigated, show very low coercivities and varying squareness. In the Co-Pd system, hysteresis cycles sometimes suggest the presence of two phases with different micromagnetic behaviours and different coercivities; only one of the phases gives the observed value of coercivity. We further investigated the effect of layering through pulsed current deposition; the growth of the different phases could be controlled through control of deposition parameters in the electrodeposition process. Co-Pd films could be promising candidates for thin-film heads in magnetic recording media; their possibilities have not yet been fully assessed, but their magnetic properties, together with their possible high corrosion resistance and good mechanical properties, deserve further studies.

On magnetic anisotropy in sputtered Co-Pd alloy films

This work presents the magnetic and electric investigation of Co-Pd thin films. It has been found that Co-Pd films obtained by the cosputtering method exhibit uniaxial anisotropy with the easy axis parallel to the plane of the film. The internal stress measurements showed the existence of the compressive stresses anisotropic in character.