CoPt Films Research Articles

Effect of Ag Underlayer on Microstructures and Perpendicular Magnetic Properties of CoPt Nanocomposite Thin Films

CoPt/Ag films were prepared by magnetron sputtering on glass substrates and subsequent annealing. The dependence of degree of ordering and magnetic properties on Ag film thickness and annealing conditions were investigated. It was found that the Ag underlayer played a dominant role in inducing the (001) texture of the CoPt film after annealing. CoPt films with a thickness about 20 nm and Ag underlayers with a thickness about 70 nm are easy to obtain a large degree of ordering and a perpendicular magnetic anisotropy after annealing at 700 degrees C for 30 min. CoPt/Ag films with out-of-plane coercivity (Hc (perpendicular)) in the range of 13.5-14.0 kOe and a out-of-plane squareness (S(perpendicular)) of 0.97 were obtained after annealing at 700 degrees C for 30 min. Ag underlayer is beneficial to enhance the Hc(perpendicular)and S(perpendicular) of CoPt film significantly. The degree of ordering and perpendicular magnetic properties of the CoPt films which deposited on Ag underlayer are larger than those of the single layer CoPt films.

전기도금법으로 제작한 CoPt 자성막의 자기상호작용과 자기적 성질

전기도금법으로 제작한 CoPt 자성막의 두께가 자기상호작용과 자기적 성질에 미치는 영향을 잔류자기화 곡선과 자기이력 곡선을 측정 분석하여 규명하였다. CoPt 자성막의 두께가 증가함에 따라 수직 보자력과 포화자화가 증가하였으나 각형비는 급격히 감소하였다. 잔류자화 곡선의 분석결과로부터 모든 시료의 주된 자기상호작용 기구는 쌍극자 상호작용이며, 시료의 두께가 증가함에 따라 상호작용의 세기가 증가함을 알 수 있었다. The influence of thickness on magnetic interaction and magnetic properties in electrodeposited CoPt magnetic films was investigated from the analysis of the magnetic remanence curves and the magnetic hysteresis loops. As the thickness of the CoPt film is increased, the perpendicular coercivity and the saturation magnetization are increased but the squareness is considerably decreased. The analysis results of the magnetic remanence curves and the magnetic hysteresis loops exhibited that the dipolar interaction is the main interaction mechanism for all samples, but the strength of the dipolar interaction gradually increased with increasing sample thickness.

Formation of L1 with (001) texture in magnetically annealed Co/Pt multilayers

The effect of magnetic annealing on the texture is investigated in a series of CoPt films of different thickness obtained by annealing of Co/Pt multilayers. Magnetic field is found to promote the (001) texture by selective (001) grain growth driven by the magnetic field and biaxial strain. A systematic correlation between in-plane biaxial strain and the degree of (001) texture is found only for the magnetically annealed samples.

Microstructures and Magnetic Properties of ${\rm CoPt{-}SiN}_{x} {-}{\rm Ag}$ Granular Thin Films With Ag Underlayer

When the Ag layer was introduced under the CoPt alloy film which annealed at 700°C, the CoPt/Ag films had large out-of-plane squareness ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> ), out-of-plane coercivity ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c⊥</sub> ), and saturation magnetization ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ). They were 0.95, 1432 kA/m, and 390 emu/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , respectively. Further, the SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ceramic materials were cosputtered with CoPt on the Ag underlayer at room temperature and then annealed to reduce the grain size of CoPt films. From the field-emission gun high-resolution transmission electron microscope analysis, the particle size of CoPt was about 10 nm as the SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> content was 46.2 vol.%. Furthermore, Ag was added into the CoPt-SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> films to reduce the transformation temperature of CoPt films from face-centered-cubic to face-centered-tetragonal structure.

Unusually Large Magnetic Anisotropy in Electrochemically Deposited Co-Rich Co–Pt Films

Co-rich Co-Pt films grown by electrodeposition from an amino-nitrite/citrate/glycine electrolyte onto Au(111) substrates apparently grow with a hexagonal structure, with its c-axis directed perpendicular to the surface. The films exhibit a perpendicular magnetic anisotropy (MCA) of the same order of magnitude as the shape anisotropy. Experimental estimates of the MCA result in a higher anisotropy than that reported for bulk materials of the same composition, but similar to values measured in films grown by vacuum methods at relatively high temperature, which partly consist of a high anisotropy, metastable orthorhombic Pmm2 phase. Comparison of valence band X-ray photoelectron spectroscopy measurements on electrodeposited films with density functional theory simulations of the electronic structure of the various reported Co(3)Pt structures support the notion that the films may consist of a mixture of the hexagonal and the Pmm2 structure.

Low temperature growth of FePt and CoPt films on MgO(111) substrate

Equiatomic CoPt and FePt thin films grown on MgO(111) substrates at temperatures (Ta) from room temperature (RT) to 400 °C were studied. Distinct phase evolution was observed. In CoPt films, a metastable phase of L11 appears at Ta = 250 °C prior to the formation of thermodynamic equilibrium L10 phase; whereas no intermediate structure is found in the FePt films. Good epitaxial growth of CoPt films can be obtained at low Ta before ordering. However, in FePt films, high quality epitaxy appears after the occurrence of L10 ordering. Either L11 or L10 ordering induces magnetic hardening. Perpendicular magnetic anisotropy was obtained in the L11 films, yet the L10 sample exhibited isotropic magnetism. Corresponding evolution in magnetic domain structure was also reported.

Highly chemical ordered L11 CoPt (111) films with perpendicular anisotropy grown on glass substrates

In this study, L11 CoPt (111) films were deposited on glass substrates at 300 °C with observed superlattice (111) and (333) peaks and easy axis distribution of 2°. The magnetic anisotropy constant was in the order of 107 erg/cm3. The effect of CoPt layer thickness on domain structure and magnetic properties was investigated. With increasing film thickness, the squareness was reduced and the nucleation field changed from negative to positive, indicating low impedance to domain wall motion and increased demagnetizing energy. Magnetic force microscopy images demonstrated the magnetic domain structure changed from irregular and large domains to highly interconnected stripes with increasing CoPt layer thickness.

Influence of Magnetic Domain of Perpendicular Anisotropy Master Medium on Printing Characteristics

The influence of the magnetic domain of the perpendicular anisotropy master medium (PAMM) on printing characteristics is analyzed by using micromagnetic simulation. As a result, when AC-erased CoPt film makes contact with the recording layer, the magnetization of the recording layer is reversed at the position corresponding to the domain wall of the CoPt film. However, the magnetic domain has no effect on the printing characteristics in the actual printing process.

Influence of domain of perpendicular anisotropy master medium on perpendicular magnetic printing

Magnetic printing is a promising way to write servo signals with high speed, high accuracy and low cost to fulfill the requirements for high-density hard disks. The PAMM (Perpendicular Anisotropy Master Medium) with CoPt magnetic layer has been proposed in order to improve the printing characteristics. However, it is worried that maze domain of the CoPt film may be printed on the hard disks. In this study, influence of the domain of the PAMM on the printing characteristics is analyzed by using micromagnetic simulation. As a result, it is clarified that the maze domain is not printed on the recording layer in the actual printing process even if the CoPt film has maze domain structure without external field.

Effects of annealing temperature, atomic composition, film thickness on structure and magnetic properties of CoPt composite films

L1 0–CoPt was obtained by annealing the CoPt film at 600 °C after co-sputtering Co and Pt targets in a magnetron sputtering system. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results showed a transformation from the face-centered-cubic (FCC) structure to the L1 0 ordered structure during the post-deposition annealing. Thermal stress ( S T), intrinsic stress ( S i) and total stress ( S total) in the films decreased with the increase of the annealing temperature. When the Co atomic composition was 50%, the coercivity of the CoPt film reached to a giant value, around 6300 Oe. The stress was released when the film thickness increased. The relaxed residual stress accounted for the enhancement in the coercivity. Magnetization reversal mechanism of the Co 50Pt 50 film followed neither the S–W model nor the DWM model.

Correlation of crystallographic structure and magnetic properties of electrodeposited Co-rich Co-Pt films

Co-rich Co-Pt alloy films have been grown by electrodeposition on Au buffer layer. Detailed texture measurements have been performed in order to understand the dependence of magnetic properties on phase composition and texture. X-ray analysis in Bragg-Brentano geometry shows that films seem to consist of hexagonal closed packed (hcp) or fcc phase. Due to similar lattice spacing of the densely packed planes of both possible phases, the (111) fcc and (002) hcp planes of Co-Pt and also the higher order reflections coincide. As a result, the information supplied by X-ray diffraction was of limited value. Hence pole figure measurements are used which determine the directional distribution of planes with a selected spacing. Here we present an approach to use pole figure measurements for phase identification. We show that this method allow a direct correlation with the magnetic properties, in particular with the magnetocrystalline anisotropy and magnetic texture.

Effect of Thicknesses on the Microstructure and Magnetic Properties of CoPt Thin Films

The microstructures and magnetic properties of CoPt thin films with thicknesses between 1 and 20 nm deposited on amorphous glass substrate and post-annealing at 600°C for 30 min were investigated. The morphology of CoPt thin film would change from a discontinuous nano-size CoPt islands into a continuous film gradually as the film thickness was increased from 1 to 20 nm. The formation mechanism of the CoPt islands may be due to the surface energy difference between the glass substrate and CoPt alloy. Each CoPt island could be a single domain particle. This discontinuous nano-island CoPt recording film may increase the recording density and enhance the signal to noise ratio while comparing with the continuous film. The as-deposited 5 nm CoPt film revealed the separated islands morphology after annealing at 600°C for 30 min. This nano-size CoPt thin film may be a candidate for ultra-high density magnetic recording media due to its discontinuous islanded nanostructure.

Effects of layering and magnetic annealing on the texture of CoPt films

The effect of magnetic field annealing of magnetron sputtered CoPt alloy films and Co/Pt bilayers on the crystallographic texture of the obtained chemically ordered (L1 0) CoPt films is presented. In CoPt alloy films the main effect of the magnetic field is to suppress (1 1 1) growth in the early stages of L1 0 formation whereas the development of (0 0 1) versus (1 0 0) texture is related to chemical ordering strain. A higher degree of (0 0 1) texture is obtained by magnetically annealing Co/Pt bilayers since the initial (1 1 1) texture in the as-sputtered films is avoided and Co–Pt alloying occurs in the presence of the magnetic field.

Thickness dependence of microstructures and magnetic properties for CoPt/Ag nanocomposite thin films

Ag underlayer (30 nm) has improved the degree of ordering and perpendicular magnetic anisotropy of CoPt films (7.5–10 nm). After annealing at 600 °C and 700 °C, the perpendicular coercivity of CoPt/Ag films has been raised as the thicknesses of CoPt layers are increased. The magnetic easy axis of CoPt/Ag films would change from a random orientation to an out-of-plane orientation. It is found that Ag underlayer with thickness of 30 nm can improve the perpendicular magnetic properties of CoPt layers with thicknesses in the range of 7.5–10 nm. The CoPt/Ag films would be a candidate for perpendicular magnetic recording media.

Magnetic properties of nanocrystalline CoPt electrodeposited films. Influence of P incorporation

Platinum-rich CoPt films have been electrodeposited with the aim of preparing hard magnetic films on silicon-based substrates without the need for subsequent annealing. Electrodeposition conditions have permitted the crystalline structure of the films to be controlled. Pt percentages of up to 60–65 wt.% have been attained while maintaining the hexagonal Co phase, leading to CoPt films with moderate coercivity and good corrosion resistance. However, when low deposition potentials were used, CoPt films with higher Pt percentages were obtained, but in this case, the films exhibited an fcc structure, having lower coercivity and less corrosion resistance. The presence of hypophosphite in the solution limited the platinum percentage in the deposited CoPtP films, but an hexagonal close-packed (hcp) structure was always observed in this case. The incorporation of P into the deposits led to increases in both the coercivity of the films and the corrosion resistance of the coatings, with respect to pure CoPt. The highest coercivity was obtained for hcp CoPtP deposits with 40 wt.% of Pt.

Evidence for nanoscale two-dimensional Co clusters inCoPt3 films with perpendicular magnetic anisotropy

The length scale of the local chemical anisotropy responsible for thegrowth-temperature-induced perpendicular magnetic anisotropy of face-centered cubicCoPt3 alloy films was investigated using polarized extended x-ray absorption fine structure(EXAFS). These x-ray measurements were performed on a series of four (111)CoPt3 films epitaxially grown on (0001) sapphire substrates. The EXAFS data show a preferencefor Co–Co pairs parallel to the film plane when the film exhibits magnetic anisotropy, andrandom chemical order otherwise. Furthermore, atomic pair correlation anisotropy wasevidenced only in the EXAFS signal from the next neighbors to the absorbing Co atomsand from multiple scattering paths focused through the next neighbors. This suggests thatthe Co clusters are no more than a few atoms in extent in the plane and onemonolayer in extent out of the plane. Our EXAFS results confirm the correlationbetween perpendicular magnetic anisotropy and two-dimensional Co segregation inCoPt3 alloy films, and establish a length scale on the order of 10 Å for the Co clusters.

Effect of underlayer (Pt, Ru, Au, Ag) on L1 1 ordering in sputtered CoPt thin films

CoPt films without and with underlayers of Pt, Ru, Ag or Au were deposited on MgO(1 1 1) substrates by magnetron sputtering at 350 °C. Using a Pt underlayer resulted in an epitaxially grown Ll1 structure with enhanced chemical ordering, a high perpendicular anisotropy energy of 2.1 × 106 J m–3, and an anisotropy field of 2.4 MA m−1 at 4 K, which reduces the Ll1 ordering temperature to under 200 °C and produces a room-temperature anisotropy field that exceeds 1.6 MA m−1, indicating potential application for magnetic recording.

Magnetoresistance of perpendicularly magnetized tunnel junction using L10-CoNiPt with low saturation magnetization

Investigations of the structural and magnetic properties of thin Co50-xNixPt50 (x = 0, 10, 15, 37.5) films and fabrication of magnetic tunnel junctions (MTJs) using Co50Pt50 and Co35Ni15Pt50 electrodes were performed. X-ray diffraction analyses revealed that 20-nm-thick CoPt and CoNiPt films were epitaxially grown with (001)-orientation with an L10-chemical order parameter of 0.66–0.82. CoNiPt with various Ni contents magnetized perpendicularly; the saturation magnetization reduced to 157 emu/cm3 when the Ni content was increased to 37.5%. Magnetotransport measurements under a magnetic field applied perpendicular to the film plane revealed a tunnel magnetoresistance ratio of 10% and 1% at 10 K and 300 K, respectively, for MTJ using Co35Ni15Pt50 electrodes.

Magnetic and structural properties of L11 type CoPt-C ordered alloy perpendicular films as a function of C content

Magnetic and structural properties of L11 type (Co0.5Pt0.5)100-X-CX ordered alloy perpendicular films, fabricated on 2.5 inch size glass disks by sputter deposition, were examined as a function of C content, X. L11 type Co0.5Pt0.5-C polycrystalline films (10 nm thickness), with <111> axis (the easy axis) perpendicular to the film plane, were successfully fabricated even for a 30 vol% C content. Structural analysis indicated the segregation of C to the grain boundaries. Uniaxial magnetic anisotropy, Ku, of Co0.5Pt0.5 films without C addition was relatively low, about 1.5x107 erg/cm3 under the present deposition conditions. However, the addition of 5 vol.% C to Co-Pt films enhanced the ordering, resulting in an increase in Ku to around 2.5 x107 erg/cm3. A further increase in C content reduced Ku; however, Ku maintained a relatively large value of about 1.8x107 erg/cm3 even for a 20vol% C content, without degrading the easy axis orientation perpendicular to the film plane. Experimental results demonstrated the potential of the L11 type Co0.5Pt0.5-C films for use in granular media applications, due to their very high Ku, the relatively low fabrication temperature, and good controllability of the grain orientation.

Depth dependent local structures in CoPt thin films

X-ray absorption spectroscopy (XAS) has been used to clarify the thickness-dependent magnetic properties in nanometric CoPt films. We get benefit from the variation of the sampling depth with the grazing angle to investigate the variations of the local order within the film. In order to properly resconstruct the 3D information the experiments were performed either in the in-plane as in the out-of-plane geometries and supported by ab initio calculations. A depth dependence in the chemical order is revealed and the magnetic behavior is interpreted within this framework.