SungMan Kim

Perpendicular Magnetic Anisotropy in FePt Patterned Media Employing a CrV Seed Layer

A thin FePt film was deposited onto a CrV seed layer at 400°C and showed a high coercivity (~3,400 Oe) and high magnetization (900–1,000 emu/cm3) characteristic of L 10 phase. However, the magnetic properties of patterned media fabricated from the film stack were degraded due to the Ar-ion bombardment. We employed a deposition-last process, in which FePt film deposited at room temperature underwent lift-off and post-annealing processes, to avoid the exposure of FePt to Ar plasma. A patterned medium with 100-nm nano-columns showed an out-of-plane coercivity fivefold larger than its in-plane counterpart and a remanent magnetization comparable to saturation magnetization in the out-of-plane direction, indicating a high perpendicular anisotropy. These results demonstrate the high perpendicular anisotropy in FePt patterned media using a Cr-based compound seed layer for the first time and suggest that ultra-high-density magnetic recording media can be achieved using this optimized top-down approach.

Effect of Sn addition on the microstructure and magnetic properties of FePt thin film

An attempt has been made in this study to incorporate an alloying element to lower the order-disorder transformation temperature of Fe–Pt alloy and the effect of Sn addition was investigated for this purpose. The coercivity of the FePtSn film is measured to be about 5000 Oe, whereas that of FePt film is several hundred Oe at the annealing temperature of 300 °C. Therefore, Sn addition is effective to promote the L10 ordering and reduce the ordering temperature of FePt alloy. Analysis of crystal structure by x-ray diffraction reveals that the lattice expansion of cubic FePt phase is induced by Sn addition in as-deposited film. After the annealing from 300 °C to 600 °C, L10 ordered phase is formed in FePtSn films and lattice constant of FePtSn film is approached to pure FePt with increasing annealing temperature up to 600 °C. Difference in solid solubility of Sn between disordered and ordered phase exists and thus excess Sn will diffuse out from ordered FePt L10 phase. Segregated Sn is found at the surface a...

The Effects of CrV Underlayer on the Structure and Magnetic Properties of FePt Thin Film

An attempt is made in this study to employ vanadium containing chromium (CrV) alloy underlayer to control the microstructure and ultimately to facilitate the in-situ ordering of Fe-Pt thin film. CrV alloys with V contents ranging from 0 to 15 at% were investigated to evaluate their effects on the magnetic properties and structural modification of FePt thin film. Addition of V in Cr underlayer results in the formation of FePt L10 phase with (001) preferred orientation. Analysis of XRD and HR-TEM results reveals that the lattice expansion of Cr underlayer induced by V addition increases the lattice misfit strain between CrV underlayer and FePt magnetic layer. Consequently well aligned FePt (001) grains and in-situ ordering of FePt L10 thin film can be obtained. Magnetic property measurements show that FePt/Pt/5.8 at.%V-Cr multilayer has the maximum out-of-plane coercivity (4000 Oe) and squareness (0.95). Due to in-situ ordering, good perpendicular magnetic properties with higher coercivity and squareness were achieved from FePt/Pt/Cr94.2V5.8 multi-layers at the processing temperature of 350°C without further annealing treatment.

Molecular dynamics simulation study of deposition and annealing behaviors of Al atoms on Cu surface

Deposition and annealing behaviors of Al atoms on rough Cu (111) surface were investigated on the atomic scale by three-dimensional classical molecular dynamics simulation. The rough Cu surface was modeled by depositing 5 ML of Cu on Ta (011) substrate. Most Al atoms deposited on the rough Cu surface placed on the atomic steps, preserving the major features of the surface during Al deposition. This behavior was discussed in terms of the smaller barrier of the surface diffusion than Ehrlich–Schwoebel barrier of Al on Cu (111) surface. By annealing at 700 K, significant intermixing between Al and Cu rapidly occurs with decrease in the surface roughness. This behavior reveals that the exchange process of Al with substrate Cu dominates during the initial stage of high temperature annealing.

Asymmetric intermixing in a Co-Al thin film system: An investigation using coaxial impact collision ion scattering spectroscopy

Surface structure evolution during atomic deposition in a Co–Al system was investigated using coaxial impact collision ion scattering spectroscopy (CAICISS). Half monolayer of Al and Co atoms were deposited on Co(0001) and Al(001) single crystal surfaces, respectively, in an ultrahigh-vacuum environment. CAICISS analysis of the deposited surface revealed an asymmetric interfacial reaction, as predicted by previous molecular dynamics simulations. Al atoms deposited on a Co substrate are placed on the surface with no interatomic intermixing. In contrast, significant surface intermixing with the deposited Co atoms occurs on the Al(001) substrate, resulting in the formation of a CoAl intermetallic surface layer of B2 structure. These asymmetric features would be important to the understanding of the structural evolution of thin film multilayers.

The Effects of the Pd-TiN Seed Layer on the Magnetic Properties of Co/Pd Multilayered Media

We investigated a Pd-TiN thin film as a seed layer for a [Co/Pd] multilayered perpendicular magnetic recording media. The 15-nm Pd-TiN thin film and [Co(0.2 nm)/Pd(0.8 nm)] multilayered media were fabricated by dc magnetron sputtering without heating the substrate. The Pd-TiN(20 vol.%) granular seed layer with apparent grain boundaries is considered to provide suitable seeds to [Co/Pd] multilayer and reduced the magnetic exchange coupling of [Co/Pd] grains causing an increase of the perpendicular coercive field and a decrease of the magnetic cluster size for the [Co/Pd] multilayered media. These results suggest that the Pd-TiN seed layer contributed to the formation of physically well-separated [Co/Pd] multilayered grains, improving the magnetic properties of [Co/Pd] multilayered media.

Improvement of Magnetic Properties and Texture of FePt Thin Films on MgO Substrates by Sn Addition

In this work, we studied the effects of Sn addition on the ordering temperature of FePt thin film. The coercivity of FePtSn film was about 1000 Oe greater than the coercivity of FePt film for an annealing temperature of 600℃. Therefore, Sn addition was effective in promoting the L1? ordering and in reducing the ordering temperature of the FePt film. From our X-ray diffraction results, we found that in the as-deposited film, the addition of Sn induced a lattice expansion in disordered FePt thin films. After the annealing process, the excess Sn diffuses out from the ordered FePt thin film because of the difference in the solid solubility of Sn between the disordered and ordered phases. The existence of precipitates of Sn from the FePt lattice was deduced by Curie temperature measurements of the FePt and FePtSn films. Therefore, the key role played by the addition of Sn to the FePt film can be explained by a reduction in the activation energy for the L10 order-disorder transformation of FePt which originates from the high internal stress in the disordered phase induced by the supersaturated Sn atoms.

Patterned Co/Pd multilayer structure for high-density magnetic recording media

For development of high-density magnetic recording media, superparamagnetism due to thermal instability has been a main problem in make the density limitations. One of the most promising methods to overcome superparamagnetism is the use of patterned media. Particularly, Co/Pd multi-layer has been one of the significant materials for high-density magnetic recording media. In this study, we fabricated the patterned Co/Pd multilayer structures using electron-beam lithography and a dry etching technique and investigated the magnetic properties of the patterned structures