Future Recording Media Research Articles

ChemInform Abstract: Magnetic Nanoparticles: a Subject for Both Fundamental Research and Applications

AbstractReview: 167 refs.

Magnetic Nanoparticles: A Subject for Both Fundamental Research and Applications

Single domain magnetic nanoparticles (MNPs) have been a vivid subject of intense research for the last fifty years. Preparation of magnetic nanoparticles and nanostructures has been achieved by both bottom‐up and top‐down approaches. Single domain MNPs show Néel‐Brown‐like relaxation. The Stoner‐Wohlfarth model describes the angular dependence of the switching of the magnetization of a single domain particle in applied magnetic fields. By varying the spacing between the particles, the inter‐particle interactions can be tuned. This leads to various supermagnetic states such as superparamagnetism, superspin glass, and superferromagnetism. Recently, the study of the magnetization dynamics of such single domain MNPs has attracted particular attention, and observations of various collective spin wave modes in patterned nanomagnet arrays have opened new avenues for on‐chip microwave communications. MNPs have the potential for various other applications such as future recording media and in medicine. We will discuss the various aspects involved in the research on MNPs.

Magnetization Reversal in Arrays of Magnetic Nanoperforations

Nanoperforated ZrO2 membranes, produced via organic/inorganic self-assembly using block copolymer micelles, serve as template for a Co/Pt multilayer stack with out-of-plane magnetic anisotropy. The deposition of the magnetic film results in an array of magnetic nanodots surrounded by a continuous magnetic film. These magnetic dots are found to be in a single-domain state and appear as magnetically exchange isolated from the surrounding film. The latter observation can be related to the specific morphology of the nanoperforations. In addition, strong domain-wall pinning of the continuous magnetic film at the locations of the nanoperforations was observed. Therefore, this approach is promising to create a percolated magnetic medium, which is considered as future recording media.

Perpendicular magnetic anisotropy of CoPt–AlN composite film with nano-fiber structure

Co-Pt-AlN films were prepared by sputtering a Co-Pt-Al composite target in Ar + N 2 atmosphere. Upon thermal annealing at elevated temperatures, fcc CoPt and a-AlN are formed in the films as phases separated from one other. Both phases develop as fiber-like columnar grains vertical to the substrate and with their lateral size less than 10 nm. Because of the shape anisotropy of the magnetic fiber grains the CoPt-AlN film shows a perpendicular magnetic anisotropy at a thickness equal to or larger than about 25 nm while the Co-TiN [6] and CoPt-TiO 2 [11] films do not unless their thicknesses reach 50 and 100 nm, respectively. This suggests that both the shape anisotropy of the CoPt magnetic fiber grains and their mutual separation in an a-AlN medium work more effectively in the formation with the perpendicular magnetic anisotropy. Such a perpendicular magnetic anisotropy of the CoPt-AIN film associated with the nano-scale feature makes it a very promising candidate for future recording media with ultra-high area density.

Electrodeposition of highly uniform magnetic nanoparticle arrays in ordered alumite

We report the fabrication of nanometer scale ordered arrays of magnetic cylindrical nanoparticles with low aspect ratio (height/radius a=0.2–7) and ultrahigh uniformity. Anodization and electrochemical deposition are employed for template synthesis and metal particle growth, respectively. Particle uniformity is achieved by an electrodeposition scheme, utilizing pulse reverse voltage wave forms to control nucleation and growth of the particles. The resulting nanoparticles are polycrystalline and grains are randomly oriented. The magnetic properties of the array are dominated by particle shape and by interparticle magnetostatic interactions. A very clear transition of the anisotropy from perpendicular to in plane is observed at an aspect ratio a of about two. The arrays exhibit good thermal stability, demonstrating a great potential of these structures as future recording media in a patterned scheme. The pulse reverse electrodeposition technique shows great promise for the synthesis of nanostructures of various nature.

Corrosion behavior of high coercivity FeSmN thin films for longitudinal magnetic recording media

The corrosion behavior of high coercivity FeSmN compound films is compared with reference samples in a 80/spl deg/C/80% relative humidity accelerated test environment. FeSm films were deposited onto heated substrates by dc magnetron sputtering and then annealed in-situ in nitrogen to form FeSmN. The results showed that the nitriding process remarkably improved the corrosion resistance and that FeSmN was more stable than commercial Hi8 metal evaporated and metal particle tapes. The conclusions are supported by separate electrochemical potentiodynamic polarization measurements. The relative stability of FeSmN combined with its excellent magnetic properties, as we reported earlier, makes the material an attractive choice for future recording media.