P. Krone

L10 FePt based exchange coupled composite bit patterned films

We demonstrate a 2.5-fold coercivity reduction in FePt based exchange coupled composite bit patterned media (ECC-BPM) by coupling a lower anisotropy Co/Pd–Co/Ni-multilayer system to the top of a high anisotropy FePt L10 film. Furthermore the tight switching field distribution (SFD) of the lower anisotropy system reduces the SFD of the ECC-BPM composite system compared to a single layer FePt film. The relative amount of switching field and SFD reduction in these ECC-BPM arrays agree with corresponding micromagnetic simulations.

Exchange coupled composite bit patterned media

A micromagnetic study on the magnetization reversal in bit patterned media (BPM) with each bit consisting of an exchange coupled composite (ECC) layer stack is presented. The simulations reveal superior magnetic properties of the combined ECC/BPM scheme, in particular for graded media, using uncorrelated distributions of magnetic anisotropy values in order to lower the switching field while keeping a high thermal stability of the media. In this study, a route for narrowing the switching field distribution of the bit array is provided as well, which is vital for the applicability of the BPM concept in magnetic data storage.

Effect of the anisotropy distribution on the coercive field and switching field distribution of bit patterned media

We present a systematic study on the magnetization reversal in square arrays of magnetic nanostructures. To account for the unavoidable inhomogeneities of the magnetic properties due to, i.e., template preparation, a distribution of magnetic anisotropy values was taken into account. We show that the variation in magnetic anisotropy within an array of magnetic nanostructures and the influence of magnetic dipole-dipole interaction between the individual bits with separation distance is crucial for the performance of bit patterned media (BPM) concerning in particular the switching field distribution (SFD). Interestingly, a narrowing of the SFD was found with the angle between the direction of the external magnetic field and easy axis of magnetization, which is an important aspect for the usability of BPM with tilted anisotropy at ultrahigh storage densities beyond 1 Tbit/in.2.

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.

Magnetic properties of granular CoCrPt:SiO 2 thin films deposited on GaSb?nanocones

We report on the effect of microstructure and geometrically induced modifications of the magnetic properties of granular CoCrPt:SiO2 films with weakly interacting magnetic grains deposited on pre-structured GaSb nanocone templates fabricated by an ion erosion technique. By tuning the irradiation conditions, nanocone patterns of different cone sizes were prepared (from 28 to 120 nm in diameter and 32 to 330 nm high, respectively). The influence of the intergranular exchange coupling was also investigated by varying the SiO2 content from 8 to 12 at.%. Deposition of CoCrPt:SiO2 on samples with small nanocones leads to a close magnetic grain packing, which results in the formation of extended magnetic domains larger than the average distance between the GaSb cones. In contrast, on larger nanocones, the magnetic coating grows on the side-walls, with a large separation between neighboring cones, leading to magnetic single-domain regions, which are correlated to the underlying structure. Magnetometry indicates that both remanence and coercivity decrease with increasing cone size and/or SiO2 content due to a combined effect of the angular distribution of the magnetic easy axis of the grains and the intergranular exchange coupling strength.

Spin dynamics of magnetic nanostructures investigated by micromagnetic simulations

Micromagnetic simulations were performed to investigate the spin dynamics of cylindrical magnetic nanostructures of various sizes down to 20 nm. The presented simulation technique provides information on the equilibrium states, magnetization precession, and spatial distributions of excited spin wave modes of individual nanostructures. Larger cylindrical nanostructures reveal a flower state magnetization configuration and show rather complex edge and center modes, which depend strongly on the saturation magnetization. This behavior allows controlling the precession frequencies, which is important in microwave-assisted three-dimensional magnetic recording, where layers of different resonance frequency need to be addressed and switched individually.

Magnetization reversal of bit patterned media: Role of the angular orientation of the magnetic anisotropy axes

Micromagnetic modeling was performed to study the influence of an angular dispersion of the magnetic anisotropy axis on the reversal behavior of tilted bit patterned media with an areal density of about 1 Tbit/in.2. Thereby, the angular dispersion was realized by having the anisotropy axes of the individual bits lying on the surface of a cone with a specific opening angle. In addition, a distribution of the magnetic anisotropy value within the array of magnetic nanostructures was taken into account. The effect of the angular variation in the magnetic anisotropy orientation on the switching field distribution was investigated. Two optimized geometries were suggested in order to keep the switching field distribution as narrow as possible: (1) uniaxial perpendicular bits with the magnetic field applied under an angle of 45° and (2) tilting the anisotropy axis to about 45°–75° and applying a perpendicular magnetic field. However, mixing both situations results in a drastic increase in the switching field dist...

Correlation of magnetic anisotropy distributions in layered exchange coupled composite bit patterned media

A micromagnetic study of the magnetization reversal in bit patterned media (BPM) with each bit consisting of an exchange coupled composite stack with two strongly exchange coupled layers is presented. In this investigation, the influence of correlation between the values of the distributions of the magnetic anisotropy values of the individual layers on the magnetization reversal behavior of the individual layers in the stack is examined. It is shown that a partial correlation can narrow the switching field distribution of the bit array while the switching field remains unaffected, which is vital for the applicability of the BPM concept in magnetic data storage.

Nanocap arrays of granular CoCrPt:SiO2 films on silica particles: tailoring of the magnetic properties by Co + irradiation

An approach for tailoring the magnetic properties by ion irradiation of granular perpendicular CoCrPt:SiO(2) films grown on silica particles with sizes down to 10 nm was investigated. The as-prepared samples reveal an intriguing scaling dependence of the coercive field and remnant magnetization: both parameters are found to decrease with decreasing particle size. However, Co(+) irradiation at a low fluence of 0.5 x 10(14) cm(-2) already results in an opposite scaling behavior. It is assumed that this modification is due to the enhancement of the intergranular magnetic exchange coupling of the granular CoCrPt:SiO(2) film initiated by Co(+) irradiation resulting in a modified reversal behavior. Further increase of the irradiation fluence beyond 1.6 x 10(14) ions cm(-2) leads to a degradation of the magnetic layer properties, lowering the remnant magnetization and the coercive field in the easy-axis direction. Moreover, the local magnetic properties of the samples were analyzed by magnetic force microscopy revealing magnetic multi-domain cap structures.