S. de Haan

Simulations of the magnetization reversal of clustered Co-Cr particles

Micromagnetic simulations of the magnetization reversal of clusters of 9 and 25 magnetostatically coupled Co-Cr particles are presented. The magnetostatic interaction between neighbouring particles facilitates reversal. The non-uniform magnetization configuration plays an important role in this effect.

Reversible Magnetization-Rotation in Sub-Micron Co-Cr Samples: Measurements and Micromagnetic Simulations

The magnetization reversal of Co-G with perpendicular anisotropy is studied by anomalous Hall effect measurements and by micromagnetic simulations. In a measured hysteresis loop of a 300 nmX300 nm sample (consisting of approximately 40 columns of Co-G), discrete jumps are observed, together with a more or less continuous change in magnetization, the latter with both positive and negative sign. The continuous and discrete parts of the hysteresis loop are separated to extract micromagnetic information from the anomalous Hall measurement. The discrete jumps are attributed to parts of columns that switch irreversibly, the continuous magnetization change is attributed to reversible rotation, partly of volumes with in-plane anisotropy. These assumptions are checked by means of a micromagnetic model.

Magnetisation reversal mechanism in Co-Cr media for perpendicular magnetic recording

In this study Co---Cr thin films with perpendicular anisotropy are investigated. Three films with values for Hc of 11, 90 and 170 kA/m have been selected for this paper. Besides the coercivily several other parameters such as the Hc/Hk, Cr-segregation, domain structure, column sizes, etc. were studied by VSM, SEM, NMR, MFM, AFM and selective etching. The anomalous Hall effect (AHE) has been used to record the hysteresis curves of submicron Hall crosses. This very sensitive technique in combination with e-beam lithography and ion-beam etching resulted in the recording of AHE hysteresis loops with dimensions of the Hall crosses as small as 0.3 × 0.3 ?m2. The AHE loops of three samples, with less than 60 columns, show different micromagnetic properties. Only the sample with Hc1 = 90 kA/m shows clear steps in the curves above the noise level. The largest steps correspond with the reversal of one column and the total number of steps was five times the number of columns for this sample. The different reversal mechanisms observed by the AHE are related to the differences in structure, coercivity and domain size.

Reversal studies on sub-micron Co-Cr thin films by AHE analysis

In this study three Co---Cr thin films, prepared under different deposition conditions, are investigated. They have values for the coercivity (Hc) of 11, 90 and 170 kA/m, respectively. The anomalous Hall effect (AHE) has been used to record the hysteresis curves of specially prepared sub-micron Hall crosses. With this very sensitive technique the hysteresis loops were recorded of samples with Hall cross dimensions as small as 0.3 × 0.3 ?m2. The AHE loops of the samples, with less than 60 columns, show different `meso-magnetic? properties. Only the sample with Hc = 90 kA/m shows large steps in the curves above the noise level. The largest steps correspond with the reversal of one column. In this case the number of steps was 5 times the number of columns. From these measurements we conclude that the basic switching unit is smaller than one column. Furthermore the AHE results confirm that the low and the high coercive films reverses by domain wall motion and rotation respectively. The sample with Hc = 90 kA/m switches with a combination of these two reversal mechanisms.