Structural and magnetic characterization of very thin CoCr films

Abstract

In this paper we describe the nucleation and growth o~ thin Co-Cr layers on different substrates and seedlayers. Especially the presence and formation of the initial layer is considered, and corresponding growth mechanisms are proposed. The magnetic properties of these layers have been analyzed by in-plane VSM and by anomalous Hall effect (AHE) measurements. Even layers as thin as 5 nm are shown to exhibit a perpendicular magnetic anisotropy. For a high coercive Co-Cr film the formation of dot-like domains is shown by the Bitter-colloid/SEM technique.

Magnetic microstructure of sputtered Co-Cr films

“…In the x-direction large domains are observed, while the y-direction is characterized by a ripple structure. Such a ripple structure in a soft-magnetic layer is often attributed to (in-plane) random anisotropy variations; this is consistent with our electron diffraction experiments [2]. The difference in induction patterns in x-and y-directions may well originate from the way of ac demagnetization of the specimens, where the axis of rotation in the decreasing dc field was about parallel to the x-direction, so that the effective ac field in the x-direction was very small; the demagnetization in this direction was therefore not complete.…”

“…Although the way of demagnetization was similar for the 75 nm thick specimen, no difference in x-and y-induction was observed in the overall structure at low magnification. This is attributed to the fact that locally the easy direction of magnetization has come out of the plane of the specimen through the crystalline anisotropy, as interpreted from the increased intensity of the crystal planes (relative to thinner layers) in the [100] direction in the electron diffraction experiments [2]. Now the effective ac field acting in the direction of magnetization is larger, leaving a better demagnetized specimen.…”

“…[7]. From bright-field TEM images it is known that the crystal size varies from about 10 nm diameter for the 10 nm thick layer to about 30-50 nm diameter for the 75 nm thick layer [2]. Finally, the dispersion of the (002) crystal planes, A050 , was too large to be detectable for the thinner layers, and is about 15 ° for the layers thicker than 50 nm.…”

“…The H e ±/H k values indicate the type of magnetization reversal [5]; small values are typical for domain wall displacement reversal, while high values (> 10%) are characteristic of reversal through a rotational mode, exhibiting dot-like domains. From the in-plane remanence ratios (Mr/Ms)zL it is seen that even the thicker layers still exhibit a significant initial [2] showed that in the thinnest layers (thickness < 25 nm) a certain amount of hcp phase with in-plane orientation of the c-axis is present, as indicated by the (101) and (002) diffraction rings. At thicknesses above 50 nm the crystallites tend to become oriented perpendicular to the film plane, as seen from the (100) direction ring, leaving a relatively minor fraction in the in-plane directions, as also reported in ref.…”

“…The Co81Cr19 layers investigated in this paper have been rf-sputter-deposited on 40 nm thick Si3N 4 membranes [2]. The hysteresis curves are measured by a VSM.…”