Abstract
CoCrTa/Cr/Al and CoCrTa/Cr thin films were deposited on glass substrate at 280 °C using dc magnetron sputtering. The coercivity of CoCrTa/Cr films increased by introducing an Al underlayer. In 500 Å CoCrTa/Cr films, the coercivity increased with increasing Cr thickness and saturated above 700 Å Cr thickness (Hc=1050 Oe). On the other hand, in 500 Å CoCrTa/Cr/700 Å Al films, the coercivity increased sharply with increasing Cr thickness and showed a maximum value at 700 Å Cr thickness (Hc=1380 Oe). The coercivity squareness of the CoCrTa/Cr/Al and CoCrTa/Cr films was increased with increasing Cr thickness. The coercivity squareness of CoCrTa/Cr/Al films was lower than that of CoCrTa/Cr films. To study the origin of coercivity enhancement in CoCrTa/Cr films when deposited on an Al underlayer, microstructures of the two films were investigated using transmission electron microscopy (TEM). We controlled grain sizes of CoCrTa films by changing the thickness of the Cr layer. The grain size of CoCrTa films increased with increasing Cr thickness. The coercivity of CoCrTa/Cr/Al films showed a maximum value at a grain size of 430 Å. These results suggest that the transition from single domain to multidomain could occur at a grain size of ∼400 Å. To understand the coercivity squareness changes by the introduction of an Al underlayer, the angular variation of coercivity was measured. The magnetization of CoCrTa/Cr films was reversed by domain wall motion. On the other hand, by the incorporation of an Al underlayer, the angular variation of coercivity deviated from the domain wall motion mode. Cross-sectional TEM studies of CoCrTa/Cr/Al films showed that Cr atoms in Cr layers diffused into an Al underlayer and Al atoms were detected in both Cr and CoCrTa layers, but magnetization of the magnetic layer was not decreased. The decrease in coercivity squareness of CoCrTa/Cr/Al films would be attributed to magnetic decoupling by segregation of Al atoms in grain boundaries of CoCrTa films.
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