Journal of the Magnetics Society of Japan

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Co-Pt alloy films were sputtered on (111)- and (100)- oriented Pt underlayers. The crystal structure was analyzed by means of X-ray pole figure measurements. On (111)-oriented Pt underlayers, the crystal structure of Co-Pt alloy film was (0001)-oriented hcp when the Pt content was less than 40%, but changed to (111)-oriented fcc when the Pt content exceeded 50%. In the region between 40% and 50%, both hcp and fcc structures existed. On the other hand, the Co-Pt alloy films on (100)-oriented Pt underlayers had a (100)-oriented fcc structure. Torque measurements revealed that the perpendicular anisotropy constant K_u was relatively small in the films with the (111)- or (100)-oriented fcc structure. However, K_u was quite large in the films with the (0001)-oriented hcp structure, reaching 0.7 MJ/m³ at a Pt content of about 30%. The perpendicular anisotropy seems to originate in the crystalline anisotropy of the hcp Co-Pt alloy.

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It was found that the magnetic circuit approach, which is useful in situations where magnetic flux is interrupted by air gaps, is also helpful in illustrating magnetic shielding. Equivalent magnetic circuits of single and multiple cylindrical shields were developed and analyzed. Simple and explicit equations describing the shielding factors in terms of the reluctances of the shielded area, the shells themselves, and the spaces between them were obtained. To simplify evaluation of corresponding reluctances, flux density is assumed to be distributed uniformly throughout the shield parts, including the shells and the spaces between them. The resulting equations exactly reproduce well-known approximate analytical formulas. An important advantage of the proposed method over numerical ones is that it allows a straightforward physical insight into the shielding problem.

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