Nd-Fe-B/Ta永久磁石多層薄膜の耐熱特性

概要

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Nd-Fe-B/Ta multilayered permanent-magnet thin films that were perpendicularly anisotropic were prepared by magnetron sputtering, and their thermal stability was estimated in terms of the irreversible flux loss after a heat cycle. In the multilayered films, an Nd2Fe14B phase crystallized, and its grain size was successfully controlled by the thickness of the single Nd-Fe-B layer. We found that heatproof temperature, defined as a point where the irreversible flux loss reached −5%, advanced as the grain size of Nd2Fe14B was reduced. The heatproof temperature demonstrated an intimate correlation with the reverse field of a knee point occurring in the second quadrant of the J-H curve measured at room temperature. It was suggested that the knee point drifted with a rise in temperature, and once the knee point crossed the load line, irreversible flux loss occurred. The intimate correlation between the knee-point field and the heatproof temperature implied that the temperature coefficient of the knee-point field differed little between the films. Despite the strong effect of demagnetization in the out-of-plane direction of thin film magnets, excellent thermal stability with the heatproof temperature exceeding 150°C was obtained in the multilayered thin films with a single Nd-Fe-B layer thickness of 200 nm.
社団法人　日本磁気学会の論文
2009-05-01