Magneto-mechanical Effect of NiFe Thin Films Depending on the Intrinsic Magnetic Anisotropy

Abstract

Verifying magnetic anisotropy is essential for developing flexible magnetic devices. The magneto-mechanical effect is a unique phenomenon in magnetic materials for bending geometries and produces the stress magnetic anisotropy depending on the stress direction and its magneto-striction coefficient. In addition, the fabrication process for the flexible magnetic devices, such as deposition, annealing, and patterning, significantly causes the intrinsic magnetic anisotropy to change the reversal behaviors in the devices. This study investigated the variation of the stress magnetic anisotropy in the flexible NiFe (permalloy) thin films as a function of the bending repetition and its direction when the thin films had a different easy axis caused by the sputtering process. The variation of the stress magnetic anisotropy was observed by the magnetization reversal behaviors and the typical ferromagnetic resonance field detection before and after the application of the tensile stress. The stress effect was exponentially accumulated with increasing bending repetition on the thin film in both samples. However, when the repeated stress was applied in alternating x- and y-directions, minor resonance field fluctuation was observed in the film, which had the tilted intrinsic magnetic anisotropy. This result indicated that intrinsic magnetic anisotropy during the fabrication process played an essential role in determining the amount of effective field for designing flexible magnetic devices.