High magnetic, transport, and optical uniaxial anisotropies generated by controlled directionally grown nano-sheets in Fe thin films

Abstract

Fe films with thicknesses between 17 and 95 nm were grown with a nano-sheet morphology, which enabled their high uniaxial magnetic, transport, and optical in-plane anisotropies. The top edge of the nano-sheets was directly visualized as nano-string-like structures of approximately 12.5–14 nm width and 100–300 nm length. The hysteresis loops showed a clear easy direction of magnetization in the longitudinal direction of the nano-sheets, whereas the hard direction loops were anhysteretic, with no remanence and zero coercive field. The anisotropy field exhibited values between 70 and 111 kA/m depending on the thickness of the films, with the maximum value corresponding to a 34 nm thick sample. The resistance of the films was also found to be highly anisotropic. The ratio (R⊥–R||)/R|| was ≈86%, with R|| and R⊥ being the resistances in the parallel and perpendicular directions of the nano-sheets, respectively. Likewise, the reflectivity of the samples behaved anisotropically; the ratio (IReflmax–IReflmin)/IReflmax of the intensity of reflected light by the films reached up to 61% for 34 nm thick samples, achieving the maximum value, IReflmax, when the plane of the incident light coincided with the direction of the nano-sheets and the minimum, IReflmin, when this plane was perpendicular to the direction of the nano-sheets. The origin of these anisotropic behaviors was established. These anisotropic films with high magnetization and high uniaxial anisotropies at the nanoscale can be useful for microelectronics applications, for devices such as magnetic sensors and transducers, or for ultrahigh frequency inductors.