Magnetic properties of textured NiFe(111) and NiFe(200) films

Thickness dependencies ($d\approx 20$–$370$ nm) of the saturation magnetization $4\pi M$, the ferromagnetic resonance linewidth $\Delta H$, the coercivity field $H_c$ and the shape of hysteresis loops were investigated for Ni$_{80}$Fe$_{20}$ (NiFe) films with (200) texture. The thickness dependencies of magnetic parameters for NiFe(200) films were compared with the dependencies $4\pi M(d)$, $\Delta H(d)$ and $H_c (d)$ for NiFe(111) films with strong (111) texture and polycrystalline NiFe films. Materials and Methods: NiFe(200) films were $d_c$-sputtered at the substrate temperature $T_s \approx 570$ K without substrate bias voltage ($U_b\approx 0$). NiFe(111) films were $d_c$-sputtered at the substrate temperature $T_s\approx 300$ K and two values of the substrate bias voltage: $U_b\approx-100$ V (strong (111) texture) and $U_b\approx 0$ (polycrystalline films with weak (111) texture). The microcrystalline structure of the films was studied by X-ray diffraction, scanning electron and probe microscopy. The magnetic parameters $4\pi M$ and $\Delta H$ were measured by the FMR technique ($9.9$ GHz). The hysteresis loops and the coercivity field Hc were measured using the vibrating sample magnetometer technique. All measurements were carried out at room temperature with the magnetic field applied in the film plane. The magnetic domain structure was investigated using the magnetic force microscopy. Conclusion: It is shown that the thickness dependencies of $4\pi M(d)$ and $\Delta H(d)$ for Ni(200) films and Ni(111) films with strong and weak (111) texture coincide with the accuracy $10\%$, while the $H_c (d)$ dependencies are different. For polycrystalline NiFe films with weak (111) texture ($U_b\approx 0$) at the critical thickness $d_{cr}\approx 120$ nm the hysteresis loops change from rectangular to “overcritical” and the $H_c$ values increase from $H_c\leq 2$ Oe at $d < d_{cr}$ to $H_c > 40$ Oe for the thicknesses $d > d_{cr}$. For NiFe(111) films with strong (111) texture ($U_b\approx -100$ V) and NiFe(200) the hysteresis loops remain rectangular in the thickness range $d\approx 20$–$370$ nm, $H_c$ values coincide with the accuracy $5\%$ and tend to decrease from $H_c\approx 2.5$–$3$ Oe to $H_c\approx 1.5$–$2$ Oe with increasing thickness. The behavior of the $4\pi M(d)$, $\Delta H(d)$ and $H_c (d)$ dependencies is related to the microcrystalline structure (texture, grain size) of the NiFe films.