High-frequency magnetic properties in metal–nonmetal granular films (invited)

Abstract

The structure and properties of Co–N and Co–O based films, prepared by rf magnetron reactive sputtering using nitrogen or oxygen and argon gases, have been studied. Transmission electron microscopy (TEM) observation reveals that each Co–(Al or Si)–(N or O) film is a typical film with granular structure, with grain size less than 5 nm. It is found by micro-focused energy-dispersive x-ray and electron energy loss spectroscopy analysis that the grains are mainly composed of Co and the intergranular regions are ceramics of N or O. In Co–N based films, soft magnetic properties are found in both Si and Al containing films over a wide range of film preparation conditions and compositions. Only the films with Al show soft magnetic properties in Co–O based films, which have ρ of 500–1000 μΩ cm, Hk of about 80 Oe and Bs of about 10 kG. By adding about 10 at. % Pd, the soft magnetic properties and Hk of Co–O based films are significantly improved, with Hk more than 180 Oe. These films exhibit a remarkable constant frequency response of the permeability up to around 500 MHz, which is approximately explained by the Landau–Lifshitz formula.

Enhancement of low-field magneto-dielectric response in two-dimensional Co/AlF granular films

“…For reported FeCo-MgF granular films, 11 the MD ratio is considerably small (De 0 /e 0 ¼ 0.1%) even under a magnetic field of H ¼ 1000 Oe. Indeed, granular nanocomposites offer variables to easily adjust the functionality, including, e.g., ferromagnetic 14 and superparamagnetic properties, 15 depending on the granule concentration. However, it is difficult to alter the granular distribution and interactions in a homogeneous structure, which are critical for controlling or enhancing a material's multi-functionality.…”

Magnetic properties and thermal stability of Co/HfN multilayer films for high-frequency application

“…[1][2][3] The granular films with nanometer-sized ferromagnetic granules dispersed in an insulating matrix display a variety of multifunctional properties, e.g., magnetoresistance 4 and magnetoelectric 5 and soft ferromagnetic effect. 6 Theoretically, the magnetic softness achieved by reduced magnetocrystalline anisotropy can be explained by the random anisotropy model. 7 However, sputtered granular films tend to exhibit perpendicular magnetic anisotropy (PMA) because of the growth-induced columnar structure of the magnetic granules.…”

Properties and Structure of High Frequency Soft Magnetic Nano-composite Films

“…We have so far been extensively studying nano-granular, soft magnetic (named simply "NGSM", hereafter) films as high frequency materials useful at the GHz range. Such a film has been successfully synthesized by forming Co based, metal-insulator type, nano-granular magnetic thin films [4]. NGSM films were found to satisfy these properties with (Fe, Co, Ni)-(Al, Si, Zr, Mg, RE)-(oxide or nitride) and (Fe, Co)-(Al, Mg)-fluoride systems (RE: rare earth elements) [5].…”