In-plane Anisotropy in Hetero-Amorphous (CoFeB)-SiO₂ Thin Films

Abstract

In order to engineer materials suitable for micromagnetic inductor cores we have fabricated and investigated the properties of granular (CoFeB)-SiO2 amorphous thin films. The deposition method, synchronous triple-rf magnetron sputtering onto rotating substrates, induces anisotropy in the film plane. Here we present magnetic hysteresis loops, resistivity and magnetoresistance measurements of two of these films, with different amount of metallic content. Both films have anisotropic resistivity, which is higher for the film with less metallic content. The low-metallic-content film exhibits typical isotropic giant magnetoresistance (GMR), while the film with higher metallic content shows a mixture of GMR and anisotropic magnetoresistance (AMR). The AMR appears at fields below 500 Oe. We believe that this has not been observed before in amorphous samples. The behaviour of the resistivity versus temperature ρ (T) indicates that the sample with lower metallic content consists of isolated grains while the high-metallic-content sample consists of a percolated network. Experimental ρ (T) data for the low-metallic-content sample fit: to the variable-range hopping model at temperatures lower than 221 K and can be described by excitation of the carriers to the mobility edge at higher temperatures.

The superferromagnetic state in the ensemble of oriented Stoner-Wohlfarth particles: a coercivity due to phase stability

“…Since M r at T b < T < T sf is determined by a spontaneous magnetization of the SF phase, we may assert that the SF state preserves a homogeneous ferromagnetic order during the magnetization reversal, and no SF domains similar to described in [8,11,13] appear in the specimen. At the same time, no homogeneous magnetization of the film appears and demonstrates a decreasing angular dependence H C (ϕ) [17]).…”

“…Granular films (Co 0.25 Fe 0.66 B 0.09 ) 0.6 -(SiO 2 ) 0.4 about 500 nm in thickness were grown by magnetron sputtering [16,17]. The X-ray diffraction studies [17] showed that the granules are amorphous.…”

“…Granular films (Co 0.25 Fe 0.66 B 0.09 ) 0.6 -(SiO 2 ) 0.4 about 500 nm in thickness were grown by magnetron sputtering [16,17]. The X-ray diffraction studies [17] showed that the granules are amorphous. A film reveals the easy-plane anisotropy related to the demagnetization factor of the film as a whole (4πM ef f ∼ = 9500 Gs).…”