B₂O₃: Grain boundary material for high-K_u CoPt–oxide granular media with low degree of intergranular exchange coupling

Abstract

The magnetic properties and structures of Co80Pt20–30 vol % oxide (ZrO2, Cr2O3, Y2O3, Al2O3, MnO, TiO2, WO2, SiO2, Mn3O4, WO3, Co3O4, MoO3, and B2O3) granular media deposited at room temperature were investigated. As a result, the following were found. 1) By employing oxides with low melting point temperatures as the granular media, magnetic grains with high saturation magnetization ( ) and perpendicular magnetic anisotropy ( ) are obtained; the increases in and are due to the promotion of the columnar growth of magnetic grains and phase separation or two-phase precipitation between magnetic grains and oxides. 2) The increase in the of the granular media followed by the decrease in the melting point of oxides is due to the reduction in the amount of stacking faults. 3) Among these granular media, the CoPt–B2O3 granular medium has the highest coercivity (H c) and ratio of H c to the magnetic anisotropy field ( ) of 8.0 kOe and 0.4, with and of 1115 emu/cm3 and 1.1 × 107 erg/cm3, respectively. 4) The CoPt–B2O3 granular medium has well-isolated and columnar growth magnetic grains with an average grain size of 6.5 nm.

Reduction of intergranular exchange coupling and grain size for high Ku CoPt-based granular media: Metal-oxide buffer layer and multiple oxide boundary materials

“…To realize these requirements, the segregation of oxides material into the grains boundaries and the promotion of phase separation between the oxide and metal material are essential. Generally, for the grain boundary materials, oxides material which do not dissolve into the CoPt metal, such as SiO 2 , 3 8,9 Furthermore, by mixing low T m B 2 O 3 with high T m oxides, media with small magnetic grain size can be obtained. 10 It is also shown that the introduction of a buffer layer (BL) underneath the granular media has a great impact on promoting the intergranular exchange decoupling of the media.…”

Ultrafine, Dual-Phase, Cation-Deficient PrBa0.8Ca0.2Co2O5+δ Air Electrode for Efficient Solid Oxide Cells

“…One reason for the exsolution of Co and formation of Co 3 O 4 is that the Co cations near the surface of PBCC grains are strongly attracted by the surface oxygen vacancies, whose concentration increases under polarization conditions. , In addition, the limited initial physical contact between the electrode and electrolyte can result in local heating due to the release of Joule heat as oxygen ions transport at the electrode–electrolyte interfaces during polarization, which further increases the concentration of surface oxygen vacancies (Figure a). The in situ -formed Co 3 O 4 phase with a relatively low melting temperature , probably serves as a bridging layer to firmly adhere the PBCC-d750 electrode to the GDC barrier layer (Figure b). The promotional effect of this bridging layer is similar to the enhancement of interfacial contact by diffusion of in situ generated molten carbonate from the cathode to the electrolyte in the case of carbonate-superstructured SOCs …”

Effects of utilizing a granular nucleation layer on magnetic properties and microstructure of CoPt–B2O3 granular medium

“…Previously, we found that a medium with magnetic grains of high magnetocrystalline anisotropy (K u ) was successfully realized when a lowmelting-point oxide, B 2 O 3 , was used as the grain boundary material. 9) However, the grain diameter of the CoPt-B 2 O 3 granular medium is larger than those of granular media with multiple oxides. 10) One of the methods of reducing the grain diameter of the granular medium is to insert a nucleation layer with small grain diameter.…”