Magnetic Properties and Columnar Structure for CoPt Alloy Granular Media With Grain Boundary Oxides of Various Melting Points

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.…”

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

“…Results and discussion 3.1 Microstructure of CoPt-B 2 O 3 granular medium with NL In our previous paper, we reported that the columnar grain growth of the CoPt-oxide granular layer with a thickness of 16 nm deteriorated when an oxide with high T m was utilized. 13) To investigate the columnar grain growth of the CoPt-B 2 O 3 granular layer with NL deposited underneath, the cross-sectional structure of the granular medium was observed. Figure 1 shows the cross-sectional TEM images of CoPt-B 2 O 3 granular medium deposited (a) without and with an NL consisting of the typical oxides (b) WO 3 , (c) TiO 2 , and (d) ZrO 2 .…”

“…This result indicates that the employment of an NL with appropriate thickness is considerably effective for increasing H c and the NL thickness at which each oxide shows the peak of H c decreases when an oxide with higher T m is employed. The possible origin of H c at various d NL values in the granular medium is the existence of an inhomogeneous structure in the medium 13,[18][19][20] or the noncoherent magnetic reversal mode [21][22][23] or the change in the degree of thermal stability 24,25) or intergranular exchange coupling. [26][27][28][29] In accordance with the result in the previous section, each magnetic grain grows columnarly with c-plane sheet texture orientation such that the existence of an inhomogeneous structure in the medium and the noncoherent magnetic reversal mode are not the primary issues for the granular medium.…”

“…11,12) Recently, we reported that a granular medium with a single high-melting-point oxide showed a smaller grain diameter than the granular medium with a low-melting-point oxide. 13) Taking advantage of this feature, to realize a granular medium with high K u and small grain diameter, we investigated the CoPt-B 2 O 3 granular medium deposited on nucleation layers (NLs) consisting of CoPt-oxide granular layers of various melting points. In this paper, we will discuss the magnetic properties and microstructure of those media with dual granular layers.…”

Effect of melting point of grain boundary material on nanostructure and magnetic properties of L10 type FePt granular media

“…The critical thickness of homogeneous granular structure along the thickness direction (d cri ), the amount of stacking faults (P fcc ), and K u are all strongly dependent on the melting point (T m ) of GBM. 4,5) GBMs with low T m result in good phase separation between the magnetic grains and the GBM in granular media, which leads to an increase of d cri and K u , while P fcc decreases. For heat-assisted magnetic recording (HAMR) as a next-generation technology, L1 0 type FePt based granular media deposited on a flat MgO underlayer at a high substrate temperature is a promising candidate.…”