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In this paper, we present an experimental study of $\text{L1}_0$-FePt granular films with crystalline/amorphous boron nitride (BN) grain boundary materials for heat assisted magnetic recording (HAMR). It is found that an adequate RF substrate bias yields the formation of hexagonal boron nitride (h-BN) nanosheets in grain boundaries, facilitating the columnar growth of FePt grains during sputtering at high temperatures. The h-BN monolayers conform to the side surfaces of columnar FePt grains, completely encircling individual FePt grains. The resulting core-shell FePt/h-BN nanostructures appear to be highly promising for HAMR application. The high thermal stability of h-BN grain boundaries allows the deposition temperature to be as high as 800oC such that high order parameters of FePt $\text{L1}_0$ phase have been obtained. For the fabricated FePt/h-BN thin film, excellent granular microstructure with FePt grains of 6.5nm in diameter and 11.5nm in height has been achieved along with good magnetic hysteresis properties., Manuscript: 16 pages, 6 figures attached after references. Supplementary information: page 23-27, 4 figures

A systematic investigation has been performed to optimize the microstructure of $\mathrm{L1_0-FePt-SiO_x}$ granular thin film as recording media for heat-assisted magnetic recording. The FePt-BN nucleation layer, which is stable even at $700^\circ \text{C}$, is used to control the grain sizes and microstructure during high-temperature processing. The study finds that films of high-aspect-ratio FePt grains with well-formed silicon oxide (SiOx) grain boundaries require the grading of the deposition temperature during film growth as well as the grading of the silicon oxide concentration. Well-isolated columnar grains of $\mathrm{L1_0-FePt}$ with an average height greater than 11 nm and diameters less than 7 nm have been achieved. Transmission electron microscopy (TEM) analysis of the microstructures of samples produced under a variety of non-optimal conditions is presented to show how the microstructure of the films depends on each of the sputtering parameters., 17 pages, 7 figures, first published in joint MMM-intermag 2022

Grain-to-grain Curie temperature (Tc) variation in the media reduces signal-to-noise ratio due to its contribution in transition jitter noise, especially when average grain size is pushing down to increase the area storage capacity. A thermally insulating magnetic grain boundary may suppress such grain-to-grain Tc variation, especially at small grain size. Here we present an experimental study on the effect of adding thermally-insulating magnetic oxide, in particular BaFexOy, as part of the grain boundary materials in granular FePt-C HAMR media. It is found that the BaFexOy is chemically inert to FePt and the chemical ordering of FePt-BaFexOy-C media are similar to that of FePt-C meida. By tuning the volume fraction of BaFexOy and C, well-separated FePt grains (average grain size = 6.8 nm) surrounded by BaFexOy shell with perpendicular Hc above 35 kOe can be obtained. Transmission electron microscopy study with chemical analysis shows that the magnetic oxide appears to be crystalline and surround the FePt grains with immediate full enclosure. Magnetic measurements indicate an effective increase of magnetic grain size at temperatures below FePt Curie temperature. Pulsed laser pump-probe measurement indicates a measurable reduction of Curie temperature variation for the FePt-BaFexOy-C media with carefully comparison with the reference FePt-C media.

We report the structure, magnetic property and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to exist in the L21 structure with considerable amount of DO3 disorder. Thermal analysis result indicated the Curie temperature is about 711K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 {plus/minus}0.1 was deduced using point contact Andreev reflection (PCAR) measurements. Half-metallic trend in the resistivity has also been observed in the temperature range of 5 K to 300 K. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications., 14 pages, 6 figures, regular article