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

Abstract

The effect of melting point (Tm) of various grain boundary materials (GBMs) on the magnetic properties and nanostructure of FePt granular films was investigated. According to the analysis for the granular films with a constant GBM volume of 30 vol% deposited at a high substrate temperature, the saturation magnetization, Ms, had a strong correlation with Tm. We newly proposed a degree of order evaluation from in-plane X-ray diffraction from the L10 FePt (110) and (220) planes. As the results, neither the degree of order nor the grain diameter had any significant correlation with the Tm of GBM. Based on these analyzes, it was found that an increase of the grain diameter increases the degree of order, which results in enhancement of the coercivity of the FePt granular films. And it was clarified that Ms strongly depends on the degree of phase separation related to the melting point of GBM.

Magnetic properties and nanostructure of FePt-TiN granular films deposited with N2 gas addition for heat assisted magnetic recording media

“…The granular films show almost a constant value of ɑ of around 3.89 Å, even though N 2 gas flow ratio is varied from 0% to 5%. film , K u⊥ , and H k of complete separation calculated from magnetic parameters of FePt films described in the previous results, 22) assuming 70 vol% FePt and 30 vol% GBMs are completely separated, where there is no element decomposes from the GBMs and dissolves into the FePt magnetic grains. Meanwhile, significant change in c can be observed.…”

“…Figure 3 shows dependence of (a) M s film , (b) K u⊥ , and (c) H k on N 2 gas flow ratio for FePt-TiN granular films. Dotted lines in each graph represent the values of M s film , K u⊥ , and H k of complete separation calculated from magnetic parameters of FePt films described in the previous results, 22) assuming 70 vol% FePt and 30 vol% GBMs are completely separated, where there is no element decomposes from the GBMs and dissolves into the FePt magnetic grains. At N 2 gas flow ratio of around 3%, M s film , K u⊥ , and H k, reaches the maximum values of around 630 emu cm −3 , 1.2 × 10 7 erg cm −3 , and 39 kOe, respectively.…”

“…1) To put HAMR media into practice, there are still a lot of challenges, such as the realization of a granular structure with fine columnar magnetic grains, high caxis orientation, and high degree of order. In order to achieve these requirements, many studies of adding grain boundary materials (GBMs), such as C, 2,3) BN, 4,5) TiN, 6) Si 3 N 4 , 7) AlN, 8) TaN, 9) MnO, 10) HfO 2 , 10) MgO, 11,12) TiO 2 , 13) Ta 2 O 5 , 14) GeO 2 , 15) Al 2 O 3 , 16) Nb 2 O 5 , 17) WO 3 , 17) ZrO 2 , 17,18) Cr 2 O 3 , 19) SiO 2 , 20,21) and B 2 O 3 22) into the FePt sputtered thin films to separate the magnetic grains and promote the exchange decoupling have been conducted. In our study of granular films with various GBMs, we have found that saturation magnetization (M s film ) of the granular film depends on the melting point of the GBMs, which means that M s film of the granular film shows the degree of separation between metal magnetic grains and amorphous GBM.…”

“…In our study of granular films with various GBMs, we have found that saturation magnetization (M s film ) of the granular film depends on the melting point of the GBMs, which means that M s film of the granular film shows the degree of separation between metal magnetic grains and amorphous GBM. 22) Concerning the fabrication of the granular films, oxide or nitride in the GBM is decomposed during sputtering to be metal and oxygen or nitrogen gas that induces the oxygen and nitrogen deficiency in the granular film. Therefore, the addition of oxygen or nitrogen gas during the deposition is one of the methods to compensate the deficiency where the stoichiometry of the GBMs will depend on the metal element of the GBMs due to the difference in bonding energy between the metal element and oxygen or nitrogen.…”

Ejection of boron from L10 phase for sputtered FePt-BN granular films by post-annealing

“…According to our previous report, saturation magnetization (M s ) of the granular film depends on the melting point of the GBMs. 11) Additionally, M s of the granular film shows the degree of separation between metal magnetic grains and GBM. Oxide or nitride may be decomposed to be oxygen or nitrogen gas during sputtering, which induces the oxygen or nitrogen deficiency in a granular film.…”