Microstructure and magnetic properties of FePt-(C,SiO2) granular films deposited on MgO, MgTiO, and MgTiON underlayers

Sepehri-Amin, H.; Nagano, Miho; Seki, T.; Ho, H. Y.; Tripathy, D.; Pirzada, S.; Srinivasan, Kumar; Yuan, Hua; Dorsey, Paul; Ajan, Antony; Hono, K.

doi:10.1016/j.scriptamat.2018.07.025

Cited by 14 publications

(5 citation statements)

References 14 publications

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“…Many elements, for example, silver (Ag), copper (Cu), etc., have been doped to lower the L10 FePt ordering temperature and Curie temperature, which influenced the process deposition temperature and the laser writing (heat) power during thin-film engineering [ 9 , 10 , 11 ]. In addition, the structure requirement for perpendicular magnetic anisotropy tuned the surface energy and lattice misfit strain between the FePt and MgO-based underlayer [ 12 , 13 , 14 , 15 , 16 ] and CrRu seed layers [ 14 , 17 , 18 ], and sputtered the FePt film with (00L) orientation. In addition, to obtain a uniform granular structure and columnar grains to avoid noise and increase the signal-to-noise ratio, multiple segregants are required and Ag, carbon (C), and boron nitride (BN) are typical grain boundary materials for perpendicular FePt media [ 5 , 6 , 19 ].…”

Section: Introductionmentioning

confidence: 99%

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films

et al. 2023

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A sputtered FePt(BN, Re, C) film, here boron nitride (BN), was compared to a reference sample FePt(BN, Ag, C). Intrinsically, these films illustrate a high anisotropy field (Hk) and perpendicular magnetocrystalline anisotropy (Ku),although the reference sample shows a higher value (Hk = 69.5 kOe, Ku = 1.74 × 107 erg/cm3) than the FePt(BN, Re, C) film (Hk = 66.9 kOe, Ku = 1.46 × 107 erg/cm3). However, the small difference in the anisotropy constant (K2/K1) ratio presents a close tendency in the angular dependence of the switching field. Extrinsically, the out-of-plane coercivity for the reference sample is 32 kOe, which is also higher than the FePt(BN, Re, C) film (Hc = 27 kOe), and both films present lower remanence (Mr(parallel)/Mr(perpendicular) = 0.08~0.12), that is, the index for perpendicular magnetic anisotropy. The higher perpendicular magnetization for both films was due to highly (001) textured FePt films, which was also evidenced by the tight rocking width of 4.1°/3.0° for (001)/(002) X-ray diffraction peaks, respectively, and high-enough ordering degree. The reference sample was measured to have a higher ordering degree (S = 0.84) than FePt(BN, Re, C) (S = 0.63). As a result, the Ag segregant shows stronger ability to promote the ordering of the FePt film; however, the FePt(BN, Re, C) film still has comparable magnetic properties without Ag doping. From the surface and elemental composition analysis, the metallic Re atoms found in the FePt lattice result in a strong spin–orbital coupling between transition metal Fe (3d electron) and heavy metals (Re, Pt) (5d electron) and we conducted high magnetocrystalline anisotropy (Ku). Above is the explanation that the lower-ordered FePt(BN, Re, C) film still has high-enough Ku and out-of-plane Hc. Regarding the microstructure, both the reference sample and FePt(BN, Re, C) show granular structure and columnar grains, and the respective average grain size and distributions are 6.60 nm (12.5%) and 11.2 nm (15.9%). The average widths of the grain boundaries and the aspect ratio of the columnar grain height are 2.05 nm, 1.00 nm, 2.35 nm, and 1.70 nm, respectively.

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Section: Introductionmentioning

confidence: 99%

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films

et al. 2023

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“…The intermediate layer has suitable lattice mismatch and provides a template for the growth of c-axis or (001) textured FePt film. The MgO-related materials, for example, using transition metal ion or nitride such as (Ti, Cu, Co, Ni, TiN) to replace part of the Mg 2+ to improve the MgO target conductivity, have been discussed [ 9 , 10 , 11 , 12 ]. The surface energy and lattice misfit strain can be tuned between FePt and the intermediate layer and, finally, the FePt (00L) film can be sputtered on a (002) textured MgO-based intermediate layer using direct current magnetron sputtering.…”

Section: Introductionmentioning

confidence: 99%

Switching Field Distribution in BN/FePtCAg/MgTiON and FePtCAg/MgTiOBN Films

et al. 2022

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BN is the currently required segregant for perpendicular FePt media. We found that BN can be diffused from the MgTiOBN intermediate layer during a high temperature process. The FePtCAg film sputtered on MgTiOBN layers illustrates higher perpendicular magnetocrystalline anisotropy (Ku) (1.43 × 107 erg/cm3) and coercivity (normal to film surface) (17 kOe) at 350 K compared to BN/FePtCAg/MgTiON film. From the microstructure, the FePtCAg film shows the granular structure on the MgTiOBN intermediate layer, but parts of the irregular FePt grains are agglomerated and partially separated in the matrix, with grains size being, on average, 26.7 nm. Cross-sectional imaging showed that the FePt grains have a truncated pyramid shape with a lower wetting angle, which is influenced by the surface energy of MgTiOBN. BN segregation at FePt grains or boundaries is still not clear. Using the electron energy loss spectrum (EELS), we found that part of the BN atoms were clearly observed in the FePt lattice and iron-boride oxide was indexed in the x-ray photoelectron spectroscopy (XPS) spectra. To determine the effects of BN segregant (from capping layer or intermediate layer) on the magnetic switching behavior of FePtCAg film, the intrinsic-(ΔHint = 6.17 kOe, 6.54 kOe) and extrinsic- (ΔHext = 0.80 kOe, 0.39 kOe) switching field distribution (SFD) were measured by plotting saturated major- and unsaturated minor- hysteresis loops to evaluate the crystal orientation and microstructure (grains volume and distribution) for BN/FePtCAg/MgTiON and FePtCAg/MgTiOBN films, respectively. The main contribution of intrinsic SFD is the c-axis misalignment for the BN/FePt/MgTiON sample; however, the dispersed magnetic anisotropy has a higher input to intrinsic SFD for FePtCAg/MgTiOBN/CrRu film.

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“…size. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] However, in the case of magnetic recording media, the high grain density will be essential to obtain high signal to noise ratio in high areal density. As mentioned in the introduction even if grain coalescence is suppressed, the required grain density of 24 T in −2 for 4 Tbit in −2 cannot be achieved in our sputtering process.…”

Section: Introductionmentioning

confidence: 99%

Grain density control in FePt granular films for heat-assisted magnetic recording media

Suzuki

Takahashi

2022

Jpn. J. Appl. Phys.

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To realize high areal density hard disk drives (HDDs) larger than 4 Tbit/in2, ultrafine FePt grains of less than 5 nm and grain density larger than 24 T/in2 are required. Although there have been many investigations to reduce the grain size of FePt, there are few reports on the control of grain density. To increase the grain density, we focused on three aspects of the surface morphology and grain density: nucleation sites on the substrate surface, surface free energy, and lattice mismatch. We achieved 14 T/in2 by maximizing the number of nucleation sites in the FePt-C granular film and found that the surface free energy and lattice mismatch are crucial parameters for controlling the grain density.

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Microstructure and magnetic properties of FePt-(C,SiO2) granular films deposited on MgO, MgTiO, and MgTiON underlayers

Cited by 14 publications

References 14 publications

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films

Switching Field Distribution in BN/FePtCAg/MgTiON and FePtCAg/MgTiOBN Films

Grain density control in FePt granular films for heat-assisted magnetic recording media

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