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To apply Nd–Fe–B thin films for mass-produced heat-assisted magnetic recording media, we investigated the high-rate sputtering conditions required to obtain c-axis textured Nd2Fe14B thin films and analyzed the growth mechanism. Magnetization curves indicated that higher substrate temperatures and sputtering rates resulted in a higher degree of perpendicular magnetic anisotropy; a Nd–Fe–B layer deposited at a substrate temperature (Tsub_0) of 600 °C and a sputtering rate (Rsp) of 2.6 nm/s had the easy axis perpendicular to the film plane. The dependence of the magnetic properties on the sputtering rate was due to a decrease in the substrate temperature during sputtering; there was a threshold for obtaining a high squareness ratio. X-ray diffraction analysis and transmission electron microscopy (TEM) images showed that the c-axis textured Nd2Fe14B crystal phase was formed in the Nd–Fe–B layer deposited at Tsub_0 = 600 °C and Rsp = 2.6 nm/s, which resulted in the highly perpendicular magnetic anisotropy. In addition, the TEM images showed a layer of Nd2Fe14B with no obvious lattice fringes near the interface between the Nd–Fe–B layer and Mo underlayer, while the lattice fringes of the Nd2Fe14B phase were not parallel to this interface but gently curved along the Mo cap layer. We propose that the c-axis orientation was achieved by the rotation of the c plane, which has the lowest surface energy in the Nd2Fe14B phase, toward the vacuum-side surface during sputtering. [ABSTRACT FROM AUTHOR]

Magnetic properties and nanostructure for FePt-30 vol% BN granular films deposited while flowing N2 gas with ratio between 0% and 5% with respect to the total flow of N2 + Ar are investigated. Here is a list of the results: 1) A maximum coercivity ($H_{\mathrm {c}}$) of 18.9 kOe, a saturation magnetization ($M_{\mathrm {s}}$) of 600 emu/cm3, a perpendicular magnetic anisotropy ($K_{\mathrm {u\bot }}$) of $1.7\times 10^{\mathrm {7}}$ erg/cm3, and a magnetic anisotropy field ($H_{\mathrm {k}}$) of 58 kOe, with smaller grain size and higher degree of grain separation are obtained when N2 gas with a ratio of around 2% is added; 2) higher fraction of N2 gas ratio leads to an increase of the amount of magnetic grains with $c$ -axis parallel to the film plane; 3) lattice constant $a$ remains constant, a minimum value of lattice constant $c$ and the ratio $c/a$ are also observed for a N2 ratio of around 2%; 4) there are two phenomena observed in nanostructure and magnetic properties defined by the N2 ratio. For N2 ratios under 2%, changes in the $c/a$ ratio, the degree of order, and the agglomeration suppression of grains enhance $M_{\mathrm {s}}$ , $K_{\mathrm {u\bot }}$ , and $H_{\mathrm {k}}$. This indicates that the segregation of B into grain boundaries as the result of the N2 addition. For N2 ratios over 2%, the change of tetragonal into cubic FePt magnetic grains, the reduction of the degree of order, and the decrease of $M_{\mathrm {s}}$ and $K_{\mathrm {u\bot }}$ suggest that excess nitrogen dissolves into the FePt magnetic grains; and 5) another consequence of the 2% N2 ratio is the enhancement of the magnetic grain decoupling along with the increase of $H_{\mathrm {k}}$ , this results in the maximization of $H_{\mathrm {c}}$. [ABSTRACT FROM AUTHOR]

A sputtered tape that uses a CoPt-based granular recording layer was developed for practical application in the next generation of large-capacity magnetic tapes. 1) First, disk media were prepared by depositing films onto glass substrates using an inline disk sputter machine in which the substrates were stationary facing the target, and the ability to control the crystalline orientation, the magnetic isolation, and the magnetic anisotropy of the recording layer, which are the important functions of the underlayer, was investigated. As a result, it was found that the medium with Co60Cr40 (45 nm)/Co60Cr40-15 vol.% TiO2 (5 nm) as the underlayer has the same properties as the medium with the Ru underlayer. 2) Next, a sputtered magnetic tape with Co60Cr40 (25 nm)/Co60Cr40-SiO2 (25 nm) as the underlayer deposited on a polymer film was prepared using a roll-to-roll sputtering machine. The ability to control the crystalline orientation and magnetic isolation of the magnetic recording layer was evaluated, and from the results it was found that a magnetic film with a granular structure was formed on the sputtered magnetic tape in which the $c$ -axis of the magnetic crystal grains is oriented in the direction perpendicular to the film and the magnetic crystal grains are separated by the SiO2 amorphous phase. 3) Furthermore, when the recording properties of the sputtered magnetic tape with a Co60Cr40 (25 nm)/Co60Cr40-SiO2 (25 nm) underlayer were compared with those of a magnetic tape for a linear tape-open (LTO) format eighth-generation tape cartridge (LTO 8), it was confirmed that the broadband signal-to-noise ratio of the sputtered tape with a Co60Cr40/Co60Cr40-SiO2 underlayer is 4.2 dB higher than that of the LTO 8 tape at a linear density of 300 kfci. [ABSTRACT FROM AUTHOR]

Perpendicular 90 kOe torquemetry analysis of magnetic anisotropy ($K_{\mathrm {u\bot }}^{\mathrm {exp}}$) for L10-typed FePt granular media with various grain boundary materials (GBMs) was conducted. According to the analysis for granular films with a constant GBM volume of 30 vol% deposited at a high substrate temperature, $K_{\mathrm {u\bot }}^{\mathrm {exp}}$ was not dependent on the saturated torque coefficient of fourfold components ($L_{4\theta }^{\mathrm {sat}}$) but was dependent on that of twofold components ($L_{2\theta }^{\mathrm {sat}}$) originating from magnetic grains with $c$ -axes normal to the film plane. Furthermore, $L_{4\theta }^{\mathrm {sat}}$ mainly originated from FePt grains with $c$ -axes parallel to the film plane. $K_{\mathrm {u\bot }}^{\mathrm {exp}}$ also had a strong correlation with grain diameter ($GD$) and degree of order ($S_{\mathrm {in}}$). On the other hand, $K_{\mathrm {u\bot }}^{\mathrm {exp}}$ had no significant correlation with the melting point ($T_{m}$) of the GBM, which indicates that the dominant factor affecting $K_{\mathrm {u\bot }}^{\mathrm {exp}}$ was not phase separation. Based on these evaluations, an increase of $GD$ caused an increase of $S_{\mathrm {in}}$ , regardless of the GBMs, which resulted in enhancement of $K_{\mathrm {u\bot }}^{\mathrm {exp}}$ for the FePt granular films. [ABSTRACT FROM AUTHOR]

Investigation of magnetic properties and nanostructure for full granular media with CoPt−Gd2O3 granular cap layers (CLs) of various Gd2O3 content were conducted. Media with low surface roughness of 0.19 nm is maintained even though Gd2O3 content is reduced from 30 to 5 vol%, which is lower than that of media with CoPtCrB continuous CL. The result is supported by surface morphology observed by transmission electron microscopy. According to cross section element analysis, homogeneous nanostructure in the thickness direction with one- text on-one columnar growth of magnetic grain is observed. Reduction of Gd2O3 content increases indirect intergranular exchange coupling through CL which results in media with higher nucleation field and lower saturation field than that of media with CoPtCrB continuous CL. Furthermore, at a CL thickness of 6 nm, when Gd2O3 content is reduced from 30 to 15 vol%, switching field distribution is reduced from 0.11 to 0.05. These results suggest that the reduction of Gd2O3 content of the CoPt−Gd2O3 granular CL is effective to reduce the switching field distribution of the full granular media to be lower than that of media with CoPtCrB continuous CL while retaining the extremely smooth media surface. [ABSTRACT FROM AUTHOR]

Investigation of magnetic properties and nanostructure of stacked media with a CoPt-B2O3 granular recording layer (GRL) and granular cap layers (CL) with CoPt and a typical ferromagnetic oxide of rare earth (RE) oxide (RE oxide: Gd2O3, Nd2O3, Sm2O3, and CeO2) are reported. CoPt-RE oxide granular layer shows higher saturation magnetization and magnetic anisotropy than that of CoPtCrB continuous layer. In stacked media with CoPt-Gd2O3 granular CL (9 nm), nucleation field increases from 0.7 to 0.8 kOe and saturation field decreases from 21.5 to 12.5 kOe with comparable values to those of CoPtCrB continuous CL. This indicates that CoPt-RE oxide granular CL is effective to control intergranular exchange coupling. Reduction of coercivity distribution ratio (∆Hc/Hc) from 0.15 to 0.09 which is comparable to that of CoPtCrB continuous CL when CoPt-Gd2O3 granular CL thickness is changed from 4 to 9 nm is observed. This means CoPt-Gd2O3 granular CL is effective to reduce switching field distribution. Furthermore, significant reduction of surface roughness (Ra) for media with CoPt-Gd2O3 granular CL (9 nm) from 0.32 to 0.25 nm is observed. This reveals that CoPt-RE oxide granular CL has a great impact to induce stacked media with flat surface. Based on the cross-section observation by TEM, the media with CoPt-Gd2O3 granular CL shows continuous structure of grain boundaries from the GRL up to the CL and which results in one-on-one growth of magnetic grain with homogeneous columnar structure. Focusing on the surface morphology, media with CoPt-Gd2O3 granular CL shows smoother surface than that of media with CoPtCrB continuous CL which supports the Ra evaluation result. These results indicate that the employment of granular CoPt-RE oxide for CL is not only to reduce switching field distribution but also to flatten surface of the stacked media. [ABSTRACT FROM AUTHOR]

The α′′-Fe16N2 has attracted much interest as a candidate for semi-hard magnetic materials. As reported coercivity of α′′-Fe16N2 nanoparticles so far were not high, it is necessary to improve magnetocrystalline anisotropy of α′′-phase to be used practically. Since theoretical calculation suggests a possibility of the improvement of magnetocrystalline anisotropy by substituting of Fe with Co, we challenged to make α′′-(Fe1-xCox)16N2 nanoparticles by hydrogen reduction of α-(Fe1-xCox)OOH as a starting material changing X from 0 to 0.1. We were able to produce α-(Fe1-xCox) nanoparticles through (Fe0.98Co0.02)OOH, and (Fe0.95Co0.05)OOH and (Fe0.95Co0.05)2O3. Sintering occurred during reduction and crystallite diameter D increased with increasing reduction temperature. α′′-(Fe1-xCox)16N2 phase containing α-(Fe,Co) nanoparticles were obtained only at reduction of 340 °C for 4 h and nitridation of 170 °C for 5 h for X = 0.02. It has been revealed that α′′-(Fe1-xCox)16N2 or α′′-Fe16N2 could be formed below D = 50 nm of α-(Fe,Co) or α-Fe. And containing Co make it more difficult to produce α′′-phase. It can be said that the formation of α′′-(Fe1-xCox)16N2 is subject to a limit of D and Co content. Long time nitridation is only way to increase the formation yield of α′′-(Fe1-xCox)16N. High Hc = 2000 Oe was obtained for α′′-(Fe0.98Co0.02)16N2 by changing nitridation time 10 hours from 5 hours. Further long nitradation is expected to increase in Hc of α′′-(Fe0.98Co0.02)16N2. [ABSTRACT FROM AUTHOR]

Crystal structure and magnetic properties for Co–Pt–Ru alloy films and Co–Pt–Ru–oxide granular films were investigated for material to reduce the lattice mismatch between the magnetic layer and the nuclei control layer of the perpendicular magnetic recording media. The laminate stacking structure of the sample was sub/NiFeCr (20 nm)/Ru (20 nm)/Co–Pt–Ru (20 nm). The amount of stacking faults in the films was evaluated as a probability of occurrence of fcc stacking, Pfcc measured by an in-plane X-ray diffractometry profile. As a result, it was found that: 1) hcp atomic stacking structures of the Co100–xRux alloy films were stable compared with that of Co100–xPtx alloy films for almost all of the additional content x; 2) lattice constant a and c for Co–Pt–Ru ternary alloy film could be controlled between 2.51 to 2.59 Å, and 4.07 to 4.41 Å, as changing the Pt and Ru content with a total amount of 0 to 50 at.%, respectively. And the lattice constant ratio c/a decreased from 1.62 to 1.59 with increasing Ru content more than 20 at.%; 3) Pfcc in the Co–Pt–Ru ternary alloy films was less than 0.5% for the samples with Ru content were more than 20 at.%; 4) uniaxial magnetocrystalline anisotropy Ku could be controlled from 12.6 to 0 106 erg/cm3 by adding Pt and Ru with a total amount of 30 at.% to a Co75Pt25 film; and 5) Co–Pt–Ru–(SiO2) film with the columnar structure was realized for Ar gas pressure of 4 Pa during sputtering. [ABSTRACT FROM AUTHOR]

The effect of topological bumpy surface underlayer on compositionally modulated atomic layer stacking in high uniaxial magnetocrystalline anisotropy ( $K_u$ ) hcp Co80Pt20 film with (00.2) crystallographic texture orientation was investigated. In this paper, the following has been discussed. Concerning preparation of underlayer with various morphologies, an annealing process prior to the deposition of Co80Pt20 film, and introduction of a metal-oxide buffer layer are effective to obtain underlayers with surface roughness ranging from \sim 0.4$ to 2 nm and grain size ranging from \sim 6.7$ to 12.5 nm. To realize a compositionally modulated atomic layer stacking structure, which is confirmed by the high angle annular dark field detector scanning transmission electron microscopy observation, an underlayer with surface roughness less than \sim 1$ nm and/or grain size larger than \sim 8 erg/cm $^3$ , surface roughness reduction to $ \sim 0.5$ nm and grain size increase to $ \sim 12$ nm are needed. [ABSTRACT FROM AUTHOR]

Magnetic properties and microstructure of Co80Pt20-30 vol.% (Al2O3, TiO2, WO3) and Co82.4Pt17.6-27.7 vol.% SiO2 granular films postannealed at various temperatures in a heat-treating furnace were investigated. In this paper, it is found that among these granular films, CoPt-WO3 granular film shows the highest coercivity ( Hc ) because of low intergranular exchange coupling of well-isolated magnetic grains. Furthermore, the Hc is enhanced with postannealing because of the increase of the magnetic anisotropy field ( Hk^{\mathrm {grain}} ) and uniaxial magnetocrystalline anisotropy ( Ku^{\mathrm {grain}} ) of the columnar growth magnetic grains. The increase of Ku^{\mathrm {grain}} for the postannealed granular film primarily originates from the reduction of the stacking faults as well as the lattice constant ratio. [ABSTRACT FROM AUTHOR]

The effect of replacing Co with Fe in disordered CoPtRh alloy films was investigated with the aim to increase the spin magnetic moment. The addition of Fe into a pure Co film produced a Co98Fe2 film with maximum uniaxial magnetocrystalline anisotropy (Ku), because the magnetic moment is increased with the same degree of stacking faults (SFs) induced into the hcp grains as that for a pure Co film. (Co0.98Fe0.02)PtRh films were compared with CoPtRh films with the same Pt and Rh contents, which revealed that: 1) the degree of SFs were increased; 2) the magnetic moment was increased; and 3) Ku was decreased for all compositions in the (Co0.98Fe0.02)PtRh films. In particular, the (Co0.98Fe0.02)PtRh and CoPtRh films with a larger Rh content than Pt have a greater range for increase of the Ku magnitude by enhancement of the magnetic moment with the retention of or further decrease in the degree of SFs. [ABSTRACT FROM AUTHOR]

Field induced magnetic anisotropy in two Fe-based amorphous alloys with different saturation induction levels (1.56 T and 1.64 T) was investigated by varying magnetic field strength and annealing temperature and domain images were taken on these samples. Residual strain was evaluated by measuring coercivities of the materials after stress-relief annealing. These results are discussed, clarifying the difference between the two Fe-based amorphous alloys. [ABSTRACT FROM AUTHOR]