Masaaki Futamoto

Compositional and temperature dependence of basic magnetic properties of CoCr-alloy thin films

Compositional and temperature dependencies of saturation magnetization (M/sub s/) and uniaxial magnetocrystalline anisotropy (K/sub u/) are determined using single crystal CoCr-alloy thin films. Temperature dependencies of M/sub s/ and K/sub u/ are stronger with increasing Cr content. M/sub s/(OK) and Curie temperature (T/sub c/) decrease linearly with increasing Cr content in a Co-Cr-X (X=Ta, Pt) system. M/sub s/(OK) and T/sub c/ become zero at the Cr concentration of 33 at.%, Co-Cr-Pt specimens have higher T/sub c/ and higher K/sub u/ than those of Co-Cr-Ta specimens with similar Cr concentration. The magnetic properties of polycrystalline medium are confirmed to depend strongly on those of Co-rich core crystalline grains in Cr segregated microstructure.

Damping constants of Co-Cr-Ta and Co-Cr-Pt thin films

Gilberts damping constants, α , of Co-Cr-Ta and Co-Cr-Pt thin films are determined by Q-band FMR analysis using single crystal magnetic thin films epitaxialIy grown on MgO(110) substrates. α is calculated from the resonance width of the FMR spectrum. α of Co77Cr19Ta4 is found to increase from 0.016 to 0.028 as magnetic layer thickness increases from 25 to 240 nm. α also increases from 0.009 to 0.019 when the Cr concentration in the 60 nm thick Co96-x CrxTa4 magnetic layer is increased from 8 to 19 at.%. The 25 nm thick Co81Cr15Pt4, film has a 2.5 times larger α value (0.038) than the Co81Cr15Ta4 film (α = 0.014) with the same thickness.

Epitaxial Growth of Co/Cr Bilayer Films on MgO Single Crystal Substrates

Co/Cr bilayer films have been epitaxially grown on MgO (100) and (110) substrates. The Cr (100) and the Co (110) planes are parallel to the MgO (100) substrate plane. The Co layer has a bicrystalline structure which consists of two types of domains with their c-axes lying in-plane and perpendicular to each other. The Cr (211) and the Co (100) planes are parallel to the MgO (110) substrate plane, and a single-crystalline Co layer is obtained with an in-plane c-axis consisting of slightly misoriented subgrains. Both films show azimuthal magnetic anisotropy in the film plane.

Development Of High Resolution And Low Noise Single-layered Perpendicular Recording Meidia For High Density Recording

Single-layered perpendicular recording media with high resolution and low noise characteristics, which can be used for 10 Gb/in/sup 2/ level magnetic recording, have been developed. Noise characteristics of highly oriented CoCr/sub 19/Pt/sub 10/ media are improved, by employing CoCr/sub 35//TiCr/sub 10/ dual-underlayer, by reducing magnetic crystal grain diameter, and by adding Ta to the magnetic layer. A linear recording density resolution (D/sub 50/) value of 260 kFCI and a S/sub 0//N ratio of 36 dB are confirmed for the low noise 50-nm-thick CoCr/sub 19/Pt/sub 10/Ta/sub 2/ dual-underlayer medium using a flying MR head at magnetic spacing of 40 nm.

Crystallographic Properties of LaB6 Formed in Molten Aluminium

By cooling slowly a homogeneous solution of La, B and Al from about 1200°C, single crystals of lanthanum hexaboride (LaB6) were precipitated, and their lattice constant, purity and growh-orientations were investigated. The products are needle-like crystals with a rectangular cross section, thin plate-like crystals and cubical crystals. The LaB6 crystal has the lattice constant 4.1564A and contains impurities of less than 0.01 wt%. More needle-like crystals with [110] growth direction tend to be formed than any crystals with other shapes. For the typical needle-like crystals, the crystal thickness depends on the cooling rate. The average size is 0.1 to 0.5 mm square in cross section and about 5 mm in length.

Microstructures of Co/Cr Bilayer Films Epitaxially Grown on MgO Single-Crystal Substrates

Microstructures of Co/Cr bilayer films epitaxially grown on MgO (100) and (110) single-crystal substrates have been studied by high-resolution transmission electron microscopy. The bicrystalline Co layer formed on the MgO (100) substrate contains a number of (0001) stacking faults. The single-crystal Co layer formed on the MgO (110) substrate consists of slightly misoriented subgrains, grown on (211)-oriented Cr domains. Dislocations and lattice strain are observed at the Cr/MgO (110) interface. The misorientations and the defects are thought to be introduced to accommodate the large lattice mismatch of about -16% in the MgO [10] direction at the Cr/MgO (110) interface.

Noise characteristics of double-layered perpendicular media using novel soft magnetic underlayer materials

The read/write characteristics of perpendicular media with different soft magnetic underlayer (SMU) materials (Co-Nb-Zr, Co-Ta-Zr, Fe-Ta-C, and Fe-Al-Si), and identical recording layers were investigated using a spin-stand and a merged-type MR head. It was observed that there are strong correlations between the SMU materials and noise characteristics, and found that Co-Ta-Zr and Fe-Ta-C underlayers yield the lowest noise when combined with a Co-Cr-Pt-Ta magnetic recording layer. An advanced medium, made based on those findings, was tested and a maximum D/sub 50/ of 275 kFCl was observed by using a single pole-type writer and a GMR reader with a shield gap length of 80 nm.

Microstructure of CoCr Thin Films Prepared by Sputtering

The microstructure and the growth process of sputter deposited CoCr thin films are studied by transmission electron microscopy (TEM). The columnar structure of c-axis oriented CoCr grains is well established at a greater film thickness of about 100 nm. The cross-sectional TEM clearly shows the detailed structure of the initial growth layer, where the c-axis oriented grains are growing in size with increasing distance from the substrate surface. The necessity of controlling the nucleation of CoCr crystal grains at an early stage of film growth is stressed to further improve the c-axis orientation of the film.

Structure and Magnetic Properties of Co Epitaxial Thin Films Grown on MgO Single-Crystal Substrates

Co epitaxial thin films were prepared on single-crystal MgO substrates of (100), (110), and (111) planes heated at 300degC by ultra high vacuum molecular beam epitaxy. The film crystal structure varies depending on the substrate orientation. On MgO(100) substrate, a Co(112macr0) epitaxial bi-crystalline film with an hcp structure is obtained. A Co(110) single-crystal film with an fcc structure is formed on MgO(110) substrate, whereas a Co(0001) single-crystal film with an hcp structure is grown on MgO(111) substrate. Co film growth on MgO substrates follows the Volmer-Weber mode. The in-plane magnetization properties reflect the magnetocrystalline anisotropy of bulk hcp-Co or fcc-Co crystal. The Gilberts damping constants of these 40-nm-thick epitaxial Co films are determined.

Epitaxial growth of hcp/fcc Co bilayer films on Al2O3(0001) substrates

Co magnetic bilayer films with different stacking structures of fcc/hcp and hcp/fcc were successfully prepared on Al2O3(0001) substrates employing Au and Cu underlayers. The structure and the magnetic properties of these bilayer films were investigated. The crystal structure and the strain of Co layers are influenced by the underlayer. Q-band ferromagnetic resonance analysis has shown that the Co bilayer films consist magnetically of fcc and hcp phases. It has been shown possible to prepare hcp/fcc Co epitaxial magnetic bilayer films that can be used for patterned media applications.