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Sm17(Co1−xCux)83 and Er17(Co1−xCux)83 (at. %, x = 0–1) alloy thin films are prepared on Cr(100) single-crystal underlayers at 500 °C by molecular beam epitaxy. The effect of Cu/Co composition on the ordered phase formation is investigated. Sm17(Co1−xCux)83(11 2 ¯ 0) films with hexagonal Sm(Co,Cu)5 (D2d) ordered phase grow epitaxially on the underlayers for all the compositional range of x = 0–1. On the contrary, the structure of Er17(Co1−xCux)83 film varies depending on Cu composition. Amorphous phase is formed in the Er17Co83 (x = 0) film. Er17(Co1−xCux)83(11 2 ¯ 0) epitaxial films with Er(Co,Cu)5 (D2d) ordered phase are obtained for the compositional range of x = 0.25–0.5. With further increasing the x value, the crystallographic phase varies to a phase other than D2d. Partial substitution of the Co sites in ErCo5 structure with Cu atoms and control of the amount of Cu atom are important to stabilize the Er(Co,Cu)5 phase.

Er17(Co1− x Cu x )83 (at. %, $x = 0-1$ ) alloy thin films are prepared at 500 °C by employing Cr(211) underlayers hetero-epitaxially grown on MgO(110) substrates. Crystallographic phase formation is influenced by the Cu/Co composition. Amorphous film is formed for $x = 0$ , whereas epitaxial films are obtained for $x = 0.25-1$ . Cu atom addition into Er–Co film promotes crystallization. The films with $x = 0.25-0.5$ consist of a mixture of Er(Co,Cu)5 $(1\bar {1}00)$ and Er(Co,Cu)5(0001) crystals. The crystallographic orientation relationships are Er(Co,Cu)5 $(1\bar {1}00)[\bar {1}\bar {1}20]~\vert \vert $ Cr(211) $[\bar {1}11], (211)[1\bar {1}\bar {1}]$ and Er(Co,Cu)5 $(0001)[\bar {1}\bar {1}20]~\vert \vert ~\text {Cr}(211)[\bar {1}11], (211)[1\bar {1}\bar {1}]$ . However, with further increasing $x$ value, the crystallographic phase changes to a phase different from Er(Co,Cu)5. Control of the amount of Cu atom is important to stabilize the Er(Co,Cu)5 phase.

FePt alloy films of 2 to 10 nm thicknesses are prepared on (001) single-crystal underlayers of MgO, VN, and VC by employing a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. MgO, VN, and VC crystals are selected as underlayer materials, since the crystals have the same NaCl-type crystal structure and similar lattice constants of about 0.42 nm but different surface energies. The single-crystal underlayers are prepared by RF sputtering on the single-crystal substrates of MgO and SrTiO3 at 600 °C. The influences of underlayer material and FePt film thickness on the $L1_{0}$ ordering degree, the magnetic properties, and the surface morphology are systematically investigated. Epitaxial films involving $L1_{0}$ (001) crystal structure with the $c$ -axis normal to the substrate surface are formed on all the underlayers. As the film thickness decreases, the ratio of out-of-plane to in-plane lattice constant $c/a$ decreases and the ordering degree $S$ increases. Stronger perpendicular magnetic anisotropy is observed for an FePt film with a higher $S$ value. The film thickness trends of $c/a$ , $S$ , and magnetic properties are similar to those for FePt films thicker than 5 nm formed on MgO underlayers. However, when the thickness is decreased to 2 nm, de-wetting of deposited atoms occurs on MgO underlayers during annealing at 600 °C. The surfaces of 2-nm-thick films formed on MgO underlayers are composed of isolated islands. On the contrary, continuous surfaces are realized for the investigated film thickness range of 2–10 nm in the cases of VC and VN underlayers. The surface roughness of FePt film formed on VN underlayer ( $R_{a}$ : 0.1–0.2 nm) is lower than that of film formed on VC underlayer ( $R_{a}$ : 0.1–0.4 nm). This paper shows that the employment of a VN underlayer is effective in the preparation of $L1_{0}$ ordered FePt ultra-thin film with flat surface.

Fe50PtxPd50−x (at%, x=0–50) alloy films of 10 nm thickness with and without 2-nm-thick MgO cap-layers are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The influences of MgO cap-layer on the structure and the magnetic properties are investigated. Fe50PtxPd50−x films epitaxially grow on the substrates at 200 °C. The Fe50Pd50 and the Fe50Pt12.5Pd37.5 films are respectively composed of (001) single-crystals with disordered fcc-based (A1) and bcc-based (A2) structures. The films with x > 25 consist of mixtures of A1 and A2 crystals. The volume ratio of A2 to A1 crystal decreases with increasing the x value from 25 to 50. The in-plane and out-of-plane lattices are respectively expanded and shrunk due to accommodation of lattice mismatch between film and substrate. When the films are annealed at 600 °C, phase transformation to L10 ordered phase takes place. L10 phase transformation of Fe50PtxPd50−x film is promoted for a sample with MgO cap-layer and the order degree is higher than that without cap-layer. Furthermore, L10 ordering with the c-axis perpendicular to the substrate surface is enhanced for the film with cap-layer. The cap-layer is considered to be giving a tension stress to the magnetic film in lateral direction which promotes L10 ordering with the c-axis perpendicular to the substrate. Deposition of cap-layer is shown effective in achieving higher order degree and in enhancing perpendicular magnetic anisotropy with Fe(Pt,Pd) films.

Magnetic force microscope (MFM) tips are prepared by coating silicon tips of 4 nm radius with 20-nm-thick metallic magnetic films with and without 2-nm-thick oxidation protection layers. Iron (Fe) is used as the magnetic material, whereas carbon (C), silicon nitride (Si-N), or silicon carbide (Si-C) is employed as the protection layer. The MFM tips are exposed in an environment of high temperature of 70 °C and high relative humidity of nearly 100%. The effect of protection layer on the spatial resolution is investigated as a function of period of exposure to the environment. The resolution of MFM tip without protection layer deteriorates from 7.2 to 21.2 nm in 10 days. The deterioration is attributed to an increase in the tip radius and a loss of the detection sensitivity caused by oxidation of coated Fe material. In contrast, the resolutions of tips with C, Si-N, and Si-C layers are kept almost constant at 12.1 ± 0.5, 12.1 ± 0.5, and 14.8 ± 2.1 nm for a time span of 10 days, respectively. The coating of a very thin protection layer has been shown effective in keeping the MFM tip performance for a long period of time by preventing the oxidation of coated metallic magnetic material.

Fe50(Pt1–xPdx)50 (at. %, x = 0, 0.25, 0.5, 0.75, 1) alloy thin films are prepared on MgO(001) substrates by using two methods, high-temperature deposition at 600 °C (one-step method) and low-temperature deposition at 200 °C followed by annealing at 600 °C (two-step method). The influence of formation method on the film structure is investigated. L10 crystals epitaxially grow on the substrates when films are deposited at 600 °C. Disordered crystals transform into L10 structure when films are annealed at 600 °C. The films with x > 0.5 consist of L10(001) crystals with the c-axis normal to the substrate surface, whereas the films with x < 0.25 involve small volumes of L10(100) crystals with the c-axis lying in the film plane. Similar final crystallographic orientation is realized for the Fe (Pt,Pd) films prepared by employing the two different methods. The films prepared by one-step method possess island-like surfaces involving side facets, while those prepared by two-step method have very flat surfaces with the arithmetical mean roughness lower than 0.2 nm. The two-step method is effective for preparation of Fe (Pt,Pd) films with flat surfaces.

L1 0 films formed on (001)-oriented underlayers or substrates may involve (100) crystal with the c-axis lying in the film plane in addition to (001) crystal with the c-axis normal to the film surface. In this paper, FePt, CoPt, and FePd alloy films with L1 0 structure are prepared on MgO(001) single-crystal substrates. The c-axis orientation is accurately controlled to be perpendicular by introducing a thin MgO cap layer on magnetic films with disordered structure prepared by low-temperature deposition at 200 °C and by annealing the bilayer films at 600 °C. The phase transformation preferentially occurs along the perpendicular direction in the MgO/(FePt, CoPt, FePd)/MgO sandwich structures. Furthermore, the cap layer promotes L1 0 ordering. The order degrees of FePt, CoPt, and FePd films with and without cap layers, (S w/ , S w/o ), are (0.82, 0.58), (0.36, 0.30), and (0.72, 0.62), respectively. The FePt film with cap layer shows a strong perpendicular magnetic anisotropy and a very low in-plane coercivity because of which the film does not include L1 0 (100) crystal and possesses a high-order degree.

Co x Pt 100-x (at. %) alloy epitaxial films with the close-packed plane parallel to the substrate surface are prepared on MgO(111) substrates heated at 300 °C by varying the Co content of x from 0 to 100. The stacking sequence of close-packed plane (the volume ratios of fcc and hcp crystals, V fcc and V hcp ) and the order degree are quantitatively determined. The films with Pt-rich and nearly equiatomic compositions primarily consist of fcc crystals (V fcc >0.9). With increasing the x value beyond 56, the V hcp value drastically increases. The films with Co-rich compositions consist of mixtures of hcp (V hcp ≈0.8) and fcc (V fcc ≈ 0.2) crystals. The films with 31 ≤x≤ 86 involve metastable ordered phases. The order degree of S L11 ,Bh is kept constant around 0.25 in a compositional range of 31 × 75. From the viewpoints of volume ratios of fcc and hcp crystals and order degree, the crystal structure is determined to vary A1 A1 + SFs (SFs: stacking faults) L1 1 + SFs ⇒L1 1 + Bh (+D0 19 ) ⇒A3 + SFs with increasing the x value. The films including ordered phases show strong perpendicular magnetic anisotropies. It is shown that the uniaxial magnetocrystalline anisotropy energy of Co x Pt 100-x film can be kept >10 7 erg/cm 3 while controlling the saturation magnetization from 600 to 1150 emu/cm 3 .

Nanocomposite magnets consisting of exchange-coupled hard and soft magnetic phases have potentials to achieve high.

FePt and CoPt alloy thin films with L1 0 structure have been investigated for recording media, MRAM devices, etc.

Fe100–xAlx (x = 0, 4, 10, 20, 30 at. %) alloy films of 40 nm thickness are prepared on MgO(001) single-crystal substrates by varying substrate temperature from room temperature to 600 °C. Single-crystal films of (001) orientation with bcc-based disordered A2 structure are obtained for the Al content range of x = 0 - 20 at. %. An ordered phase of DO3 structure is observed in Fe70Al30 films prepared at temperatures higher than 200 °C, whereas (001) oriented single-crystal films of A2 structure are obtained when prepared at room temperature. The film surface profile does not depend much on the film composition, while the surface roughness increases with increasing substrate temperature. Island-like crystals are observed for films prepared at 600°C for all compositions. Difference in lattice spacing measured parallel and perpendicular to the substrate is noted for the single-crystal thin films and it increases with increasing Al content. The lattice strain in single-crystal film is caused possibly to accommodate the lattice mismatch with the MgO substrate. The (001)-oriented single-crystal films with A2 structure show four-fold symmetries in in-plane magnetic anisotropy with the easy magnetization axis A2[100] and the hard magnetization axis A2[110], whereas the films with DO3 ordered structure show almost isotropic magnetic properties.

We investigated the dependence of magnetic properties for Co/Pt100–xPdx multilayer thin films on the concentration in the Pt-Pd alloy layers. Perpendicular magneto anisotropy constant Kp increases with increasing Pt concentration in the Pt-Pd layer, since the interface anisotropy between the Co and the Pt-Pd layers is enhanced by the increase of the Pt concentration. The Curie temperature and the temperature dependence of Kp for the specimens increase with increasing the amount of Pt in the Pt-Pd layer. These results may indicate that the lattice distortion of the Co layer caused by the interface from the Pt-Pd layer becomes larger and the increase of the distortion enhances the interface anisotropy, since the lattice misfit between the Pt-Pd and the Co increases with increasing the Pt concentration. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

FePd alloy films of 1 to 500 nm thicknesses are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The influences of film thickness on the crystallographic orientation, the degree of L 10 ordering, the magnetic property, and the surface roughness are systematically investigated. FePd(001) single-crystal films with disordered structure grow epitaxially on the substrates at 200 °C. The in-plane lattice is expanded to accommodate the lattice misfit between the film and the substrate (−9%). The distortion is decreased with increasing the thickness. When the films are annealed at 600 °C, transformation to L 10 phase occurs. The films thinner than 40 nm consist of L 10(001) variant with the c-axis normal to the substrate surface, where the transformation along the perpendicular direction is preferentially taking place. On the contrary, the films thicker than 100 nm involve L 10(100) and L 10(010) variants whose c-axes lie in the film plane and are rotated around the film normal by 90° of each other. The volume ratio of L 10(001) variant decreases to 0.22, as the thickness increases up to 500 nm. The order degrees of films thinner than 40 nm are 0.6–0.7. With further increasing the thickness, the order degree decreases. The lattice deformation in the disordered FePd film before annealing is effective in enhancing L 10 ordering and aligning the c-axis perpendicular to the substrate surface. The easy magnetization direction varies from perpendicular to in-plane, as the thickness increases from 100 to 500 nm. The magnetic anisotropy is affected by the crystal orientation and the order degree. The films thinner than 2 nm have island-like surfaces, where condensation of deposited atoms on substrate is taking place during the annealing process. When the thickness is increased beyond 10 nm, a flat surface is kept before and after annealing.

Thermally assisted or hybrid magnetic recording system is expected to be a data storage device with high areal density beyond 1 Tb/in2. Several features of the hybrid recording are treated, such as high resolution recording capability by sharp thermal gradient, and pico-second order high-speed magnetization reversal. Since the hybrid recording solves the head field limit problem, the high magnetic anisotropy (Ku) materials with order of 107 erg/cm3 are used for the hybrid recording media. We discuss the candidates of the high Ku materials, FePt and CoPt L10 ordered alloy, Tb-Fe-Co amorphous, and Co/Pd multilayer thin films.

Magnetic force microscope (MFM) tips are prepared by coating Fe(10 nm)/Co50Pt50(x nm)/Ru(5 nm) (at. %) films at 300 °C on Si-base tips of 4 nm radius. The thickness of CoPt layer, x, is varied in a range of 10 – 200 nm. The effects of coating thickness on spatial resolution and switching field of MFM tip are investigated. With increasing the thickness, the resolution deteriorates from 9.4 to 12.1 nm. The switching field increases from 0.675 to 2.025 kOe with increasing the coating thickness from 10 to 200 nm. A tip prepared by coating 100 nm thick Co50Pt50 film which has high resolution and high switching field property is successfully applied to the observation of magnetization structure of high-K u magnetic thin film with L10-ordered structure.

FePt alloy thin films with cap-layers of MgO or C are prepared on MgO(001) single-crystal substrates by using a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The FePt film thickness is fixed at 10 nm, whereas the cap-layer thickness is varied from 1 to 10 nm. The influences of cap-layer material and cap-layer thickness on the variant structure and the L10 ordering are investigated. Single-crystal FePt(001) films with disordered fcc structure (A1) grow epitaxially on the substrates at 200 °C. Single-crystal MgO(001) cap-layers grow epitaxially on the FePt films, whereas the structure of C cap-layers is amorphous. The phase transformation from A1 to L10 occurs when the films are annealed at 600 °C. The FePt films with MgO cap-layers thicker than 2 nm consist of L10(001) variant with the c-axis perpendicular to the substrate surface, whereas those with C cap-layers involve small volumes of L10(100) and (010) variants with the c-axis lying in the film plane. The in-plane and the out-of-plane lattices are respectively more expanded and contracted in the continuous-lattice MgO/FePt/MgO structure due to accommodations of misfits of FePt film with respect to not only the MgO substrate but also the MgO cap-layer. The lattice deformation promotes phase transformation along the perpendicular direction and L10 ordering. The FePt films consisting of only L10(001) variant show strong perpendicular magnetic anisotropies and low in-plane coercivities. The present study shows that an introduction of epitaxial cap-layer is effective in controlling the c-axis perpendicular to the substrate surface.

Co thin films are prepared on GaAs(111) substrates at temperatures ranging from room temperature to 600 ºC by radio-frequency magnetron sputtering. The growth behavior and the detailed resulting film structure are investigated by in-situ reflection high-energy electron diffraction and X-ray diffraction. In early stages of film growth at temperatures lower than 200 ºC, Co crystals with metastable A2 (bcc) structure are formed, where the crystal structure is stabilized through hetero-epitaxial growth. With increasing the film thickness beyond 2 nm, the metastable structure starts to transform into more stable A1 (fcc) structure through atomic displacements parallel to the A2{110} close-packed planes. The crystallographic orientation relationship between the A2 and the transformed A1 crystals is A1{111} || A2{110}. When the substrate temperature is higher than 400 ºC, Ga atoms of substrate diffuse into the Co films and a Co-Ga alloy with bcc-based ordered structure of B2 is formed.

To investigate the basic magnetic and recording characteristics of Co and Co-based alloy thin films, single crystalline and bicrystalline magnetic thin films are prepared by employing an epitaxial thin film growth technique using MgO(110) and (100) single crystal substrates. Uniaxial magneto-crystalline constants ( K u ) and Gilbert's damping constants ( α ) of Co, CoCrTa, and CoCrPt thin films are determined by Torque and FMR measurements. (1100) oriented single crystalline and (1120) oriented bicrystalline Co-based thin films are prepared. K u values of Co, CoCr 16 Ta 4 , CoCr 15 Pt 12 thin films are determined to be 4.5×10 6 , 1.7×10 6 , 3.3×10 6 erg/cc, respectively. The effect of lattice mismatch between the magnetic layer and the Cr alloy underlayer on K u value of CoCr 15 Pt 12 is systematically investigated. The α value of the Co and the Co alloy thin films are determined to be ranging between 0.01–0.04. Recording resolution and noise characteristics of the bicrystalline CoCr 15 Pt 20 disk medium are also examined as a function of angle from the effective easy axis of the disk medium.

Gilbert's damping constants, alpha, of Ni-Fe and Ni-Co thin films are determined by Q-band ferromagnetic resonance (FMR) analysis. alpha is calculated from the resonance width of the FMR spectrum. alpha of Ni85 Fe15 film is found to be 0.0034, which is one-fourth of those of Ni film (alpha=0.013) and Co (alpha=0.013). alpha of the Ni100-x Cox specimens increases with decreasing the Co concentration from 100 to 68 at%, and the alpha value of Ni32 Co68 film has the maximum value of 0.0021. The alpha values of the Ni-Co specimens are nearly the same as those of the Co-Cr-Ta and the Co-Cr-Pt

Magnetic force microscope tips are prepared by coating Si tips of 4 nm radius with magnetic bi-layer film consisting of soft magnetic material of Fe(x nm) and hard magnetic material Co-Pt alloy (20–x nm), 0 ≤ x ≤ 20. The effects of layer thickness ratio and stacking sequence on the spatial resolution and the switching field are investigated. Higher resolutions are observed for tips prepared by coating Co-Pt alloy followed by Fe film deposition compared with those prepared by employing the opposite deposition sequence. The resolution improves from 11.0 to 8.2 nm whereas the switching field decreases from 1525 to 475 Oe with increasing the x value from 0 to 20 nm. The present study has shown a possibility of tuning MFM tip performance by employing a soft/hard dual layer structure.

Exchange stiffness constants ( A ) are determined for a CoCr(Ta, Pt)-alloy system by measuring the temperature variations of saturation magnetization of single-crystal specimens. The A value decreases with increasing Cr concentration. Co–Cr–Pt alloy has a higher A value than that of Co–Cr–Ta alloy with similar Cr concentration.

Magnetic properties are investigated for Co-Cr-Pt thin films deposited on nonmagnetic h.c.p.-Co(Cr,Ru) underlayers with different h.c.p. lattice constants. Higher coercivity, higher coercive squareness, and lower fluctuation field are observed when the h.c.p. lattice constant is close to that of the Co-Cr-Pt recording layer. Temperature dependence of magnetic properties indicates that employment of nonmagnetic Co-Cr-Ru layer is effective to increase the coercivity and to enhance the thermal stability of recording layer.

This study investigates damping constant (alpha) values of soft magnetic materials employing Q-band ferromagnetic resonance (FMR) analyses. The FMR spectra for Ni alloy specimens in addition of Co elements are discussed in detail.

Net assimilation ratio, nitrogen contents and photosynthetic ability of rice plants were measured, using variety Norin No. 37 grown at various planting densities and dosages of fertilizer. Dry matter production in 2 weeks was compared between the community condition and isolated condition in which mutual shading was removed by cutting leaves of the adjacent hills. The results obtained were as follows : 1) The amount of produced dry matter of rice plants under the isolated condition was larger than that under the community condition during the period from 4 to 12 weeks after transplanting. It would be ascribed to that the rice plant under the community could not get sufficient light during the period. 2) Leaf area per hill had an unfavourable effect on assimilation efficiency (ΔW/ΔWAP0), as shown in figure 7, when the light intensity in the community decreased due to the increase of leaf area index. When the value of leaf area index was too high, the reduction of leaf area per hill or dense spacing of planting was considered to be beneficial for assimilation efficiency of the community. 3) Photosynthetic ability of the rice plant had an intimate correlation with the N content in leaf blades. Also the number of glumes per plant had a high correlation with the N content in the plant as well as that in the leaf blade. Accordingly, the number of glumes might indicate the photosynthetic ability of the rice plants at heading time in most cases (Fig. 9)