Search

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.

Fe thin films are prepared on MgO substrates of (001), (110), and (111) orientations by ultra-high vacuum magnetron sputtering. The magnetostriction behaviors under rotating magnetic fields are observed by using a cantilever method. The relationship between in-plane magnetic anisotropy and magnetostriction behavior is investigated. An Fe(001)bcc single-crystal film is obtained on MgO(001) substrate. A four-fold symmetry in in-plane magnetic anisotropy is observed for the Fe(001)bcc film, where the easy magnetization directions are parallel to bcc[100] and bcc[010]. An Fe(211)bcc bi-crystalline film is formed on MgO(110) substrate and the film also shows an almost four-fold symmetric magnetic anisotropy. The reason is interpreted to be due to an influence of overlap of magnetic anisotropies of two bcc(211) variants with two effective easy magnetization directions which are obtained by projecting bcc[010] and bcc[001] on the bcc(211) plane. An Fe(110)bcc film is epitaxially grown on MgO(111) substrate with two types of variant with the crystallographic orientation relationships similar to Nishiyama-Wasserman and Kurdjumov-Sachs. The Fe(110) film shows an isotropic in-plane magnetic property due to an influence of the variant structure. Usual sinusoidal waveforms of magnetostriction are observed for the Fe(110) film. On the other hand, waveforms measured for the Fe(001) and the Fe(211) films are deformed from sinusoidal shape under low in-plane rotating magnetic fields and the magnetostriction behaviors are similar between the two films. Rectangular waveforms are observed for the bending parallel to easy magnetization directions, whereas triangular waveforms are recognized for the bending parallel to hard directions. The phenomenon is related to the direction difference between applied magnetic field and magnetization in magnetically unsaturated films with in-plane anisotropies. The magnetostriction behavior is influenced by the symmetry of in-plane magnetic anisotropy.

Effects of stress and strain in FePt thin film on $L 1_{0}$ ordering are investigated by employing single-crystal substrate of which lattice mismatch with FePt crystal is varied in a range from −10.3% to +0.8% for 10 nm thick FePt thin film. Thin films are prepared under different conditions; direct deposition at 600 °C, two-step process consisting of 200 °C deposition followed by 600 °C annealing, and the two-step process with MgO cap layer formed on top of the FePt layer at 200 °C. Formation of $L 1_{0}$ -FePt(001) crystal and $L 1_{0}$ ordering is enhanced on a substrate with larger negative lattice mismatch, though the lattice mismatch with substrate is decreased greatly by introduction of misfit dislocation and by lattice bending in FePt material. The lateral in-plane strain in FePt material associated with several factors: substrate material, film morphology, and cap layer has given a strong influence in $L 1_{0}$ -ordered phase formation in FePt thin film.

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.

Atomic-level structures are investigated by high-resolution transmission electron microscopy (TEM) for 10 nm thick $L1_{0}$ -FePt thin films formed on MgO(001) substrate prepared under different conditions. TEM observation has shown that the lattice mismatch with MgO(9%) is decreased greatly by an introduction of misfit dislocation and by lattice bending in FePt material and that such disturbance in FePt crystal lattice is limited within a short distance of less than 2 nm from the MgO interface. Crystal lattice expansion in the lateral direction is recognized in an A1-FePt epitaxial film prepared at 200 °C through the lattice-level analysis of high-resolution TEM image. The lateral in-plane strain in FePt material associated with several factors, substrate, cap layer, and film morphology, is considered to have given a strong influence in promoting the growth of $L1_{0}$ -FePt(001) crystal and enhancing $L1_{0}$ ordering.

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.

Sm17Co83 (at%) films are prepared on bcc-Cr(211), bcc-Fe(211), bcc-Fe65Co35(211), and hcp-Co(1 1 ( _ ) 00) underlayers hetero-epitaxially grown on MgO(110) substrates at 500 °C by using a UHV-MBE system. The growth behavior and the structures are investigated by in-situ reflection high-energy electron diffraction and X-ray diffraction. Sm-Co(1 1 ( _ ) 00) single-crystal films of RT5 ordered structure with the c-axis lying in the film plane grow epitaxially on the underlayers. Small volumes of amorphous phases are interpreted to be involved in the films deposited on these underlayers. The crystal lattice of RT5 magnetic film is slightly deformed from the bulk hexagonal structure, which is caused possibly by the lattice mismatch with the underlayer. The order degree of film deposited on Cr underlayer is higher (S=0.77) than those prepared on Fe, Fe65Co35, and Co underlayers (S: 0.67–0.71). The films show in-plane uniaxial magnetic anisotropies reflecting the magnetocrystalline anisotropy of SmCo5 crystal.

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.

Sm 17 Co 83 /Fe 65 Co 35 (at. %) multilayer films are prepared on MgO(110) substrates at 500 °C by ultra-high vacuum molecular beam epitaxy. The film crystallographic properties during formation are investigated by in-situ reflection high-energy electron diffraction. The 1st Fe–Co layer epitaxially grows on the substrate with two variants whose orientations are rotated around the film normal by 180° each other. The 1st Sm–Co layer formed on the 1st Fe–Co layer involves a small volume of amorphous phase in addition to epitaxial (11¯00)) crystal of RT 5 structure with the c -axis lying in the film plane. The crystallographic quality of 2nd Fe–Co layer is inferior to that of 1st Fe–Co layer. The 2nd Sm–Co layer is composed of polycrystal and amorphous phases. The crystallographic properties of Sm–Co and Fe–Co layers are delicately influenced by those of lower layers. The Sm–Co/Fe–Co multilayer films involving Sm–Co(11¯00) RT 5 epitaxial crystal show in-plane uniaxial magnetic anisotropies reflecting the magnetocrystalline anisotropy of SmCo 5 crystal. The coercivity increases with increasing the volume of Sm–Co(11¯00) RT 5 crystal.

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.

Magnetostrictive behaviors of Fe100− x B x (001), $x=0$ , 5, and 13 at. %, single-crystal films are studied in comparison with those of poly-crystal Fe–B films under rotating magnetic fields. The output waveform of poly-crystal Fe–B film is sinusoidal and the saturation magnetostriction, $\lambda _{s}$ , varies from negative to positive with increasing the B composition, $x$ , from 0 to 13 at. %. On the other hand, the output waveform of single-crystal Fe–B film is bathtub-like when measured along the easy magnetization axis of bcc[100], while it changes to triangular when measured along the hard magnetization axis of bcc[110]. The output waveform is strongly influenced by the magnetocrystalline anisotropy under a magnetic field of 1 kOe which is larger than the anisotropy field of the material. Variations of $\lambda _{{\mathbf {100}}}$ and $\lambda _{{\mathbf {111}}}$ values are estimated as a function of B content. $\lambda _{{\mathbf {100}}}$ of Fe–B film shows a positive value and increases with increasing the B content from 0 to 13 at. %, while the value of $\lambda _{{\mathbf {111}}}$ changes from negative to positive with increasing the B concentration. The B content dependence of $\lambda _{s}$ for poly-crystalline Fe–B samples is explained by considering the B content dependence of $\lambda _{{\mathbf {100}}}$ and $\lambda _{{\mathbf {111}}}$ determined with single-crystal film samples.

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.

Effects of magnetic material, coating thickness, and tip radius on the magnetic force microscope (MFM) spatial resolution and the switching field have been investigated. MFM tips are prepared by coating soft and hard magnetic materials on non-magnetic Si-base tips. MFM spatial resolutions better than 8 nm are obtained by optimizing the coating layer thickness at around 20 nm on the Si tips with top radius of 3 – 5 nm. The switching field can be increased greater than 1 kOe by coating a high-Ku magnetic material and by increasing the coating thickness. The tips are successfully applied to the observations of magnetic thin films which include magnetization structures less than 20 nm in length.

Fe, Co, and Ni thin films are deposited on GaAs(110) substrates at room temperature using a radio frequency magnetron sputtering system. The film thickness is varied in a range between 1 and 40 nm. The growth behavior and the detailed resulting film structure are investigated by reflection high-energy electron diffraction and pole-figure X-ray diffraction. The bcc single-crystals nucleate on the substrates for all the film materials, though the bcc structure is metastable for Co and Ni materials. The metastable structure is stabilized through heteroepitaxial growth. The crystallographic orientation relationship is bcc(110)[001]||GaAs(110)[001]. With increasing the thickness beyond 2 nm, the bcc-Co and bcc-Ni crystals start to transform into fcc structure through atomic displacements parallel to the slide planes of bcc( $10\bar 1$ ), bcc( $01\bar 1$ ), bcc(011), and bcc(101) that are 60° inclined from the surface. The Co and Ni films thicker than 2 nm involve fcc crystals. On the contrary, Fe films possess bcc structure for all the thicknesses.