Using magnetic force microscopy (MFM), we investigated the effect of compositional separation (CS) on the magnetic domain configurations in Co78Cr22 films. Scanning electron microscopy of chemicallyetched microstructures and nuclear magnetic resonance studies showed that a film deposited at room temperature (RT) was compositionally homogeneous, while a film deposited at 200°C was in a compositionally separated state. The MFM image of the RT film showed a typical maze-type domain structure. In contrast, the image of the 200°C film suggested the existence of a finer, discontinuous domain structure. Point magnetic recording, using a Permalloy tip, produced magnetic dots down to between 0.15 and 0.30 μm in diameter in the 200°C film. No such magnetic dots, however, were observable for the RT film. These MFM results are consistent with CS promoting a change from a continuous to a particulate type magnetic microstructure suitable for high density magnetic recording.
To study the magnetic behavior in a perpendicular magnetic film, the magnetic energy density of the film is calculated on the assumption that the film is a three-dimensional array of ferromagnetic blocks. From the energy density, MH loop, the angular dependence of the coercive force He and the anisotropy field HK are calculated for the fanning and parallel rotation mechanisms. It is found that Hkf>Hcp>Hcf>Hkp,where f and p denote the fanning and parallel rotation mechanisms, respectively. These results for the fanning mode agree with many previous experimental results.
An experiment was carried out to investigate the magnetic and physical properties of Sm-Fe-Cu-Nb-N compounds. These compounds were prepared by nitrogenation of an Sm2Fe17 compound with added x wt%Cu and 0.5 wt% Nb powders (about 30%μm) in high-purity nitrogen gas at pressures of 98 kPa and 4.9 MPa, and temperatures of 475-600°C for 1-4 h. The grain size of an ingot of Sm2Fe17 with added Cu and Nb was about 60% of that of an Sm2Fe17 ingot. It was found that the value of the anisotropy field (HA) in these compounds increased with increasing Cu (up to 1 wt%) concentration, while the saturation magnetization (σs) decreased. The values of HA and σs in nitride of Sm2Fe17 with added 1.0 wt%Cu and 0.5 wt%Nb were 10.03 MA/m and 189.8 × 10-6 Wb·m/kg, respectively. The magnetic and physical properties of an anisotropic Sm2Fe17 Cu0.148Nb0.067N2.97 epoxy-bonded magnet were Jr=0.83 T, HcJ=474 kA/m, HcB=351 kA/m, (BH)max= 103 kJ/m3, and D=5.50 Mg/m3. The reversible temperature coefficients (from 25 to 125°C) of the bonded magnet were α(Jr)= -0.058%/°C, and β(HcJ ) = -0.496%/°C.
The crystal structure and thermoelectric properties of Mn1-xCrxTe (0≤x≤0.3) films prepared on glass substrates by vacuum evaporation were investigated. X-ray diffraction measurements showed that the solubility limit of Cr in the NiAs-type MnTe phase for Mn1-xCrxTe films is x=0.06. For films in which 0≤x≤0.06, the Neel temperature TNopt, which was determined from the deflection point in the temperature dependence curve of the optical band gap, shifts strongly toward higher temperatures from TNopt,=327 K (x=0) to TNopt,=460 K (x=0.06) with an increase in x. The Seebeck coefficient S of the films reaches a maximum around TNopt, indicating that the enhancement of S can be attributed to the magnon-drag effect. On the other hand, for x >0.06, the temperature at which S reaches a maximum does not change with x, and S decreases markedly owing to the presence of a metallic Cr2Te3 phase.
Giant magnetoresistance (GMR)in Co/Cu metallic multilayers was measured with a current perpendicular to the plane (CPP) at room temperature. Micro-pillar structures with a height of 1.0μm and widths ranging from 15 to 25 μm, fabricated by using optical lithography and Ar ion etching techniques, were used for the measurement. The CPP MR in Co (3 nm)/Cu (2 nm) multilayers was found to be 2.5 times larger than the MR with a current in the film plane (CIP).
Scanning tunneling microscopy (STM) studies were carried out to clarify the initial growth mechanisms of ultrathin Fe films on GaAs(001) substrates. Observation revealed that Fe atoms initially form many small clusters on the flat terraces of the c(4 × 4) reconstructed GaAs(001) surface at room temperature. The typical size of the Fe clusters is about 1.5 nrn, which is nearly equal to the size of the basis structure of the c(4 × 4) reconstruction. It is also shown that the formation of the Fe clusters depends on the reconstruction of the GaAs(001) surface and the temperature of thermal treatment.
To determine the possibility of discriminating multisources in the brain by using a 3-D magnetoencephalogram (MEG), measurements were made of magnetic fields produced by two and three current dipoles implanted in a spherical head model and a human cranium model. The 3-D MEG measurement was made by using a 3-D second-order gradiometer connected to three rf-SQUIDs, which can detect magnetic field components perpendicular to and tangential to the scalp. The MEG distribution perpendicular to the scalp was not helpful for estimating the location and number of sources, owing to the lack of a dipole pattern. By referring to the MEG distribution tangential to the scalp, however, two and three current sources could be clearly discriminated in both a spherical head model and a cranium model. It was found that this MEG measurement tangential to the scalp could provide information on new constrained conditions for calculation of the inverse problems with multi-sources.
The magnetic orientations of human red blood cells (RBCs) were investigated under strong magnetic fields up to 8 T by measuring the electrical resistivity of suspensions containing RBCs. The electrical resistivities of the suspensions were decreased by applying magnetic fields parallel to the electric field. This phenomenon indicates that RBCs are redirected by a magnetic field. It was observed that the degrees of magnetic orientation of RBCs vary according to the surrounding medium, such as plasma, serum, or phosphate buffer solution. The changes in the electrical resistivity of samples of 40% RBCs suspended in phosphate buffer solution, serum, and plasma were 15%, 8%, and less than 4%, respectively. The electrical resistivity of anticoagulated whole blood was not changed by the application of magnetic fields up to 8 T. These results show that albumin, globulin, fibrinogen, and leukocyte prevent the magnetic orientation of RBCs in blood.
Oxide-superconductor bulk materials that can act as magnets after field cooling were made by a modified quench-and-melt-growth (QMG) process. To enlarge QMG crystals having a fine 211 phase in the matrix of a crystalline 123 phase, a modi tied QMG process was developed by adding a seeding technique and a Pt addition technique to the original QMG process. Enlarged QMG bulk superconductors were operated as high-field permanent magnets. A bulk magnet 70 mm in diameter and 35 mm in thickness had trapped maximum values of 4.5 T, 2.5 T, and 0.99 T at 40 K, 63 K, and 77 K, respectively. Thermornagnetomechanical instability leading to quenching phenomena was not observed above 40 K.