The tetragonal crystalline structure and magnetic properties of MgO/Rh/(Fe1−xCox)0.9V0.1 and MgO/Rh/(Fe1−xCox)0.9V0.05C0.05 films (0.4 ≦ x ≦ 0.7, thickness t = 2-50 nm) were studied. For both the ...systems, the films with t = 5 nm showed a tetragonal distortion (c/a) of ~1.15 at x = 0.6. Furthermore, in the case of (Fe1−xCox)0.9V0.05C0.05, the films showed a c/a value of ~1.06 even at t = 50 nm. The magnetic anisotropy induced by the tetragonal distortion of films became 1.4 × 107 erg cm−3 for (Fe1−xCox)0.9V0.1 (t = 5 nm) and (Fe1−xCox)0.9V0.05C0.05 (t = 5 nm) films. We also investigated the tetragonal distortion stability of the films using their enthalpy of formation (ΔH) values obtained from density functional theory calculations.
ABSTRACT In the late stages of nuclear burning for massive stars (M > 8 M ), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As ...the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. We find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinos from a star with a mass of 25 M at a distance less than 690 pc with 3 significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.
Near field magnetic force microscopy (NF-MFM) has been demonstrated to locally observe the magnetic fine structures in nanosized recording bits at an operating distance of 1 nm. The nanoscale ...magnetic domains, the polarity of surface magnetic charges, as well as the 3D magnetic fields leaking from the bits are investigated via NF-MFM with a soft NiFe tip. A Fourier analysis of the images suggests that the magnetic moment can be determined locally in a volume as small as 5 nanometers. The NF-MFM is crucial to the analysis of surface magnetic features and allows a wide range of future applications, for example, in data storage and biomedicine.
The uniaxial magnetic anisotropy of tetragonally distorted Fe100−xCox epitaxial films prepared using Rh buffer on a MgO substrate was investigated. The structural relation of body-centered cubic FeCo ...(002)1 1 0 //Rh(0 0 2)1 0 0 //MgO(0 0 1)1 0 0 was maintained up to 20 nm FeCo thickness. The uniaxial magnetic anisotropy constant (Ku1) of the Fe50Co50 films reached a maximum of 1.6 × 107 erg cm−3 when the c/a ratio was 1.15-1.25. The composition dependence of Ku1 of Fe100−xCox (tFeCo = 1.5 nm) was at a maximum at Fe50Co50. These results agree qualitatively with the theoretical value for FeCo films with a tetragonal distortion (c/a = 1.25) and without B2 chemical ordering. Additional uniaxial magnetic anisotropy observed at c/a 1.1 is attributable to the B2 ordering, in addition to the tetragonal distortion.
As the magnetic storage density increases in commercial products, e.g. the hard disc drives, a full understanding of dynamic magnetism in nanometer resolution underpins the development of ...next-generation products. Magnetic force microscopy (MFM) is well suited to exploring ferromagnetic domain structures. However, atomic resolution cannot be achieved because data acquisition involves the sensing of long-range magnetostatic forces between tip and sample. Moreover, the dynamic magnetism cannot be characterized because MFM is only sensitive to the static magnetic fields. Here, we develop a side-band magnetic force microscopy (MFM) to locally observe the alternating magnetic fields in nanometer length scales at an operating distance of 1 nm. Variations in alternating magnetic fields and their relating time-variable magnetic domain reversals have been demonstrated by the side-band MFM. The magnetic domain wall motions, relating to the periodical rotation of sample magnetization, are quantified via micromagnetics. Based on the side-band MFM, the magnetic moment can be determined locally in a volume as small as 5 nanometers. The present technique can be applied to investigate the microscopic magnetic domain structures in a variety of magnetic materials, and allows a wide range of future applications, for example, in data storage and biomedicine.
The fabrication of FePt nanodots with a high structural quality and the control of their switching fields are key issues in realizing high density bit pattern recording. We have prepared FePt dot ...patterns for dots with 15-300 nm diameters by electron beam lithography and re-annealing, and studied the relation between magnetization reversal process and structure of FePt nanodots. The switching field (H sub(sw)) of dot patterns re-annealed at 710 C for 240 min showed a bimodal distribution, where a higher peak was found at 5-6 T, and a lower peak was found at ~2 T. It was revealed by cross-sectional TEM analysis that the structure of dots in the pattern can be classified into two groups. One group has a high degree of order with well-defined 001 crystalline growth, and the other group includes structurally-disturbed dots like 111 growth and twin crystals. This structural inhomogeneity causes the magnetic switching field distribution observed.
The magnetization reversal properties of a single 60 nm diameter Fe nanowire were investigated with an in-field magnetic force microscope (MFM). MFM images were observed in a successively decreasing ...applied field, at various angles between the applied field and the nanowire axis. The results show that the magnetization undergoes a sharp reversal at various angles. When the applied field deviates from the nanowire axis, before complete magnetization reversal, a coherent rotation of magnetic moments inside the nanowire and a stable vortex state at the end of the nanowire are exhibited. The angle dependence of the switching field can be closely described by a curling model, despite the fact the magnetization reversal process is not identical to this model.
Magnetite nanoparticles with controlled size were synthesized by chemical method. Higher deposition temperature and a rapid-raising temperature procedure are favorable to particle size distribution ...and fabrication of monodisperse nanoparticles. The larger nanoparticles can be synthesized by the two-step method. The large nanoparticle (up to 25
nm) without agglomeration was successfully produced. The saturation magnetization of 11
nm magnetite particles was 45
emu/g at room temperature, which is smaller than that of bulk magnetite due to surface effect. Hysteresis of the magnetite nanoparticle was very small, indicating superparamagnetic behavior. The magnetic domains of the 11
nm magnetite nanoparticles were successfully observed by MFM.
► Magnetization reversal of Co–Pt nanodots was studied by magnetic force microscopy. ► The MFM contrast of dots strongly correlates with their switching field (
H
SW). ► Angular dependent
H
SW ...suggests an incoherent rotation rather than a coherent one. ► The incoherent reversal is expected to be due to the damaged shell layer of nanodots. ► LLG micromagnetic simulation confirms the proposal.
The magnetization reversal behavior of a hexagonal close-packed Co–Pt nanodot (50
nm in diameter) array was studied by magnetic force microscopy (MFM). The magnetic switching field (
H
SW) of each dot and the switching field distribution (SFD) for the array were determined by the MFM observation. The results show that the contrast intensity of the dots in the MFM image has a strong correlation with its
H
SW. The angular dependence of the average
H
SW on the direction of the applied field deviates from the coherent rotation model, and appears to reverse by a vortex-like incoherent rotation. It is deduced that the nanodot seems to consist of a hard inner core with high magnetic anisotropy and a soft magnetic shell layer surrounding the core. This core–shell structure results in the magnetic vortex-like incoherent rotation because of an exchange coupling interaction. Shell layers of various thicknesses should result in a broad SFD. This proposal is confirmed by micromagnetic simulation using the exchange coupling model, which is in good agreement with the experimental results.
Ga+ ions at a dose of 0.1at.% (1.5X1014ionscm-2) were irradiated by focused ion beam (FIB) onto L10 FePt films with a 001 crystalline texture normal to the film plane, and two-dimensional patterns ...composed of squares with high-coercivity (L10 structure, 300X300nm2 and 100X100nm2) separated by a soft magnetic region (A1 structure) 100nm wide were fabricated. The magnetic domain structure of patterned film was observed by in-field magnetic force microscopy (MFM). In the remanent state, the domain with magnetization normal to the film surface was observed in the central part of the L10 square, while the narrow domain with reversed magnetization is at the circumference of the square. The magnetization process is discussed based on the MFM observations.
PDF
