Bit patterned media is a possible candidate for developing next-generation ultra-high-density data storage, therefore, the importance of shape, of techniques for fabricating magnetically monodisperse dots, and of research on materials that have high uniaxial magnetocrystalline anisotropy energy such as L10-FePt is increasing. Furthermore, although the magnetic characterization of each isolated patterned dot is a crucial matter, there is a fundamental difficulty in measuring infinitesimal magnetic moments. On the basis of the idea of estimating the magnetic properties of a single dot by measuring several hundred million monodisperse dots, we investigated a process for fabricating monodisperse FePt dots and a magnetization process. In this report, we propose a novel fabrication procedure that consists of a combination of pre-patterning Pt/Fe film and post-annealing with rapid thermal annealing. Pt/Fe dots with a pitch of 100 nm and thickness of 3.75 nm were pre-patterned by using an electron beam lithography technique and rapidly heated up to 800℃, which lead to a lower dispersal of dots that was promoted by a hard-magnetic property. Under a Fe-rich composition condition for Fe60Pt40, 90% of the FePt dots showed a coercive force of over 15 kOe.
In this study, we analyzed the surface morphology for the samples with thermal insulation layer (fcc(002)-MgO) / orientation control layer (bcc(002)-CrMn) / orientation inducing layer (amorphous CoW, NiTa, CrTi), especially focusing on atomic diffusion during the high-temperature process used to create the samples. Furthermore, we proposed a new design to realize a granular medium with the columnar nanostructure. Observation of the surface morphology of the MgO layer revealed that only when CrMn was used, a topological surface structure like a network (inverse opal structure) with a period of 10 - 20 nm and a height of about 2 nm was formed. Regarding this structure, 1) a CrMn grain boundary existed below where an upheaval structure was formed on the surface, 2) the elements constituting the amorphous layer exist in the grain boundary of the CrMn layer. These results suggest that the network-shaped upheaval structure on the surface of the MgO layer is brought by boundary diffusion of the elements constituting the amorphous layer from the amorphous layer into grain boundaries of the CrMn layer. Based on the above results, we have newly proposed a schematic model of HAMR media. First, to form isolated nuclei, a pure-FePt island-like layer with L10 ordered structure is deposited on the network-shaped upheaval structure of the MgO layer. Next, to realize a columnar nanostructure, a two-phase precipitated FePt-oxide layer is sputtered.
We study the magnetic anisotropy (MA) of magnetoplumbite (M)-type ferrites by calculating the electronic structure of clusters formed with an Fe3+ ion and O2- ions. Spin-orbit interaction (LS coupling) is taken into account. It is shown that the p-d mixing between the Fe and O ions and local lattice distortion are crucial to understand the MA of M-type ferrites. Calculations of MA for M-type ferrites doped with Fe2+ or Co2+ ions demonstrate the importance of local lattice distortion on MA. It is shown that Fe2+ ions doped into 2a-site produce metamagnetic character when a compressive deformation along c-axis is introduced. It is also shown that the Co2+ ions doped onto 4f1 site may enhance the uniaxial MA when a compressive deformation is introduced.
The structural and magnetic properties of (Sm,Y)(Fe,Co)12-xTix (x = 0.5, 0.6) prepared by arc melting and rapid quenching are investigated. The formation of the TbCu7-type phase were facilitated with decreasing amount of Ti concentrations, and many amount of TbCu7-type phase was observed for arc melted alloy at low Ti concentrations (x = 0.5). In the contrast, the volume fraction of TbCu7-type phase was reduced remarkably for rapidly quenched alloy. This shows that the formation of the ThMn12 structure was facilitated by rapid quenching at low Ti concentrations. When compared with the same amount of Ti concentrations (x = 0.5), the value of saturation magnetization of rapidly quenched alloy which was 1.55 T was higher than that of arc melted alloy.
Ring samples are often used for measuring the DC magnetic characteristics of magnetic material. In this measuring method, stress and strain are induced into a specimen by winding coils on the ring samples. The magnetic characteristics of the samples might be affected by the inverse-magnetostriction phenomenon, which is caused by compressive stress on the ring samples. Hence, by using ring sample of a material with a positive magnetostriction constant, DC magnetic characteristics were measured both with and without the polymer case in order to prevent winding stress. As a result, it was confirmed that the magnetic characteristics of the ring samples were changed by the inverse-magnetostrictive effect induced by compressive stress.
An electronic and magnetic phase diagram of a mixed anion layered compound, Sr2CrFeAsO3−δ, is demonstrated. Sr2CrFeAsO3−δ is composed by a carrier conducting FeAs layer and carrier blocking Sr2CrO3−δ layer. Polycrystalline Sr2CrFeAsO3−δ samples were prepared by solid-state reaction. The oxygen deficiency (δ) of the samples was determined using an assumption of a linear relation between δ and lattice volume (V). The δ-V relation was based on the V of several nominal compositions of polycrystalline samples with a smaller second phase. An electronic and magnetic phase diagram of Sr2CrFeAsO3−δ that considers δ and temperature (T) was created on the basis of electrical resistivity measurements and 57Fe Mössbauer spectroscopy measurements. A magnetic Fe sublattice of Sr2CrFeAsO3−δ exhibited a stripe-type antiferromagnetic (AFM-s) phase for 0.124 ≤ δ ≤ 0.210 at T < 60 K and an internal magnetic field (Hint) distributed antiferromagnetic (AFM-DH) phase for 0.247 ≤ δ ≤ 0.256 at T < 53 K.
This paper reports the effect of Ga composition on the static and dynamic magnetic properties of 10-nm-thick Fe-Ga polycrystalline films. As for the static magnetic properties of these films, the saturation magnetization (4πMs) decreased as the Ga composition increased. This feature is similar to that of Fe-Ga bulk alloy. The saturation magnetostriction (λs) also increased as the Ga composition increased, but these values were lower than those of Fe-Ga bulk alloy. As for their dynamic magnetic properties, the damping constant (α) decreased from 0.034 to 0.012 as the Ga composition increased, suggesting that the magnetization of Fe-Ga films with Ga compositions below 25 at.% switched slowly in the high frequency range. Therefore, the effect of Ga composition on α and λs is opposite between the two, indicating that this feature differs from those in Ni-Fe and Fe-Si binary alloy films.
We developed a sensitive magnetostriction measurement system of magnetic thin film specimens using a Michelson interference. When magnetic field is applied parallel to the film plane of the cantilevered specimen, the magnetostriction of the film makes the specimen slightly bend, and the movement of the interference patterns is observed depending on the deflection d of the specimen. Variation of d can be detected with the precision of about one hundredth of wavelength of laser beam. The magnetostriction constant λ110 of Fe(001) single crystal thin film deposited on MgO(001) single crystal substrate with film thickness of 61 nm was estimated to be (1. 4±0.27)×10-5 from the deflection of 2.6±0.5 nm.
The effects of magnet size, separation, and rotation pattern on the strength and uniformity of a magnetic field and the torque acting on magnets are discussed regarding the design of a mangle-type magnetic field source. A finite-element simulation revealed that the maximum magnetic field increased as the diameter of the magnets increased or magnet separation decreased. A uniform magnetic field is possible when the rotation pattern of the magnets adopts a circular arrangement of magnetization for zero-field while a high torque acts on the magnets. The simulation results were verified with a prototype, although the maximum field was smaller than the simulation.
A novel built-in CPU liquid cooling system that dispenses with a cooling fan is proposed for a high-end laptop PCs. This system consists of a liquid cooling jacket adhered to a CPU, a heat radiation flat plate on the back cover of a monitor, and magnetically driven micro-pumps. First, the size of the plate and the flow rate of coolant were determined on the basis of a thermal resistance method. Next, a micro-pump that uses a flapping elastic plate was designed and fabricated to be less than 8 mm in height, which included a drive coil. Last, to increase the load flow rate to the target value, multiple pumps were serially connected. As a result of a heating test, the liquid cooling system equipped with the two micro-pumps in series, successfully dissipated heat up to 50 W.
Miniaturization and high efficiency of electronic device is required. The elements such as inductors and capacitors used in electronic equipment, are working to miniaturization and high efficiency by higher frequency. Along with the higher frequency of the driving frequency, AC resistance increases due to iron loss and copper loss. So, the authors have developed Magnetocoated wire (MCW) that has a magnetic layer around the copper wire to reduce the AC resistance. MCW reduces AC resistance because a magnetic layer leads a magnetic flux. As a result AC resistance in coil using MCW was reduced 32.1% in 1 MHz, 24.7% in 100 kHz, 20 % in 10 kHz.
Switched reluctance (SR) motors have a simple and robust structure, and low cost. However, torque and efficiency of conventional SR motors are lower than those of rare-earth permanent magnet motors. To improve the disadvantages, several kinds of special-structured SR motors, including axial-gap-type and permanent-magnet-assisted-type, have been proposed. This paper investigates a transverse-flux-type SR motor (TFSRM). The TFSRM is designed by using a finite element method (FEM), and the prototype tests are carried out. In addition, further improvement of the performance of TFSRM is discussed based on the prototype tests results.
A field-winding type claw-pole motor has a three-dimensional complicated structure. In addition, its characteristics depend on not only an armature current but also a field-current. Therefore, to estimate the characteristics of the field-winding type claw-pole motor, three-dimensional electromagnetic field analysis combined with its drive circuit is required. In a previous paper, three-dimensional relcutance network anaysis (RNA) model of the claw-pole motor was proposed and the validity of the proposed model is proved by comparing with the results of torque characteristics obtained from finite element method (FEM). This paper presents a method for calculating eddy current loss on the rotor surface of the claw-pole motor based on RNA.
A magnetic-geared motor that an electric motor and a magnetic gear are magnetically combined has come to attract attention recently. In previous papers, several magnetic-geared motors were presented, and the feasibility and usefulness were demonstrated. However, the efficiencies of those prototype motors are not enough high. In this paper, efficiency improvement of a magnetic-geared motor is investigated from the view point of increasing torque and reducing losses. A prototype motor is designed by using three-dimensional finite element method (3D-FEM). The test results indicate that the efficiency is improved and that the prototype motor can be applied to walking support machines.
Magnetic gears can change the speed and torque without any mechanical contacts. Therefore, it has a low vibration and acoustic noise, and maintenance-free operation. Several kinds of magnetic gears were proposed. Among them, a flux-modulated type magnetic gear has higher torque density than other kinds of magnetic gears. In a previous paper, an interior permanent magnet (IPM) structure was presented. It was demonstrated by finite element analysis (FEM) that eddy current loss in the magnets can be reduced remarkably. This paper describes the comparison of the IPM structure with surface permanent magnet (SPM) structure in experiment and discusses a performance improvement of the IPM gear from the view point of the rotor structure.
Acupuncture and moxibustion are forms of oriental medicine that are used in medical treatment to stimulate the nerves of the body. In moxibustion treatment, thermal stimulation is applied through heat conduction from the outside of the skin by burning moxa near the skin, so there is an inevitable disadvantage of burning the skin. In this paper, we propose a novel applicator system of non-contact induction heating for avoiding this disadvantage. The acupuncture inserted in the skin is heated by electromagnetic induction heating and heat stimulation is applied selectively near the target to be stimulated. In addition, the configuration of the exciting coil of the proposed applicator allows the inside of the skin to be heated, so a thermal stimulation is possible near subcutaneous cells. We discussed the magnetic flux density distribution, heat capacity, and rising temperature theoretically and experimentally. We confirmed that the proposed is effective.
This paper presents torque and efficiency improvement of high-speed permanent magnet (PM) motors for cooling-fans from the view point of the rotor structure. The first candidate is surface permanent magnet (SPM) motor, which has bonded Nd-Fe-B polar anisotropic magnets in order to obtain large torque and low iron loss. The second one is interior permanent magnet (IPM) motor, which has a two-layer-type rotor in order to obtain large reluctance torque. The both PM motors are compared in terms of torque and efficiency by using three-dimensional finite element method (3D-FEM). The IPM motor, which demonstrates higher efficiency, is prototyped and demonstrates lager torque and higher efficiency in comparison with a previous cooling-fan motor.
An analytical method taking deterioration of magnetic core due to machining process into consideration and finding the optimum processing method are essential to development of high-efficiency electric machines. In a previous paper, simplified Landau-Lifshitz-Gilbert (LLG) equation, which expresses the behavior of magnetizations inside the magnetic core, was used for calculating magnetic properties of the electromagnetic steel sheet. It was demonstrated that the proposed method can express the dynamic behavior of the magnetic core including manor loops. This paper presents a novel prediction method of magnetic properties in the machined magnetic core by using the simplified LLG equation.
Thin steel plates are widely used in various industrial products, and these products demand plates with a high-quality surface. However, there is a problem in that surface quality and metal plating are degraded during transport. As a solution to this, non-contact transport of steel plates electromagnetic force has been proposed. It was previously confirmed that, by applying a magnetic field in the horizontal direction, the levitation stability of transported thin steel plates improved under different transport conditions. However, the positions at which to install the electromagnets in the horizontal direction has not yet been investigated. Therefore, in this report, we investigated the positions at which a magnetic field should be applied in the horizontal direction and confirmed that the positions are related to improving the levitation stability of steel plates.
In the conveyance systems of production lines for thin steel plates, there is a problem in that the quality of the plate surface deteriorates because the plates are always in contact with rollers. To solve this problem, electromagnetic levitation technologies have been studied. When an ultrathin and flexible steel plate is to be levitated, controlling the levitation becomes difficult because the plate undergoes increased flexure. In this study, we herein propose a method of levitating an ultrathin steel plate that is bent to an extent that does not induce plastic deformation. To investigate the levitation stability of an ultrathin steel plate, we applied disturbance cancellation control in a bending and levitation system. The object of electromagnetic levitation was a rectangular zinc-coated ultrathin steel plate (SS400) with a length of 800 mm, width of 600 mm, and thickness of 0.19 mm. A vibrator was attached below three frames on which an electromagnet unit was installed so that the frames could be vibrated up and down. We conducted experiments on levitation performance when the electromagnet was displaced by frame vibration in the system. The results show that stable levitation can be realized even with an input external disturbance when levitating at the optimum bending angle.
Research was conducted on non-contact transfer technology for applying magnetic levitation technology that uses electromagnets to thin steel plates. We previously succeeded in improving the levitation performance by bending a thin steel plate within a range that did not plastically deform it. In this study, to clarify the vibration mechanism of the steel plate during levitation, we performed a modal analysis, a frequency response analysis on a plate, and a bending and levitation experiment with a type of disturbance that has the most influence on such plates. As a result, it was found that the bending and magnetic levitation is effective for improving the levitation performance because the vibration mode became dominant when bending the thin steel plate and the levitation performance could be maintained even when the disturbance was input.
We investigate the effect of the ionic strength of surrounding NaCl solutions of an iron-oxide chitosan hydrogel (FeOx-CH) on magnetic relaxation of the FeOx NPs. The magnetic relaxation of the FeOx NPs is examined using dynamic magnetic susceptibility measurement. Swelling ratio (SR) is also measured after the FeOx-CH is immersed to various NaCl concentrations. SR of the FeOx-CH decreases as the NaCl concentration increases. This trend is explained by considering the osmotic water flow in the FeOx-CH. The peak in frequency dependence of the imaginary part of the susceptibility (χ ”) is found around 200 Hz. In addition, the position of the χ ” peak frequency shifts to lower frequencies as the NaCl concentration increases. The observed frequency shift is inferred to be due to the suppression of the Brownian relaxation caused by the decrease of SR of the FeOx-CH as the NaCl concentrations increases. An effective viscosity change of 6.8% due to the change in the NaCl concentration is also estimated via analytical calculation.