Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.233-241
Time Resolved Effect of Heat Dispersion on Magnetic Stability in Ferromagnetic Ising Thin-Films, Monte Carlo Simulation
In this work, Monte Carlo simulation was used to investigate the magnetization properties of thin ferromagnetic films under a perturbation from a supplied heat pulse on one surface of the films. The finite difference method was used to extract the local temperature of each layer of the films as a function of time for various heat source power and heating period. Then, with the variation of the films temperature, Metropolis method was used to update the magnetic moment in magnetic grain, under the Ising framework and using the FePt parameters. With the extracted magnetization profiles, the relationship between magnetization relaxation in accordance with relevant heat parameters and films thickness was reported and discussed, with a purpose to form a database for future use.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.242-244
Width-Dependent Transition of Magnetic Domain Configuration in Nanostructured CoFe/Pt Multilayered Nanowires
We report on the basis of experiments that magnetic domain structures exhibit a transition between single and dendrite domains with respect to the width of ferromagnetic nanowires. This transition is directly observed in CoFe/Pt multilayered nanowires having a width in the range of 580 nm to 4.2 μm with a magnetic force microscope. Nanowires wider than 1.5 μm show typical dendrite domain patterns, whereas the nanowires narrower than 690 nm exhibit single domain patterns. The transition occurs gradually between these widths, which are similar to the typical widths of the dendrite domains. Such a transition affects the strength of the domain wall propagation field; this finding was made by using a time-resolved magneto-optical Kerr effect microscope, and shows that the domain wall dynamics also exhibit a transition in accordance with the domain configuration.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.245-250
Ferromagnetic Resonance and X-Ray Reflectivity Studies of Pulsed DC Magnetron Sputtered NiFe/IrMn/CoFe Exchange Bias
Ferromagnetic resonance and X-ray specular reflectivity measurements were performed on Ni81Fe19/Ir20Mn80/Co90Fe10 exchange bias trilayers, which were grown using the pulsed-DC magnetron sputtering technique on Si(100)/SiO2(1000 nm) substrates, to investigate the evolution of the interface roughness and exchange bias and their dependence on the NiFe layer thickness. The interface roughness values of the samples decrease with increasing NiFe thickness. The in-plane ferromagnetic resonance measurements indicate that the exchange bias field and the peak-to-peak line widths of the resonance curves are inversely proportional to the NiFe thickness. Furthermore, both the exchange bias field and the interface roughness show almost the same dependence on the NiFe layer thickness. The out-of plane angular dependent measurements indicate that the exchange bias arises predominantly from a variation of exchange anisotropy due to changes in interfacial structure. The correlation between the exchange bias and the interface roughness is discussed.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.251-254
Electron Magnetic Resonance of Eu2+ in SrCl2:Eu Single Crystal
The electron paramagnetic resonance (EPR) of the Eu2+ ion in SrCl2:Eu single crystal has been investigated using an
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.255-260
Thermal Properties of Mn-doped LiNbO3 Crystals from Magneto-Optical Transitions
In this study, we determine that the electron paramagnetic resonance line-width (EPRLW) is axially symmetric about the c-axis and analyze the spin Hamiltonian with an isotopic g-factor of 1.9920 at a frequency of 9.5 GHz. It should be noted that the electron paramagnetic resonance signals are Lorentzian. Our findings show that the EPRLW decreases exponentially with an increase in the temperature; i.e., its temperature dependence in the range 300-400 K obeys Arrhenius behavior, this kind of temperature dependence indicates an off-center a motional narrowing of the spectrum when Mn2+ impurity ions substitute for Nb5+ ions. The specific heats follow a linear dependence suggesting a simple Debye
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.261-264
Interfacial Properties in Cu-phthalocyanine-based Hybrid Inorganic/Organic Multilayers
Interfacial properties of 5 nm MgO(001)/7 nm Fe(001)/1.8 nm MgO(001)/t nm Cu-phthalocyanine (CuPc) hybrid multilayers with t = 0, 1, 7, and 10 were investigated by using x-ray photoemission spectroscopy (XPS). Rather sharp interfacial properties were observed in the CuPc films grown on an epitaxial MgO/Fe/MgO(001) trilayer than a MgO/Fe(001) bilayer. This work suggests a new way to improve device performance of organic spintronic devices by utilizing an artificially grown MgO(001) thin layer.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.265-270
Enhanced Low-field Magnetoresistance of La0.7Sr0.3Mn1+
We report improved low-field magnetoresistance (LFMR) effects of the La0.7Sr0.3Mn1+
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.271-274
Dosimetry Application of Irradiated D-fructose using the Electron Paramagnetic Resonance
We examine dosimetry application of irradiated D-fructose materials using electron paramagnetic resonance (EPR). Consequently, we consider that fructose is one of best dosimetry materials. We found that fructose is one of best candidates for dosimetry due to high linearity tilt of EPR signal intensity as a function of dose, irrelevant to photon energy, constant fading value. Also, our results show that fructose materials can be applied as a radiation detector to very weak radiation doses of 0.001 Gray by using EPR at a low temperature (T = 220 K).
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.275-279
Robust Design of Air Compressor-Driving Quadratic Linear Actuator in Fuel Cell BOP System using Taguchi Method
The linear actuator has the inherent drawback of air gap variation because its linear motion is usually guided by the springs, which destabilizes the dynamic performance. In order to design the linear actuator to be insensitive to air gap, this paper describes the robust design of the air compressor driving linear actuator using Taguchi method. The orthogonal arrays are constructed with selected control factors and noise factor for minimum experiment. The control factors are thickness of inner magnet, height of upper yoke, thickness of outer magnet and thickness of lower yoke while noise factor is airgap. The finite element analysis using commercial electromagnetic analysis program “MAXWELL” are performed instead of experiment. ANOVA are performed to investigate the effects of design factors. In result, the optimal robust linear actuator which is insensitive to air gap variation is designed.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.280-284
Analytical Study Considering Both Core Loss Resistance and Magnetic Cross Saturation of Interior Permanent Magnet Synchronous Motors
This paper presents a method for evaluating interior permanent magnet synchronous motor (IPMSM) performance over the entire operation region. Using a d-q axis equivalent circuit model consisting of motor parameters such as the permanent magnetic flux, copper resistance, core loss resistance, and d-q axis inductance, a conventional mathematical model of an IPMSM has been developed. It is well understood that in IPMSMs, magnetic operating conditions cause cross saturation and that the iron loss resistance − upon which core losses depend − changes according to the motor speed; for the sake of convenience, however, d-q axis machine models usually neglect the influence of magnetic cross saturation and assume that the iron loss resistance is constant. This paper proposes an analysis method based on considering a magnetic cross saturation and estimating a core loss resistance that changes with the operating conditions and speed. The proposed method is then verified by means of a comparison between the computed and the experimental results.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.285-290
Comparisons of Linear Characteristic for Shape of Stator Teeth of Hall Effect Torque Sensor
Electric Power Steering (EPS) system is superior to conventional Hydraulic Power Steering (HPS) system in aspect of fuel economy and environmental concerns. The EPS system consists of torque sensor, electric motor, ECU (Electric Control Unit), gears and etc. Among the elements, the torque sensor is one of the core technologies of which output signal is used for main input of EPS controller. Usually, the torque sensor has used torsion bar to transform torsion angle into torque and needs linear characteristic in terms of flux variation with respect to rotation angle of permanent magnet. The torsion angle of both ends of a torsion bar is measured by a contact variable resistor. In this paper, the sensor is accurately analyzed using 3D finite element method and its characteristics with respect to four different shapes of the stator teeth are compared. The four shapes are rectangular, triangular, trapezoidal and circular type.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.291-297
Efficient Methodology for Reliability Assessment of Electromagnetic Devices Utilizing Accurate Surrogate Models Based on Dynamic Kriging Method
This paper presents an efficient methodology for accurate reliability assessment of electromagnetic devices. To achieve the goal, elaborate surrogated models to approximate constraint functions of interest are generated based on the dynamic Kriging method and a hypercube local window. Then, the Monte Carlo simulation scheme is applied to the surrogate models. This leads to reducing computational cost dramatically without degrading accuracy of the reliability analysis. The validity of the proposed method is tested and examined with a mathematical example and a loudspeaker design.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.298-301
The Effects of Lift-Off from Wall Thinning Signal in Pulsed Eddy Current Testing
In order to know the effect of surface irregularity in the detection of local wall thinning of pipeline using pulsed eddy current (PEC), the lift-off effects on PEC signal have been investigated. Three kinds of parameters in the PEC signal, which is “peak amplitude”, “time to peak amplitude” and “time to zero crossing” are analyzed to separate the lift-off effects in the PEC signal. The distance from sensor to the bottom of sample which is the total thickness of combined insulator and sample is kept constant. The magnitude of the differential peak amplitude is increased with increasing sample thickness, the time to peak amplitude is increased with increasing the sample thickness. To determine the effect of lift-off, a number of balanced transient responses combining wall thinning locations and lift-off distances were plotted.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.302-307
Magnetic Sensor-Based Detection of Picoliter Volumes of Magnetic Nanoparticle Droplets in a Microfluidic Chip
We have designed, fabricated and tested an integrated microfluidic chip with a Planar Hall Effect (PHE) sensor. The sensor was constructed by sequentially sputtering Ta/NiFe/Cu/NiFe/IrMn/Ta onto glass. The microfluidic channel was fabricated with poly(dimethylsiloxane) (PDMS) using soft lithography. Magnetic nanoparticles suspended in hexadecane were used as ferrofluid, of which the saturation magnetisation was 3.4 emu/cc. Droplets of ferrofluid were generated in a T-junction of a microfluidic channel after hydrophilic modification of the PDMS. The size and interval of the droplets were regulated by pressure on the ferrofluid channel inlet. The PHE sensor detected the flowing droplets of ferrofluid, as expected from simulation results. The shape of the signal was dependent on both the distance of the magnetic droplet from the sensor and the droplet length. The sensor was able to detect a magnetic moment of 2 × 10−10 emu at a distance of 10 μm. This study provides an enhanced understanding of the magnetic parameters of ferrofluid in a microfluidic channel using a PHE sensor and will be used for a sample inlet module inside of integrated magnetic lab-on-a-chip systems for the analysis of biomolecules.
Journal of Magnetics, 31 Dec 2012, Vol.17 , No.4, pp.308-315
Enhancement of the Magnetic Flux in Metglas/PZT-Magnetoelectric Integrated 2D Geomagnetic Device
Experimental investigations of the magnetization, magnetostriction and magnetoelectric (ME) effects were performed on sandwich - type Metglas/PZT/Metglas laminate composites. The results have been analyzed by taking into account the demagnetization contribution. The study has pointed out that the magnetic flux concentration is strongly improved in piezomagnetic laminates with a narrower width leading to a significant enhancement of the ME effects. The piezomagnetic laminates with the optimal area dimension were integrated to form a 2-D geomagnetic device, which simultaneously can precisely detect the strength as well as inclination of the earth’s magnetic field. In this case, a magnetic field resolution of better than 10−4 Oe and an angle precision of ± 0.1o were determined. This simple and low-cost geomagnetic-field device is promising for various applications.