Search results for "Demagnetizing field"
showing 10 items of 28 documents
Magnetic resonance study of bulk and thin film EuTiO3
2017
Magnetic resonance spectra of EuTiO3 in both bulk and thin film form were taken at temperatures from 3-350 K and microwave frequencies from 9.2-9.8 and 34 GHz. In the paramagnetic phase, magnetic resonance spectra are determined by magnetic dipole and exchange interactions between Eu2+ spins. In the film, a large contribution arises from the demagnetization field. From detailed analysis of the linewidth and its temperature dependence, the parameters of spin-spin interactions were determined: the exchange frequency is 15-15.5 GHz and the estimated critical exponent of the spin correlation length is ~ 0.5. In the bulk samples, the spectra exhibited a distinct minimum in the linewidth at the N…
Orientational dynamics of colloidal ribbons self-assembled from microscopic magnetic ellipsoids
2016
We combine experiments and theory to investigate the orientational dynamics of dipolar ellipsoids, which self-assemble into elongated ribbon-like structures due to the presence of a permanent magnetic moment, perpendicular to the long axis in each particle. Monodisperse hematite ellipsoids are synthesized via the sol-gel technique and arrange into ribbons in the presence of static or time-dependent magnetic fields. We find that under an oscillating field, the ribbons reorient perpendicular to the field direction, in contrast with the behaviour observed under a static field. This observation is explained theoretically by treating a chain of interacting ellipsoids as a single particle with or…
Temperature Dependence of Irradiation-Induced Magnetic Flux Loss in Nd 2 Fe 14 B Permanent Magnets
1990
Nd2Fe14B permanent magnets were irradiated with 20 MeV protons at 300 K and at 15 K, and the flux loss was measured as a function of the irradiation dose. The results show that at 15 K the Nd2Fe14B magnets can withstand particle radiation at least 1000 times more than at room temperature.
Domain wall induced modulation of low field H-T phase diagram in patterned superconductor-ferromagnet stripes
2019
We present a systematic study of the magnetic domain wall induced modulation of superconducting transition temperature (Tc) in Nb/Ni bilayer stripes. By varying the thickness of the Ni layer from 20 nm to 100 nm we have been able to measure the low field Tc-H phase diagram spanning the Neel domain wall and Bloch domain wall range of thicknesses. Micromagnetic simulations and magnetic force microscopy measurements confirmed a stronger out-of-plane stray field in the Bloch domain walls compared to the Neel walls. A suppression in Tc was observed in the magnetization reversal region of the Ni film, the magnitude of which followed linearly to the strength of the out-of-plane stray field due to …
Ni61Mössbauer study of the hyperfine magnetic field near the Ni surface
1987
$^{61}\mathrm{Ni}$ M\"ossbauer measurements have been performed at 4.2 K on spherical Ni particles covered with a protective layer of SiO, with average diameter of 500 and 50 \AA{}. The hyperfine magnetic field at $^{61}\mathrm{Ni}$ nuclei for 500-\AA{} particles has been found to be 78.3(4) kOe, compared with the field for Ni foil of 75.0(2) kOe. The small difference is due to the demagnetization and dipolar fields in 500-\AA{} particles. The spectrum of 50-\AA{} particles has a surface component with the corresponding value of the hyperfine magnetic field of 40.3(5.4) kOe. This strongly indicates that, in accordance with recent theoretical studies, there is a decrease of the hyperfine mag…
Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy
2010
By example of a Permalloy particle (40 × 40 μm(2) size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cau…
Detection and Discrimination of Inter-Turn Short Circuit and Demagnetization Faults in PMSMs Based on Structural Analysis
2021
This paper presents a fault diagnosis method based on structural analysis of permanent magnet synchronous motors (PMSMs), focusing on detecting and discriminating two of the most common faults in PMSMs, namely demagnetization and inter-turn short circuit faults. The structural analysis technique uses the dynamic mathematical model of the PMSM in matrix form to evaluate the system’s structural model. After obtaining the analytical redundancy using the over-determined part of the system, it is divided into redundant testable sub-models. Four structured residuals are designed to detect and isolate the investigated faults, which are applied to the system in different time intervals. Finally, th…
Magnetic field and dielectric environment effects on an exciton trapped by an ionized donor in a spherical quantum dot
2017
Abstract Magnetic field and host dielectric environment effects on the binding energy of an exciton trapped by an ionized donor in spherical quantum dot are investigated. In the framework of the effective mass approximation and by using a variational method, the calculations have been performed by developing a robust ten-terms wave function taking into account the different inter-particles correlations and the distortion of symmetry induced by the orientation of the applied magnetic field. The binding and the localization energies are determined as functions of dot size and magnetic field strength. It appears that the variation of magnetic shift obeys a quadratic law for low magnetic fields…
The magnetic shielding for the neutron decay spectrometer aSPECT
2014
Abstract Many experiments in nuclear and neutron physics are confronted with the problem that they use a superconducting magnetic spectrometer which potentially affects other experiments by their stray magnetic field. The retardation spectrometer a SPECT consists, inter alia, of a superconducting magnet system that produces a strong longitudinal magnetic field of up to 6.2 T. In order not to disturb other experiments in the vicinity of a SPECT, we had to develop a magnetic field return yoke for the magnet system. While the return yoke must reduce the stray magnetic field, the internal magnetic field and its homogeneity should not be affected. As in many cases, the magnetic shielding for a S…
Influence of magnetic field on cooling by normal-insulator–superconductor junctions
2000
Cooling by normal-insulator–superconductor junctions in external magnetic field has been studied experimentally. For all orientations of magnetic field the cooling performance correlates with the magnetic field dependent superconducting energy gap Δ(H). In perpendicular orientation of magnetic field with respect to the sample plane, additional degradation of the cooling power originates from scattering of nonequilibrium quasiparticles in the superconductor on magnetic vortices. The effect is hysteretic and its magnitude depends on the shape of the superconducting probes.