Search results for "Magnetic hysteresis"
showing 10 items of 51 documents
Magnetic and structural study of (Fe1−Co )62 Nb8B30 bulk amorphous alloys
2004
Abstract The electric and magnetic properties of rapidly quenched (Fe 1− x Co x ) 62 Nb 8 B 30 bulk metallic glasses were studied with x =0, 0.33 and 0.50. The Curie temperature in the amorphous state was found to be about 245 °C for the Co-free alloy, 290 °C for x =0.33 and 201 °C for x =0.50, while the crystallization temperature is varying within 15° only around 600 °C. The change in T C correlates with the change in Mossbauer parameters. An interesting flattening effect of annealing on the hysteresis loop was observed which increases with the Co content. The resistivity could not be improved above 152 μΩ cm, which limits the high frequency applications of these alloys.
Surface hysteresis curves of Fe(110) and Fe(100) crystals in ultrahigh vacuum — evidence of adsorbate influences
1992
Abstract We have investigated hysteresis curves of silicon-stabilized Fe(100) and Fe(110) crystals using Polarized Secondary Electron Emission (PSEE) for surface magnetization processes and Magneto-Optical Kerr Effect (MOKE) for bulk hysteresis curves. In particular, the influence of adsorbates (oxygen and sulphur) and surface roughness on the magnetization reversal has been studied. For surface hysteresis curves we found adsorbate-induced reductions of coercive force of up to 50%; the bulk hysteresis curves showed significantly smaller deviations. Similar changes were caused by surface disorder on an atomic scale induced by ion bombardment. The results agree qualitatively with a previous e…
Exploring the High-Temperature Frontier in Molecular Nanomagnets: From Lanthanides to Actinides.
2019
Molecular nanomagnets based on mononuclear metal complexes, also known as single-ion magnets (SIMs), are crossing challenging boundaries in molecular magnetism. From an experimental point of view, this class of magnetic molecules has expanded from lanthanoid complexes to both d-transition metal and actinoid complexes. From a theoretical point of view, more and more improved models have been developed, and we are now able not only to calculate the electronic structure of these systems on the basis of their molecular structures but also to unveil the role of vibrations in the magnetic relaxation processes, at least for lanthanoid and d-transition metal SIMs. This knowledge has allowed us to o…
Nucleation and Collapse of the Superconducting Phase in Type-I Superconducting Films
2005
The phase transition between the intermediate and normal states in type-I superconducting films is investigated using magneto-optical imaging. Magnetic hysteresis with different transition fields for collapse and nucleation of superconducting domains is found. This is accompanied by topological hysteresis characterized by the collapse of circular domains and the appearance of lamellar domains. Magnetic hysteresis is shown to arise from supercooled and superheated states. Domain-shape instability resulting from long-range magnetic interaction accounts well for topological hysteresis. Connection with similar effects in systems with long-range magnetic interactions is emphasized.
Magnetic Stochastic Resonance in systems described by Dynamic Preisach Model
2008
Stochastic resonance (SR) is generally considered as an enhancement of the system response for certain finite values of the noise strength. In particular the signal to noise ratio (SNR) and the signal amplification show a maximum as a function of the noise intensity. This effect has been experimentally observed in many physical systems and also in magnetic systems. However, as far as magnetic systems are concerned, the dynamic features of the systems have been neglected and it has been assumed that the typical relaxation time is negligible. However this is clearly a rough approximation. In order to clarify this relation, in this paper we numerically study magnetic stochastic resonance in se…
Magnetic phase transition and magnetic bistability in oxamato-based CoIICuII bimetallic MOF thin films
2019
Abstract Thin films of an anionic oxamato-bridged cobalt(II)–copper(II) 3D MOF have been growth at 120 °C in DMSO through a one-pot reaction from Co(NO3)2·6H2O and (Me4N)2[Cu(2,6-Et2pa)2]·6H2O (2,6-Et2pa = N-2,6-diethylphenyloxamate) over Si(111) surfaces functionalized with carboxylic acid terminating groups. These heterobimetallic CoII2CuII3 MOF thin films (2) of about ten nanometers thickness show a ferrimagnetically ordered phase below ca. 10 K with a relatively large magnetic hysteresis similar to that of the bulk material of formula (Me4N)2[Co2Cu3(2,6-Et2pa)6]·5H2O (1).
Elastic torsion effects in magnetic nanoparticle diblock-copolymer structures
2011
Magnetic properties of thin composite films, consisting of non-interacting polystyrene-coated γ-Fe(2)O(3) (maghemite) nanoparticles embedded into polystyrene-block-polyisoprene P(S-b-I) diblock-copolymer films are investigated. Different particle concentrations, ranging from 0.7 to 43 wt%, have been used. The magnetization measured as a function of external field and temperature shows typical features of anisotropic superparamagnets including a hysteresis at low temperatures and blocking phenomena. However, the data cannot be reconciled with the unmodified Stoner-Wohlfarth-Néel theory. Applying an appropriate generalization we find evidence for either an elastic torque being exerted on the …
Magnetic hysteresis in the microwave surface resistance of Nb samples in the critical state
2006
We discuss the hysteretic behavior of the field-induced variations of the microwave surface resistance in superconductors in the critical state. Measurements have been performed in a bulk sample of Nb and a powdered one at different values of the temperature. We discuss a model, based on the Coffey and Clem theory, in which we take into account the flux distribution inside the sample, due to the critical state. The experimental results are justified quantitatively in the framework of our model. We show that by fitting the experimental data it is possible to determine the value of the critical current density and its field dependence.
A dynamic model for hysteresis in magnetostrictive devices
2014
In this paper, a dynamic model for the description and design of hysteresis in magnetostrictive devices is presented. The model is based on Preisach theory and its dynamic extension. A procedure for determining the Preisach distribution function is given. This procedure is based on neural networks. The model is able to reconstruct both the magnetization relation and the field-strain relation. The model is validated through comparison and prediction of data collected from a typical Terfenol-D sample and a novel experimental technique dedicated to the validation of dynamic models is proposed.
Preparation, scaling behavior of activation energy, Hall effect, and flux-flow anisotropy of (Hg0.9Re0.1)Ba2CaCu2O6+δHTS thin films
2004
Abstract We have prepared fully textured (Hg0.9Re0.1)Ba2CaCu2O6+δ (HgRe-1212) thin films by pulsed laser deposition (PLD) and post-annealing. The films exhibit sharp superconducting transitions at Tc=124 K with transition width ΔTc≃2 K. Conditions for reproducible film preparation have been found. The resistive transitions have been investigated in magnetic fields up to 8 T (parallel to the c-axis) and 10 T (perpendicular to the c-axis). We have determined the activation energy of thermally activated flux-motion for both magnetic field orientations. The Hall resistivity (ρxy) of HgRe-1212 superconductor thin films has been measured in the ab-plane at 8 T. In the mixed state a power-law beha…