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Showing papers on "Single domain published in 1993"


Journal ArticleDOI
TL;DR: In this paper, a combination of room temperature coercivity analysis and low temperature remanence measurements provided a characteristic magnetic signature for intact chains of single domain (SD) particles of magnetite from magnetotactic and dissimilatory iron-reducing bacteria.

430 citations


Journal ArticleDOI
TL;DR: In this paper, the concept of critical thickness, hc, for domain formation is developed for a single twin band in which the c axis of the tetragonal domains is either related by a 90° rotation about an axis in the plane of the film or by a normal about the surface normal, and the critical thickness depends only on the relative coherency strain between the substrate and film and the ratio of the domain wall energy to the stored elastic energy.
Abstract: Twin related domain formation is examined as a strain relaxation mechanism for a heteroepitaxial tetragonal film on a cubic substrate. Elastic relaxations are calculated for a single twin band in which the c axis of the tetragonal domains is either related by a 90° rotation about an axis in the plane of the film or by a 90° rotation about the surface normal. In all cases, the strain energy change is evaluated for both the film and the substrate. A domain pattern map is developed that predicts single domain and multiple domain fields depending on the relative misfit strains and domain wall energy. The concept of a critical thickness, hc, for domain formation is developed. For cases in which the c axis is rotated 90° about an axis in the plane of the film, the critical thickness depends only on the relative coherency strain between the substrate and film and the ratio of the domain wall energy to the stored elastic energy. For the case of a pattern consisting of energetically equivalent domains with the c a...

205 citations


Journal ArticleDOI
TL;DR: In this paper, a method is proposed to study the possible contribution of remanent magnetization to a particular anomaly, by comparing two functions that are calculated directly from the observations: (1) the amplitude of the analytic signal, and (2) the horizontal gradient of pseudogravity.
Abstract: Remanent magnetization can have a significant influence on the shape of magnetic anomalies in areas that are generally characterized by induced magnetization. Since modeling of magnetic anomalies is nonunique, additional constraints on the direction of magnetization are useful. A method is proposed here to study the possible contribution of remanent magnetization to a particular anomaly, by comparing two functions that are calculated directly from the observations: (1) the amplitude of the analytic signal, and (2) the horizontal gradient of pseudogravity. From the amplitude and relative position of maxima in these derived quantities, we infer the deviation of the magnetization direction from that of the ambient field. The approach is applied to the magnetic anomaly in the center of the Manicouagan impact structure (Canada). Our results, based only on the magnetic anomaly observations, are in close agreement with constraints on the direction of remanent magnetization from rock samples.

173 citations


Journal ArticleDOI
TL;DR: Elongated ferromagnetic single-domain particles are believed to exhibit a high stability of their remanent magnetization but here it is shown that for elongated particles thermal fluctuations lower the coercivity much more drastically than predicted by current theories.
Abstract: Elongated ferromagnetic single-domain particles are believed to exhibit a high stability of their remanent magnetization However, here it is shown that for elongated particles thermal fluctuations lower the coercivity much more drastically than predicted by current theories The rate for magnetization reversal is calculated for a classical model of a ferromagnet that allows for a spatially nonuniform magnetization distribution along the sample The prefactor of the Arrhenius factor is explicitly evaluated and analytical results are obtained in the experimentally important limit of external magnetic fields close to the anisotropy field and for moderate damping

125 citations


Journal ArticleDOI
TL;DR: In this paper, the magnetomechanical hysteresis model of Sablik and Jiles is extended to treat magnetic properties in the case of noncoaxial stress and magnetic field in an isotropic, polycrystalline medium.
Abstract: Although descriptions of the effect of stress on spontaneous magnetization within a single domain already exist, there remains no adequate mathematical model for the effects of noncoaxial magnetic field and stress on bulk magnetization in a multidomained specimen. This article addresses the problem and provides a phenomenological theory that applies to the case of bulk isotropic materials. The magnetomechanical hysteresis model of Sablik and Jiles is thus extended to treat magnetic properties in the case of noncoaxial stress and magnetic field in an isotropic, polycrystalline medium. In the modeling, noncollinearity between magnetization and magnetic field is taken into account. The effect of roll‐axis anisotropy is also considered. Both magnetic and magnetostrictive hysteresis are describable by the extended model. Emphasis in this article is on describing properties like coercivity, remanence, hysteresis loss, maximum flux density, and maximum differential permeability as a function of stress for various angular orientations between field and stress axis. The model predictions are compared with experimental results.

89 citations


Journal ArticleDOI
TL;DR: In this paper, the nucleation and growth of 123 from the melt via a peritectic reaction into domains of aligned platelets is studied and the microstructure of well-formed domains indicates that there is no orientation difference between adjacent platelets within a domain.
Abstract: Nucleation and growth of 123 from the melt via a peritectic reaction into domains of aligned platelets is studied. Analysis of the microstructure of well-formed domains indicates that there is no orientation difference between adjacent platelets within a domain, suggesting that a domain grows from a single nucleus. The platelet boundaries are found to be filled-in with secondary phases that correspond to the liquid phase at high temperature, suggesting that constitutional supercooling effects may be operative. Samples quenched from temperatures considerably below the peritectic temperature contain only a few crystals, indicating the presence of a large nucleation barrier. The above observations, coupled with extensive microstructural examination of quenched solid-liquid interfaces, suggest that the 211 size, distribution and volume fraction not only control the growth rate of 123 along the fast growth ab -plane (by supply of yttrium), but also the growth rate along the slow growth c -direction since the nucleation barrier is reduced at 211/123 intersections. At high cooling rates there is a distinct change in the nucleation and growth processes. Structures characteristic of sympathetic or autonucleation and spherulitic growth are observed. These structures are distinct from the single crystal nature of well-formed domains. The growth mechanism which results in the formation of 123 domains and the final microstructure within a single domain, also explains the observed non-weak-link characteristics for current flow along the a , b - and c -directions, as determined by direct transport and magnetization measurements.

73 citations


Journal ArticleDOI
TL;DR: In this article, a comprehensive study of the magnetic properties of noninteracting single-domain particles with cubic magnetocrystalline anisotropy is presented, where numerical calculations extend the zero-temperature predictions of Joffe and Heuberger and enable the effects of thermally activated magnetization reversal on the hysteresis loop at finite temperatures.
Abstract: A comprehensive study of the magnetic properties of non-interacting single-domain particles with cubic magnetocrystalline anisotropy is presented. These numerical calculations extend the zero-temperature predictions of Joffe and Heuberger and enable the effects of thermally activated magnetization reversal on the hysteresis loop at finite temperatures to be determined. Variations in particle size distribution are also considered. Calculations indicate a reduction in the intrinsic coercivity as the mean particle diameter is reduced and an increase in coercivity for small particle diameter systems as the standard deviation of the size distribution is increased.

66 citations


Journal Article
TL;DR: In this paper, a transition from a plating configuration to a surface droplet configuration is predicted using cell-dynamical simulations, assuming that the surface domain thickness is not too much order near the boundary induced by the surface forces at early times.
Abstract: Domain growth in a binary mixture, after a quench through its demixing critical point, near a boundary that attracts one of the components, is discussed. When mean-field theory is valid for equilibrium properties, a single domain may form at the substrate for much weaker surface interactions than those necessary for complete wetting in equilibrium. Prediction of a transition from such a «plating» configuration to «surface droplets» is verified using cell-dynamical simulations. At later times, if diffusion is the dominant transport process, simulations show the surface domain thickness to increase according to the bulk domain growth law R=t 1/3 -if there is not too much order near the boundary induced by the surface forces at early times

61 citations


Journal ArticleDOI
TL;DR: In this article, the authors present experimental results on the magnetic relaxation in different systems (single domain particles, magnetic grains, and random magnets) and demonstrate the existence of two relaxation regimes.
Abstract: In this article we present experimental results on the magnetic relaxation in different systems (single domain particles, magnetic grains, and random magnets). The existence of two relaxation regimes is demonstrated. At high temperatures, the magnetic viscosity S≡1/M0∂M/∂ ln(t) is proportional to temperature in accordance with theoretical expectation for thermally activated processes. At low temperatures, the viscosity is independent of temperature, providing evidence to quantum tunneling of magnetization. Qualitative agreement between theory and experiment is found.

58 citations


Journal ArticleDOI
TL;DR: In this paper, the reversible susceptibility, the total susceptibility, and the temperature dependence of the coercive field of a magnetically isotropic nanocrystalline Sm•Fe•N magnet have been measured up to a field strength of 6.4 MA/m.
Abstract: Sm‐Fe‐N permanent magnets have been prepared by mechanical alloying of Sm and Fe powder and subsequently treating the material in a two‐step process. Measurements of the minor hysteresis loops and of the initial magnetization curve were performed at room temperature. The reversible susceptibility (χrev), the total susceptibility (χtot) of the initial magnetization curve and of the demagnetization curve, and the temperature dependence of the coercive field (Hc) of a magnetically isotropic nanocrystalline Sm‐Fe‐N magnet have been measured up to a field strength of 6.4 MA/m. The anisotropy constants, K1 and K2, of Sm2Fe17Nx were deduced from the crystalline electric field calculation in the temperature range from 0 to 500 K. The critical diameter of single domain Sm‐Fe‐N particles was calculated to be 320 nm at room temperature. This leads to the conclusion that mechanically alloyed Sm‐Fe‐N is composed of single‐domain particles. The temperature dependence of the coercive field of Sm‐Fe‐N has been analyzed w...

53 citations


Journal ArticleDOI
TL;DR: In this paper, the development of tweed texture during annealing was investigated using computer simulation and the model is a two-dimensional one corresponding to an oxygen deficit layer of a higher temperature superconducting crystal of YBa2Cu3O7.
Abstract: The development of tweed texture during annealing is investigated using computer simulation. The model is a two-dimensional one corresponding to an oxygen deficit layer of a higher temperature superconducting crystal of YBa2Cu3O7. The model may be taken as generic, including three dimensional systems, with regard to its semiquantitative behaviour and shows a ferroelastic phase transition due to local strains connected with the oxygen ordering. After quenching from a high temperature, a pronounced {1,1} micro-twinning appears. It starts from a fine irregular tweed-like pattern, with the spacing between domain walls becoming more regular while coarsening during the anneal. Annealing at lower temperatures, but not near Tc, produces an intermediate stripe structure before annealing to a single domain. From the rate at which the distance between domain walls increases, a temperature-time-transition (T-T-T) diagram has been constructed which shows strong similarities to those obtained from experiments. So do the other features mentioned.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional micromagnetic model is used to obtain magnetic domain structures for cubic particles of magnetite with sides 1 μm or less, and it is shown that complex submicron structures evolve continuously with increasing particle size into recognizable classical domain structures.
Abstract: A two-dimensional micromagnetic model is used to obtain magnetic domain structures for cubic particles of magnetite with sides 1 μm or less. We show that complex submicron structures evolve continuously with increasing particle size into recognizable classical domain structures. Two such sequences of equilibrium states are seen. The lowest energy state for particle sizes above 0.06 μm is the “vortex” state (already seen in three-dimensional models). Another state is seen in larger particles which has angles between walls of 90°, 125°, and 145°, agreeing with domain observations of magnetite. These are usually called 71°, 109°, and 180° walls, based on the assumption that the domain moments are in the easy ([111]) directions, but we find that the domains are actually magnetized in the [100] and [110] directions. Because both states eventually become single domain in sufficiently small particles, there is no critical single domain size in a conventional sense, but there is a rapid decrease in normalized remanence over the size range 0.06 – 0.18 μm. Bloch-like and Neel-like walls are seen, but strong surface fields are only found over the Bloch-like walls. Depending on the geometry of the particle observed, one may see only a partial expression of closure domains in domain observations.

Patent
06 Jul 1993
TL;DR: A thin film magnetic head includes an upper magnetic pole film (7) and a lower magnetic pole films (2) laminated one on another through a magnetic gap layer (3).
Abstract: A thin film magnetic head includes an upper magnetic pole film (7) and a lower magnetic pole film (2) laminated one on another through a magnetic gap layer (3). The upper and lower magnetic pole films are multilayer thin films, respectively, each of which is composed of a plurality of magnetic thin film layers (21) and a plurality of non-magnetic thin film layers (22), alternately laminated one on another. If there are an even number of magnetic layers (21), they are of equal thickness. If however there are an odd number of magnetic layers. the thickness of each layer is calculated from the thicknesses of adjacent layers. The magnetic layers (21) may consist of a Co-containing amorphous alloy with Hf,Ta and Pd, The non-magnetic layers (22) may be SIN, SiO2 or Al2 O3. The magnetic pole films (2) and (7) have single domain structures, respectively, and the use of such magnetic pole films realizes a thin film magnetic head having high permeability at high frequencies and improved high frequency characteristics and attains high recording density.

Journal ArticleDOI
TL;DR: Neutron-depolarization and small-angle neutron-scattering (SANS) measurements were performed to obtain some magnetic information in various spatial scales on the reentrant-spin-glass state of Ni 77 Mn 23.
Abstract: Neutron-depolarization and small-angle neutron-scattering (SANS) measurements were performed to obtain some magnetic information in various spatial scales on the reentrant-spin-glass state of ${\mathrm{Ni}}_{77}$${\mathrm{Mn}}_{23}$. The wavelength-dependent neutron polarization in the magnetic fields offered some information about the temperature-dependent magnetic-domain-wall motion and the magnetization rotation in domains, i.e., (1) the domain-wall motion decreases with decreasing temperature, and (2) the magnetization in each domain shows a rigid rotation at low temperatures and a dissipative nature at higher temperatures when applying a magnetic field. The SANS intensity peak at a finite momentum transfer q that appeared in the magnetic fields indicates the formation of a modulated structure of transverse spin components in the domain. The spin structure was interpreted as vortexlike so as to obtain a consistent interpretation about the low-temperature behavior of the period of oscillatory neutron polarization as a function of wavelength. The field and temperature dependences of SANS intensity were well interpreted in terms of the vortex spin structure. Finally, we had a picture that the magnetization process in the reentrant state is characterized by the nature of the domain-wall motion and the magnetization rotation that strongly correlates with the spin-modulated structure.

Journal ArticleDOI
TL;DR: In this article, a vertical Bridgman method was used for the growth of monolithic YBa 2 Cu 3 O 7 superconductors with a very homogeneous distribution of micronic or submicronic precipitates.

Journal ArticleDOI
Robert K. Adair1
TL;DR: The possibility that weak ELF magnetic fields may cause biological effects in humans by the interaction of the field with magnetosomes must be considered.
Abstract: The effects of 60 Hz magnetic fields of 5 [mu]T (50 mG) or less on biological structures holding magnetite (Fe[sub 3]0[sub 4]) are shown to be much smaller than that from thermal agitation; hence such interactions cannot be expected to be biologically significant. Various species have been shown to manufacture magnetite, which is used in some cases in conjunction with the earth's magnetic field to determine direction ([Frankel, 1986; Kirschvink and Kobayashi-Kirschvink, 1991].) This magnetite is usually found in sets of single domain grains, about 500[angstrom] in diameter, where all grains are magnetized in the same direction. Typically, such grains are enclosed by a membrane and are called magnetosomes. Hence, the possibility that weak ELF magnetic fields may cause biological effects in humans by the interaction of the field with magnetosomes must be considered.

Journal ArticleDOI
TL;DR: In this paper, exact solutions for the longitudinal relaxation time T∥ and the complex susceptibility χ∥(ω) of a thermally agitated single domain ferromagnetic particle are presented for the simple uniaxial (Maier-Saupe) potential of the crystalline anisotropy considered by Brown.

Journal ArticleDOI
TL;DR: In this paper, the authors used neutron diffraction techniques to study the field dependence of the magnetic ordering of Cu spins in R2CuO4 (R=Nd,Sm) in order to distinguish between the proposed collinear and noncollinear spin structures.
Abstract: We have used neutron diffraction techniques to study the field dependence of the magnetic ordering of Cu spins in R2CuO4 (R=Nd,Sm) in order to distinguish between the proposed collinear and noncollinear spin structures. In the proposed collinear spin structure, there are two separate domains with the spins either along the (110) or along the (110) directions, while in the noncollinear model there is a single domain with the alternate‐layer spins along the (100) and (010) directions, respectively. If a magnetic field is applied along the (110), strong hysteresis effects are anticipated for the collinear spin structure due to domain repopulation, while such effects are not expected for the noncollinear spin structure. Our field dependent data do not show any hysteresis effects associated with the pure Cu ordering, which strongly suggest that the noncollinear spin structure is correct for the magnetic spin configuration of the Cu spins in both compounds. Hysteresis effects in a field are observed in Sm2CuO...

Journal Article
TL;DR: In this paper, the relationship between magnetization reversal and microstructure is still poorly understood, and four types of magnetic characterization are used (temperature dependence of the coercive field, angular dependence of coercive fields, magnetic viscosity and the direct evaluation of dipolar fields).
Abstract: In permanent magnetic materials magnetization reversal does not take place by coherent and global rotation. No collective processes are involved when the energy barrier implicated in the reversal is of magnetocrystalline nature acting at the atomic level. The mechanism by which magnetization reversal occurs involves several events which are inherently linked to the presence of defects. These events, nucleation, propagation and pinning - depinning of a domain wall, are strongly linked to the microstructure. The liaison between magnetization reversal mechanisms and microstructure is still poorly understood. Four types of magnetic characterization are used (temperature dependence of the coercive field, angular dependence of the coercive field, magnetic viscosity and the direct evaluation of dipolar fields) where the analysis may or may not be based on a model

Journal ArticleDOI
TL;DR: In this paper, the change of the easy magnetization direction from easy plane to easy axis of the primary compound Sm2Fe17 by absorbing nitrogen is directly observed by the domain pattern.
Abstract: In the present work the change of the easy magnetization direction from easy plane to easy axis of the primary compound Sm2Fe17 by absorbing nitrogen is directly observed by the domain pattern. The intrinsic magnetic parameters of nitrided Sm2Fe17Nx such as domain wall energy γ, average exchange constant A, domain wall width δB, as well as the critical diameter of single domain particles Dc are estimated. The domain behavior of Sm2Fe17Nx under the applied external field is also investigated. Our results indicate that the nuclei initially occurring in the bulk of the grain are weakly pinned and that the coercivity of the material is dominated by the nucleation occurring at the surface of the grain, which is relative larger than the pinning field within the grain. In the Sm2Fe17N2.15 compound, a three-dimensional domain pattern is observed, which directly gives an experimental support of Goodenough's assumption that the walls are slabs in the main body and zigzag undulatory walls with a decreasing amplitude of undulations with increasing distance from the surface.

Proceedings ArticleDOI
04 Oct 1993
TL;DR: In this paper, the construction of the magnetic encoder with a magnetoresistance sensor and a multi-pole magnetic drum is described, and a rotatory magnetization system has been developed to magnetize the magnet encoder.
Abstract: The construction of the magnetic encoder with a magnetoresistance sensor and a multi-pole magnetic drum is described. A rotatory magnetization system has been developed to magnetize the magnetic encoder. It is found that the sine-PWM magnetization is superior over the single-pulse magnetization when high resolution is needed.

Journal ArticleDOI
TL;DR: In this paper, the effects of magnetic screening by soft walls on alternating field stability of multi-domain (MD) grains have been investigated and it is shown that due to screening, AF stabilities of MD grains are usually significantly higher than their microcoercivities, the only exception being for two-domain grains, where there is no screening.
Abstract: Both analytical arid numerical models are developed to investigate the effects on alternating field (AF) stability of both microcoercivity associated with pinned walls and magnetic screening by soft walls in multi-domain (MD) grains. It is shown that due to screening, AF stabilities of remanence in MD grains are usually significantly higher than their microcoercivities, the only exception being for two-domain grains, in which there is no screening. One important implication is that hard “pseudo-single-domain” remanence observed in grains larger than single-domain size but with AF stabilities higher than the expected maximum microcoercivity associated with domain wall pinning may be simply due to the screening by soft walls in individual grains. Moreover, we predict that MD grains containing a small number of defects do not necessarily show a low AF stability, for the reduction in the AF stability by a small microcoercivity in this case may be outweighed by a large screening due to a relatively large number of soft walls available in the grains. This prediction is supported by the experimental evidence that two types of magnetites (crushed and hydrothermally grown) with very different defect densities have similar values of median destructive field.

Journal ArticleDOI
TL;DR: In this article, a space charge field model was proposed to explain the mechanism of a ferroelectric domain inversion phenomenon in proton-exchanged LiTaO3 plates, and it was shown that the single-domain surface layers formed had spontaneous polarizations directed outward from the plate.
Abstract: A space charge field model to explain the mechanism of a ferroelectric domain inversion phenomenon in proton‐exchanged LiTaO3 has been proposed. This model predicts that single‐domain layers could be formed on both surfaces of a proton‐exchanged multidomain LiTaO3 plate without application of external electric fields. Experimental results demonstrating this prediction are reported. It is shown that the single‐domain surface layers formed had spontaneous polarizations directed outward from the plate. This suggests the existence of a space charge field near the surfaces.

Journal ArticleDOI
TL;DR: In this paper, a comprehensive study of the remanence curve properties of an assembly of noninteracting single-domain particles with cubic magnetocrystalline anisotropy has been performed.
Abstract: For pt.I see ibid., vol.5, p.2779-92 (1993). A comprehensive study of the remanence curve properties of an assembly of noninteracting single-domain particles with cubic magnetocrystalline anisotropy has been performed. The theoretical calculations presented represent an extension of the zero-temperature analysis of Joffe and Heuberger to include the effects of thermally activated magnetization reversal and particle size distribution. The numerical validity of these computations is completed through the analysis of interaction-sensitive Henkel plots, which confirm the non-interacting nature of the independently calculated remanence curves. The model system shows behaviour with intuition and analogous to similar models for the uniaxial case, with the exception of the expected increase in maximum remanence and decrease in energy barrier, i.e. remanence coercivity.

Journal ArticleDOI
TL;DR: In this article, a scaling analysis of the ferromagnetic transition in granular magnetic solids was performed, and the Curie temperature and critical exponents of the critical exponent were obtained.
Abstract: We have produced granular Ni–Al2O3 solids by magnetron sputtering, and the entire composition range has been studied. The percolation threshold (pc) has been identified to be near 55 percent Ni by volume, in agreement with other granular metal systems. Below pc, the samples display typical single domain magnetic behaviors, including superparamagnetism and enhanced coercivity. However, above percolation the samples display ferromagnetic transitions which differ substantially from the transition in pure Ni. We have performed a scaling analysis of the ferromagnetic transition in several such materials, and have obtained values of the Curie temperatures and the critical exponents. These are the first such analyses of the ferromagnetic‐paramagnetic transition in granular magnetic solids. We have observed a depression of the Curie temperature as the Al2O3 content of the samples is increased, as well as a substantial variation of the critical exponents. The variation of Tc may be understood in terms of finite si...

Journal ArticleDOI
TL;DR: In this article, the orientation distribution of magnetic particle suspensions subjected to external magnetic and hydrodynamic fields is investigated for the manufacture of particulate recording media, and a scaling theory for uniaxial single domain systems is presented, which qualitatively reproduces the observed φ, Hc and shape dependences of the order parameter deduced from the data.

Journal ArticleDOI
TL;DR: In this paper, the authors present a study of the magnetic relaxation of several ferrofluids composed of particles of about 40 A in diameter (Fe3O4FeC, CoFe2O4).
Abstract: We present a study of the magnetic relaxation of several ferrofluids composed of particles of about 40 A in diameter (Fe3O4FeC, CoFe2O4). Our key observation is a nonthermal character of the relaxation below 3 K for the CoFe2O4 ferrofluid and below 1 K for the FeC ferrofluid. The crossover temperature from thermal to nonthermal (quantum) regime is in accordance with theoretical suggestions of macroscopic quantum tunneling of magnetization in single domain particles.

Journal ArticleDOI
TL;DR: Within a model of the coherent rotation, underdamped dynamics of magnetization in single-domain ferromagnetic particles are assumed and the prefactor f 0 (h) of the thermal decay rate as a function of the applied field h is calculated.
Abstract: Within a model of the coherent rotation, we assume underdamped dynamics of magnetization in single-domain ferromagnetic particles and calculate the prefactor f 0 (h) of the thermal decay rate as a function of the applied field h. Four different models of dissipative coupling are considered. As opposed to the previously reported temperature dependence of the prefactor, the field dependence is remarkably independent of the chosen coupling mode. The prefactor f 0 (h) drops off sharply as h approaches the nucleation field and significantly enhances the coercivity whose model calculation, together with that of the switching-field distribution, is carried out

Journal ArticleDOI
01 Apr 1993
TL;DR: In this article, the magnetic susceptibility change in heterogeneous magnetic materials as a function of the magnetic matter characteristics (grain size, chemical composition, concentration) and also of the sample shape is studied.
Abstract: The magnetic susceptibility change in heterogeneous magnetic materials as a function of the magnetic matter characteristics (grain size, chemical composition, concentration) and also of the sample shape is studied. Techniques for measuring weak susceptibilities are described. They are used to show the existence of macroscopic demagnetizing fields in rod specimens beyond a certain volume of magnetic matter. >

Journal ArticleDOI
TL;DR: In this paper, the nucleation as well as the pinning fields in Sm2Fe17Nx Sn-bonded material are analyzed based on the well established micromagnetic theory.
Abstract: In the present paper the nucleation as well as the pinning fields in Sm2Fe17Nx Sn-bonded material are analysed based on the well established micromagnetic theory. The microstructural parameters derived from the measured temperature dependence of the coercive field indicate that the coercive field in Sm2Fe17Nx Sn-bonded material is dominated by the nucleation field occurring in the inhomogeneous area near the grain surface. The magnetic phase transition at the Curie temperature from the ferromagnetic to the paramagnetic state of the magnetically soft phase Sm2Fe17 existing in Sm2Fe17Nx magnets leads to a decrease of the effective demagnetization factor. Furthermore the temperature dependence of the domain wall energy γ, the average exchange constant A, the domain wall width δB, as well as the critical diameter of a single domain particle Dc.