Showing papers on "Saturation (magnetic) published in 1997"
TL;DR: In this paper, the same Hamiltonian was used to explain magnetoresistance in structures with collinear magnetic alignments and the spin flip and non-flip scattering present in domain walls.
Abstract: Domain walls in ferromagnetic metals are known to be a source of resistance since the early experiments on iron whiskers. Recently it has been possible to identify this contribution from data on cobalt and nickel films which display stripe domains in which the current is driven normal to the domain walls. With the same Hamiltonian as used to explain giant magnetoresistance in structures with collinear magnetic alignments we have determined the spin flip, as well as nonflip, scattering present in domain walls. We calculate the resistivity in zero field, i.e., in the presence of striped domains, and at saturation to show the amount of magnetoresistance that is attributable to domain wall scattering.
374 citations
TL;DR: In this article, a model of the magnetization within NiFe2O4 nanoparticles consisting of ferrimagnetically aligned core spins and a spin-glass-like surface layer was proposed.
Abstract: Anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz et al.).5 These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mossbauer spectra indicated that all of the material was magnetically ordered. In the present study, we find that the lack of saturation in high fields is accompanied by irreversibility (i.e., hysteresis loops are open) up to 160 kOe. In addition, the particles exhibit time dependent magnetization in 70 kOe applied field. The high field irreversibility and the loop shift both vanish above 50 K. We propose a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin- glass-like surface layer. We find that qualitative features of this model are reproduced by a numerical calculation of the spin distribution. The implications of this model for possible macroscopic quantum tunneling in these materials are discussed.
270 citations
170 citations
TL;DR: In this article, a micromagnetic study of magnetic switching properties on sub-micron scale single layer and multilayer thin film elements is presented, and it is found that the switching field of these patterned film elements can strongly depend on these edge domain configurations.
Abstract: In this article, a micromagnetic study of magnetic switching properties on submicron scale single layer and multilayer thin film elements is presented. Even at deep submicron scale, there exist various edge domain configurations at the saturation remanent state. It is found that the switching field of these patterned film elements can strongly depend on these edge domain configurations. If the edge domains are not controlled, switching field of a patterned magnetic film element can vary significantly during repeated switching processes.
150 citations
TL;DR: In this article, the magnetization of spin-1/2 Heisenberg ladders with 3 legs is studied and plateaux with magnetization one third of the saturation value are shown to exist.
Abstract: Magnetization processes of spin-1/2 Heisenberg ladders are studied using strong-coupling expansions, numerical diagonalization of finite systems and a bosonization approach. We find that the magnetization exhibits plateaux as a function of the applied field at certain rational fractions of the saturation value. Our main focus are ladders with 3 legs where plateaux with magnetization one third of the saturation value are shown to exist.
117 citations
01 Jan 1997
TL;DR: In this paper, a survey of amorphous and nanocrystalline alloys for soft magnetic applications is presented, starting from their way of production and ranging over to the key factors which determine their properties.
Abstract: The article surveys amorphous and nanocrystalline alloys for soft magnetic applications. Both materials have much in common starting from their way of production and ranging over to the key factors which determine their properties. Thus, the magneto-crystalline anisotropy is randomly fluctuating on a scale much smaller than the domain wall width and, as a consequence, is averaged out by exchange interaction so that there is no anisotropy net effect on the magnetization process — the prerequisite for good soft magnetic behavior. Superior soft magnetic properties additionally require a low magnetostriction which is realized for amorphous Co-based alloys and, more recently, for nanocrystalline Fe-base alloys but at a significantly higher saturation induction and better thermal stability. Both materials reveal low losses up to several 100 kHz and their B-H loop can be tailored by magnetic field annealing according to the demands of application.
87 citations
TL;DR: In this paper, the magnetic viscosity and activation volume of elongated /spl alpha/Fe particles in alumite were investigated at room temperature for an anodized aluminum oxide film.
Abstract: Particle size effects on the magnetic viscosity and activation volume were studied at room temperature for elongated /spl alpha/-Fe particles in alumite (Fe nanowires in an anodized aluminum oxide film). Both magnetic viscosity and activation volume are strongly dependent on the particle diameter, but independent of the particle length. The magnetization reversal mechanism of elongated /spl alpha/-Fe particles in alumite films is discussed. The activation volume may represent the size of the magnetic switching unit propagating along the particle length during the non-uniform magnetization reversal.
79 citations
TL;DR: Results from the analyses of the tissue indicate the presence of ferromagnetic, fine-grained, magnetically interacting particles which, due primarily to magnetic properties, are thought to be magnetite and/or maghemite.
Abstract: Isothermal remanent magnetization (IRM) acquisition and alternating field (A.F.) demagnetization analyses were performed on human heart, spleen and liver samples resected from cadavers. The magnetic properties of the samples were measured both at 77K and at 273K. A.F. demagnetization was performed at 273K. Results from the analyses of the tissue indicate the presence of ferromagnetic, fine-grained, magnetically interacting particles which, due primarily to magnetic properties, are thought to be magnetite and/or maghemite. The presence of superparamagnetic particles can be inferred from the increase in saturation IRM values when measured at 77K compared with measurements at 273K and the decay of remanent magnetization upon warming from 77K. The concentration of magnetic material (assuming it is magnetite or maghemite) in the samples varies from 13.7 ng g-1 to 343 ng g-1, with the heart tissue generally having the highest concentration. The presence of magnetic material in these organs may have implications for the function of biogenic magnetite in the human body.
79 citations
TL;DR: In this article, the magnetization curves of melt-spun ribbons of NdFe-B with (BH ) max =16 MGOe have been measured in pulsed high magnetic fields up to 400 kOe to examine the applicability of the law of approach to ferromagnetic saturation to highly anisotropic uniaxial ferromagnets.
79 citations
TL;DR: In this article, the authors measured trapped field distributions by scanning a Hall probe on various rectangular YBCO bulk superconductors and studied the effects of field dependence of Jc bulk thickness and bulk size on the trapped field.
61 citations
TL;DR: In this paper, a multilayered structure containing a nominal Cu spacer layer thickness of 32 nm exhibits a large saturation magnetoresistance of more than 18% at room temperature.
Abstract: Reflection electron microscopy of electrodeposited Co, Cu/(111) Pt ultrathin layers and bilayers has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth Giant magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a (111) textured Co/Cu multilayered nanostructure, which is compositionally modulated over nanometer length scales with distinct ferromagnetic Co-Cu alloy and nonmagnetic Cu layers, prepared by electrodeposition under potential control in the presence of a very slight amount of CrO{sub 3} Such a multilayered structure containing a nominal Cu spacer layer thickness of 32 nm exhibits a large saturation magnetoresistance of more than 18% at room temperature Currently the development of new magnetic multilayered nanostructures has attracted considerable attention for potential applicability to magnetoresistive sensor devices
TL;DR: In this article, the advantage of the high etch selectivity between metals in a wet etching process to develop an optimized technique for engineering magnetic materials was used for fabricating mesoscopic Ni80Fe20 dots and wires with lateral dimensions down to 0.2 μm.
Abstract: We have used the advantage of the high etch selectivity between metals in a wet etching process to develop an optimized technique for engineering magnetic materials. This method is based on electron beam lithography and optimized pattern transfer by a combination of dry and wet etching. The technique has been used in fabricating mesoscopic Ni80Fe20 dots and wires with lateral dimensions down to 0.2 μm. We have used scanning electron microscopy to verify the lateral sizes and edge acuity of the structures. The magnetic properties were characterized using magneto-optic Kerr effect and magnetoresistance measurements. A marked increase in the coercive field and the saturation field is seen as the width of the wire is decreased. The magnetoresistance change (∂R) is found to increase significantly as the width of the wire is decreased.
TL;DR: A soft magnetic CoNiFeS film as a write head core material for the next generation was prepared by electrodeposition as mentioned in this paper, which consisted of fine minute crystal grains 5 to 10 nm in diameter.
Abstract: A soft magnetic CoNiFeS film as a write head core material for the next generation was prepared by electrodeposition. In this system, thiourea was used as an additive in the CoNiFe ternary alloy plating bath. The most suitable magnetic properties were obtained at the film composition of (Co 73 Ni 12 Fe 15 ) 99.1 S 0.9 [atomic percent (a/o)] with a high saturation magnetic flux density (B s ) of 1.7 T, a high resistivity (p) of 51 μΩ cm, and a low saturation magnetostriction (λ s ) of 4.4 x 10 -6 . The film consisted of fine minute crystal grains 5 to 10 nm in diameter. The S content of ca. 0.9 a/o is believed to be responsible for the formation of small crystal grains with low coercivity and high resistivity.
TL;DR: In this article, the properties of polycrystalline ferrites were studied for their saturation magnetisation n B, AC susceptibility χ and initial permeability μ i, which indicated that A-B and B-B superexchange interactions are comparable in strength.
TL;DR: In this paper, the relations among these curves and other useful magnetization curves (saturation initial curve and induced and remanent hysteretic magnetization curve) in order to compare coercivity and domain state parameters which can be derived from them are investigated.
Abstract: Isothermal magnetization curves, like hysteresis loops, initial curves, back field curves, acquisition curves and demagnetizing curves of isothermal remanent magnetization, are commonly used for rock magnetic purposes. In this study we investigate the relations among these curves and other useful magnetization curves (saturation initial curve and induced and remanent hysteretic magnetization curves) in order to compare coercivity and domain state parameters which can be derived from them. Most natural samples, especially sediments, are weakly magnetic and possess relatively stable Preisach functions. Their magnetization states can therefore be described by classical Preisach theory. This approach verifies well-known rules and establishes some formerly unreported relations between isothermal magnetization curves and parameters. It is possible to point out sets of mathematically independent isothermal magnetization curves and to state theoretical interrelations between dependent curves by simply inspecting Preisach diagrams. Furthermore, we define six elemental isothermal magnetization curves from a general partition scheme of the Preisach diagram. They can be easily obtained from common measurements and generate all above mentioned curves. The experimental applicability of our results is demonstrated for three (single-domain, pseudo-single-domain, multidomain) marine sediment samples. A physical rationale of the elemental curves reveals favorable properties for the investigation of interaction and domain state. As a spin-off from the general results, a new hysteresis-based procedure for the measurement of Hcr is presented. We also propose an apparently more robust hysteresis-derived domain state parameter and a generalized version of the well-known R parameter. All presented methods can be applied without actually measuring Preisach functions.
TL;DR: In this paper, the mixing effects induced by electronic energy deposition in nanoscale Fe/Si multilayers irradiated with swift heavy ions were investigated and a decrease in the mixing efficiency with electronic stopping power was reported; a threshold was found, under which iron environment modifications no longer occur.
Abstract: Mossbauer spectroscopy (57Fe) shows evidence for mixing effects induced by electronic energy deposition in nanoscale Fe/Si multilayers irradiated with swift heavy ions. A decrease in the mixing efficiency with electronic stopping power is reported; a threshold is found, under which iron environment modifications no longer occur. The kinetics of Fe–Si phase formation after irradiation suggests the existence of three regimes: (i) for high excitation levels, a magnetic amorphous phase is formed directly in the wake of the incoming ion and an almost complete mixing is reached at low fluence (1013 U/cm2); (ii) for low excitation levels, a paramagnetic Si-rich amorphous phase is favored at the interface while crystalline iron subsists at high fluences; (iii) for intermediate excitation levels, saturation effects are observed and the formation rate of both magnetic and paramagnetic phases points to direct mixing in the ion wake but with a reduced track length in comparison to U irradiation. The measured interfac...
TL;DR: In this article, the magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied.
Abstract: Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied. O2 is well known as a magnetic molecule with S=1. In the case of the low adsorption, temperature dependence of the susceptibility shows the Schottky-type broad peak and the high-field magnetization process has a step at around 34T with saturation moment of 2 μ B/O2. These results are interpreted by the dimer model of S=½ with an antiferromagnetic exchange interaction. Broadening of the step of magnetization with increasing the adsorption may be due to the inter-dimer interaction or the distribution of the intra-dimer exchange interaction. Linear magnetization process which is characteristic of one-dimensional Heisenberg antiferromagnet has not been observed even in the full pore region.
TL;DR: In this article, the in-plane saturation field is 60-70 kOe at 300 K, consistent with the bulk anisotropy field of 73kOe, and the spin reorientation transition at 135 K can also be clearly seen in the inplane and out-of-plane magnetization vs temperature data.
Abstract: Thin films of Nd{sub 2}Fe{sub 14}B with a c-axis orientation and bulk- like magnetic properties were grown with thickness as low as 300 {Angstrom}. They were grown on single-crystal MgO(100) wafers overcoated with epitaxial Mo(100) buffer layers. The 2-14-1 phase were crystallized either by sequential deposition or co-deposition of Fe, Nd, and B from pure elemental evaporation sources onto 600-700 C substrates. Structure of each film was characterized in-situ with RHEED and ex-situ with XRD. For the sequentially deposited films, the in-plane saturation field is 60-70 kOe at 300 K, consistent with the bulk anisotropy field of 73 kOe. The spin-reorientation transition at 135 K can also be clearly seen in the in-plane and out-of-plane magnetization vs temperature data. The out-of-plane coercivities range from 15-20 kOe at 20 K and 3-8 kOe at 300 K. Co-deposition results in a multiphase structure, with Nd{sub 2}Fe{sub 14}B now the minority phase. The multiphase structure results in reduced perpendicular anisotropy.
TL;DR: In this paper, a strong dependence of the two lowest order uniaxial anisotropies on Pt film thickness and temperature was observed and the possibility of an interfacial strain origin for the anisotropic due to lattice mismatch between the Co and Pt is discussed.
Abstract: We present results for perpendicular uniaxial anisotropies obtained using torque magnetometry and magnetic force microscopy on epitaxially grown Co/Pt multilayers. A strong dependence of the two lowest order uniaxial anisotropies on Pt film thickness and temperature were observed. The possibility of an interfacial strain origin for the anisotropies due to lattice mismatch between the Co and Pt is discussed. A surprising result is the appearance of magnetic orientations at oblique angles with respect to the film plane and the surface normal. These orientations are identified as “cone states” and found to exist in limited ranges of Pt film thickness and temperatures. The temperature dependence is very unusual and controlled through the behavior of the lowest order perpendicular uniaxial anisotropies. The magnetization process was also examined in terms of saturation fields and domain formation. Narrow stripe domains with periods less than 100 nm were observed in the demagnetized state using magnetic force m...
TL;DR: In this paper, the authors show that demagnetizing fields have a major role in determining the magnetic response of the arrays, which show high saturation fields and a coercivity which is lower than predicted by curling or uniform rotation models.
Abstract: Nanometer-sized Co arrays consisting of 200 nm or 20 nm diameter cylindrical islands, occupying a fractional surface area of 50 to 65%, have been synthesized by electrodeposition through the pores of suitable Al oxide templates. An increase in coercivity for 20 nm compared to 200 nm diameter Co island arrays is explained in terms of a transition to a single domain state. In this size range, demagnetizing fields have a major role in determining the magnetic response of the arrays, which show high saturation fields and a coercivity which is lower than predicted by curling or uniform rotation models. A high effective anisotropy is important in obtaining relatively high values of coercivity (up to 1700 Oe) in highly packed arrays.
TL;DR: In this paper, the magnetic properties after sintering of Ni0.34Zn0.60Fe2.06O4 from hydrothermal submicrometer-sized powders were evaluated.
TL;DR: In this article, a novel method for determining magnetic anisotropies from hysteresis loops is presented, where a magnetic field is applied perpendicularly to the sweep-field axis, causing the magnetization to rotate reversibly in a wide field range and still reach saturation at finite fields.
Abstract: A novel method for determining magnetic anisotropies from hysteresis loops is presented. While sweeping the loop, a magnetic field is applied perpendicularly to the sweep-field axis. This causes the magnetization to rotate reversibly in a wide field range and still reach saturation at finite fields. An example is given whereby surface and volume anisotropies are determined from magneto-optical Kerr effect loops in Co films grown on stepped Cu(001).
TL;DR: In this paper, the performances of two cylindrical reactors fed with microwave power through eight linear applicators and surrounded by either eight magnet bars or eight racetracks (magnetron-like magnetic structures) are measured and compared.
Abstract: In distributed electron cyclotron resonance plasma sources, the acceleration of electrons is produced by microwave electric fields, applied and distributed close to a multipolar magnetic field structure, providing along the magnets the condition for electron cyclotron resonance. The ensuing fast electrons are trapped in the multipolar magnetic field and drift along the magnets, hence the interest of a closed magnetic configuration to avoid losses at the boundaries of the confinement structure. The performances of two cylindrical reactors fed with microwave power through eight linear applicators and surrounded by either eight magnet bars or eight racetracks (magnetron-like magnetic structures) are measured and compared. In both cases plasma density saturates at the critical density, but in the case of the closed magnetic configuration the saturation is reached for a microwave input power a factor of ten lower than with the open magnetic configuration. This result confirms that the confinement effect of the multipolar magnetic field mainly applies to the fast electrons which generate the plasma.
TL;DR: In this paper, the soft magnetic properties of the nanocrystalline Fe-M-B (M=Zr,Nb) alloys, which exhibit a high saturation flux density (Bs) above 1.5 T as well as a high effective permeability (μe) above 30 000 at 1 kHz, were improved by adding small amounts of Cu and by optimizing the chemical composition.
Abstract: The soft magnetic properties of the nanocrystalline Fe–M–B (M=Zr,Nb) alloys, which exhibit a high saturation flux density (Bs) above 1.5 T as well as a high effective permeability (μe) above 30 000 at 1 kHz, were found to be improved by adding small amounts of Cu and by optimizing the chemical composition. The addition of Cu to the alloys decreases the bcc grain size. The excellent soft magnetic properties (a high μe of 100 000 at 1 kHz combined with a high Bs of 1.53 T) can be achieved in the region where small grain size, as well as nearly zero-magnetostriction are obtained, which is attained in the compositional range around Fe84Nb3.5Zr3.5B8Cu1. The soft magnetic properties can be further improved by low temperature annealing before the crystallization treatment, probably as a result of a decreased grain size distribution in the crystallized state. Consequently, the μe reaches the maximum value of 120 000 for the nanocrystalline Fe84Nb3.5Zr3.5B8Cu1 alloy.
TL;DR: In this paper, the authors investigated theoretically the effect of amplified spontaneous emission (ASE) on the spatial distribution of the carrier density and derived measures of the semiconductor optical amplifier performance, such as gain, saturation power and noise figure.
Abstract: The authors have investigated theoretically the effect of amplified spontaneous emission (ASE) on the spatial distribution of the carrier density. Measures of the semiconductor optical amplifier (SOA) performance, such as gain, saturation power and noise figure are derived. It is shown that the saturation due to the ASE strongly affects the SOA performance for device lengths > 500 µm. The results are compared with experimental data and found to be in good agreement.
TL;DR: In this paper, a distinct ESR (electron spin resonance) signal was found to overlap the E 1 ǫ center signal in natural quartz irradiated by γ-rays.
TL;DR: Recently, microwave ferrite devices with superconducting microstrip circuits have been demonstrated at a temperature of 77 K with virtually no electrical conduction losses as discussed by the authors, which has been the main regime for most device applications.
Abstract: At cryogenic temperatures magnetic properties of ferrites change significantly from their values at room temperature, which has been the main regime for most device applications. Recently, microwave ferrite devices with superconducting microstrip circuits have been demonstrated at a temperature of 77 K with virtually no electrical conduction losses. Conventional ferrimagnetic garnet and spinel compositions, however, are not generally optimized for low temperatures and may require chemical redesign if the full potential of these devices is to be realized. Saturation magnetizations increase according to the Brillouin–Weiss function dependence that is characteristic of all ferromagnetic materials. Increased magnetocrystalline anisotropy and magnetostriction can have large effects on hysteresis loop squareness and coercive fields that are essential for stable phase shift and efficient switching. Rare-earth impurities and other ions with short spin-lattice relaxation times can cause increased microwave losses....
Patent•
22 Oct 1997
TL;DR: A dipole permanent magnet structure with a rectangular gap about a longitudinal axis, in which tapered pole pieces form opposing sides of the rectangular gap to permit establishing a magnetic field in the gap, was proposed in this article.
Abstract: A dipole permanent magnet structure having a rectangular gap about a longitudinal axis, in which tapered pole pieces form opposing sides of the rectangular gap to permit establishing a magnetic field in the gap. Permanent magnets having a rectangular shape are coupled to the rear, or base, of each pole piece, and have a magnetic field oriented in the same direction as the pole pieces, perpendicular to longitudinal axis, thereby establishing a magnetic field between the pole pieces. Additional permanent magnets, including a pair of blocking magnets, are coupled to the aforementioned permanent magnets to form a magnetic circuit. The orientation of the magnetic field of each permanent magnet is generally aligned in the direction of the lines of flux in the magnetic circuit to maximize the flux density within the air gap created by formation of the permanent magnets. Moreover, the pair of blocking magnets each form an opposing side of the rectangular gap adjacent to the pole pieces to prevent fringing. The pole pieces and blocking magnets are tapered along the longitudinal axis such that the rectangular gap narrows from the proximate end to the distal end of the gap. The structure is thus capable of generating a magnetic field having a linear range of flux densities from a relatively low flux density to a flux density greater than the residual flux density of the magnet material. Indeed, the gap flux density is limited only by the saturation flux density of the pole pieces. Thus, the permanent magnets can be made of magnet material having high coercivity and high saturation magnetization level. An embodiment of the magnet structure is capable of generating a magnetic field in the air gap having a flux density range of 0.5 Tesla or less to 2.0 Tesla or more.
01 Mar 1997
TL;DR: In this article, a general procedure for inclusion of magnetising flux saturation in a d-q axis model of induction machines with two rotor windings is presented, which can be used to derive a model of a saturated induction machine for any selected set of state-space variables.
Abstract: Two models of induction machines with two rotor windings, that include magnetising flux saturation, are available at present: the first one is the current state-space model, where state-space variables are selected as d-q axis components of stator and both rotor currents; while in the second model state-space variables are d-q axis components of stator and both rotor flux linkages. The paper presents a general procedure for inclusion of magnetising flux saturation in a d-q axis model of induction machines with two rotor windings. Using the procedure, it becomes possible to derive a model of a saturated induction machine with two rotor windings for any selected set of state-space variables. The approach to magnetising flux saturation modelling relies on the concept of 'generalised flux space vector', which has recently been introduced for single-cage induction machines. Several characteristic models of a saturated induction machine, derived by applying the concept of the generalised flux space vector, are presented in detail. In order to verify the models, an extensive simulation study of the double-cage induction generator self-excitation process is performed, accompanied by the corresponding experimental investigation. The main results of the study are included. Finally, advantages of some of the novel models over the existing ones and possible applications are addressed.
TL;DR: The synthesis and magnetic properties of single-phase compounds have been investigated in this article, where the main phase of the Laves structure can still be observed up to x = 0.8.
Abstract: The synthesis and magnetic properties of have been investigated. The formation of is found to depend strongly on annealing temperature. Pure single-phase compound can be synthesized at ambient pressure when . The main phase of the Laves structure can still be observed up to x = 0.8. The study of crystalline parameters, magnetic moments and Mossbauer spectra for single-phase is performed. Curie temperature and local Fe magnetic moment increase with the increasing Pr concentration. Extrapolating the trends the spontaneous magnetization and anisotropy constant of are 4.98 and at 1.5 K, respectively. Magnetostriction increases with increasing x and the largest saturation magnetostriction, 200 ppm, is observed for x = 0.5. With the increase of Pr concentration, lattice parameter and spontaneous magnetization anomalies exist in a specific range 0.2 < x < 0.5 that can be attributed to the change of Ce ion valence toward tetravalent.