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Deals with a study which analyzed the problem of how singular point detection in the magnetization curve is transformed in the case of a polycrystalline specimen. Examination of how the critical parameters of first-order magnetization processes were modified; Methodology of the study; Results and discussion.

Presents information on a study that examined the problem of singular point detection in the case of multidomain crystallites. Basis of the analysis of the magnetization curve of a polycrystalline material; Investigation of the effects on the peak of crystallites' shapes and angular distribution; Conclusions.

Cobalt/iron multilayers with different layer thickness were electron beam evaporated in ultrahigh vacuum, keeping constant both the number of layers and the Co/Fe thickness ratio. Structural and magnetic properties are thoroughly investigated with different techniques. The multilayers have clean and sharp interfaces. All samples show single-phase magnetic behavior in the temperature range of 5–300 K, due to the strong exchange coupling between the layers. The room temperature hysteresis loops present a sharp switching at a field of ∼8 kA/m, followed by a residual hysteresis extending up to saturation, at fields of several tens of kA/m. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study, which determined the orientation density of the tetragonal axes of the Nd[sub2]Fe[sub14]B crystallites in sintered neodymium-iron-boron magnets with different degrees of grain alignment. Methods used in the study; Description of the orientation density of an easy axis; Analysis of trial demagnetization curves.

Abstract: A thorough micromagnetic analysis of the exchange-spring problem is reported with special emphasis on multilayers constituted by hard–soft exchange-coupled phases. The developed one—dimensional micromagnetic model leads to a complete magnetic phase diagram in terms of layer thicknesses. Both perpendicular and parallel configurations are considered. The phase diagram provides information on the type of demagnetization processes and the critical fields at which nucleation and reversal take place, depending on the intrinsic properties of the chosen soft and hard materials. The model has been applied to a variety of hard magnetic phases (e.g., FePt, CoPt, SmCo and NdFeB), coupled to different soft materials (e.g., Fe, FeCo, FeRh or permalloy) both in the form of bilayers and multilayers. The most significant results will be highlighted. [Copyright &y& Elsevier]

Describes the use of a magnetic susceptometer in the field of nanoscale magnetic systems. Problems which limit experimental applications of thermomagnetic analysis (TMA); Alternating gradient instruments; Adopted design criteria.

A new type of high-sensitivity magnetic susceptometer is proposed. It utilises a long thin vibrating wire as a sample support, which is driven at resonance by an alternating field gradient, with no applied dc field. The gradient is generated by a tiny soft ferromagnetic rod close to the sample, The chosen configuration is particularly suitable to perform measurements on thin films and small samples in a wide temperature range (up to 1200 K). A realised prototype for high temperatures is described, with a few examples of measurements. An analysis of the moment sensitivity and considerations on the noise are given, with indications of the physical limits of the technique. A moment sensitivity of the order of 10/sup -11/ A/spl middot/m/sup 2///spl radic/Hz, with an alternating field of 100 A/m, is estimated for the present prototype. [ABSTRACT FROM PUBLISHER]

Abstract: The imaginary part of the second harmonic of the reversible parallel susceptibility (RPS) has been recently demonstrated to be a sensitive probe for determining the anisotropy fields in polycrystalline hard magnetic materials, by means of the singular point detection technique (SPD). A modified SPD theory is depicted here considering the presence of domain walls in the multi-domain crystallites, on the basis of Néel''s phase theory. Measurements performed on Ba-ferrite random powder show that the energy losses related to domain wall motion are likely at the origin of the observed effect. [Copyright &y& Elsevier]

Reversible and irreversible magnetization processes have been investigated in thin Ni sheets by means of flux-metric and alternating-gradient-force magnetometer techniques. Cold-rolled samples exhibit a rotation-dominated process at low fields, and the value of the associated susceptibility, related to the stress-induced and the magnetocrystalline anisotropies, can provide an estimate of the residual stress in the material. Reversible displacements of the domain walls come into play and combine with rotations in the annealed samples. A method is devised, by which domain-wall and rotational contributions to the reversible susceptibility can be singled out. The Rayleigh law always accounts for the behavior of hysteresis loops and losses at low fields, but rotations engender some peculiar evolution of the related parameters and their relationship with the coercive field. Magnetic softening by stress relief is assessed, as a whole, through Preisach analysis. It is found that the local stochastic coercive fields can be described by means of a Lorentzian distribution function, whose relative width is minimum in the cold-rolled material. By removing the internal stresses through recrystallization annealing, the contribution of grain boundaries and surface effects to coercivity is put in evidence, with the latter apparently posing the major restraints to domain-wall motion for grain sizes larger than the sheet thickness. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The switching process of electrodeposited Co-rich Co–Pt thin films with perpendicular magnetic anisotropy is investigated by out-of-plane angle-dependent hysteresis loop measurements. The switching field angular dependence is discussed in terms of basic reversal mechanisms. A model is proposed, based on a two-step switching process, to evaluate the variations of the intensity and orientation of the internal field as the modulus of external magnetic field is varied at each angle φ. Several experimentally observed salient features are well-understood, indicating that switching is due to inverse domain propagation. [Copyright &y& Elsevier]

Abstract: Co80Pt20 films of varying thicknesses have been prepared by electrodeposition on Cu seed layers. The films display perpendicular magnetic anisotropy and large coercivities. Soft/hard bilayers were subsequently obtained by sputter deposition of Ni80Fe20 layers. A thorough experimental analysis of the magnetization reversal is carried out in samples with different layer thicknesses by measuring the total susceptibility, the recoil initial susceptibility and the ac reversible susceptibility as a function of the applied field, allowing to discriminate between reversible and irreversible processes and to point out exchange-spring behaviour. [Copyright &y& Elsevier]

The magnetisation process has been investigated in thin Ni sheets by means of fluxmetric and alternating force techniques. As-rolled samples exhibit a rotation-dominated reversible magnetisation process, related to stress-induced and magnetocrystalline anisotropies. After annealing the rotations combine with substantial reversible displacements of the domain walls. It is always found that the transverse reversible susceptibility passes through a maximum at a field of the order of the anisotropy field. [Copyright &y& Elsevier]

We present a study of the magnetic properties and magnetization processes in hard Co-Pt (Pt∼20 at. %) films. Co-rich Co-Pt films, with thickness t ranging from 5 nm up to 2 μm, were prepared by electrodeposition on (0001)-oriented Ru underlayers. All samples displayed strong perpendicular magnetic anisotropy and high coercivity. Virgin magnetic domain structures for varying thickness were investigated by magnetic force microscopy (MFM). The observed increase of domain width with film thickness is well understood by full two-dimensional micromagnetic computations with no adjustable parameters. The easy-axis magnetization process, as observed by measuring virgin curves by magnetometry and imaging the corresponding magnetization configurations by MFM in variable field, consists of two stages separated by a well-defined critical field, marking the onset of domain wall propagation. A thorough analysis of the out-of-plane angular dependence of the switching field points out that unpinning of domain walls is the dominant magnetization process. [ABSTRACT FROM AUTHOR]