Reversible and irreversible magnetization processes have been investigated in thin Ni sheets by m... more 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.
The imaginary part of the reversible susceptibility and its harmonics are measured on hard magnet... more The imaginary part of the reversible susceptibility and its harmonics are measured on hard magnetic materials by the modulation technique in a DC bias field. A singular point is observed in the second harmonic at the anisotropy field. An interpretation is given based on singular point detection approach
The force on electric and magnetic dipoles moving in vacuo is discussed in the general case of ti... more The force on electric and magnetic dipoles moving in vacuo is discussed in the general case of time-variable non-uniform fields and time-variable dipole moments, to first order in v/c and neglecting radiation reaction. Emphasis is given to the symmetry between electric and magnetic dipoles, justifying in general Ampère's equivalence principle, and showing that the difference between gilbertian and amperian dipoles (in vacuo) is only a question of interpretation. The expression for the force can be expressed in a variety of different forms, and each term of each form is susceptible of specific physical interpretations. Terms not described in the literature are pointed out. A possible experiment for verifying the (dual-Lorentz) force of an electric field on a magnetic current (and then " hidden momentum ") is proposed.
The interaction between point charge and magnetic dipole is usually considered
only for the ca... more The interaction between point charge and magnetic dipole is usually considered
only for the case of a rigid ferromagnetic dipole (constant-current): here the analysis of force,
momentum and energy (including the energy provided by the internal current generator) is
generalised to any magnetic dipole behaviour: rigid, paramagnetic, diamagnetic or
superconducting (perfectly diamagnetic).
A new type of high-sensitivity magnetic susceptometer is proposed. It utilises a long thin vibrat... more 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
Problems involving polarized plane waves and currents on sheets perpendicular to the wavevector i... more Problems involving polarized plane waves and currents on sheets perpendicular to the wavevector involve only one component of the fields, so it is possible to discuss electrodynamics in one dimension. Taking for simplicity linearly polarized sinusoidal waves, we can derive the field emitted by currents (analogous to dipole radiation in three dimensions) and reflection and transmission (analogous to Thomson scattering). Some aspects of the results are not intuitive, and for a physical understanding we need to see the problem in three dimensions. Eventually we apply these results to a linear model of the sheet, and we discuss the limit from a thick sheet.
Reversible and irreversible magnetization processes have been investigated in thin Ni sheets by m... more 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.
The imaginary part of the reversible susceptibility and its harmonics are measured on hard magnet... more The imaginary part of the reversible susceptibility and its harmonics are measured on hard magnetic materials by the modulation technique in a DC bias field. A singular point is observed in the second harmonic at the anisotropy field. An interpretation is given based on singular point detection approach
The force on electric and magnetic dipoles moving in vacuo is discussed in the general case of ti... more The force on electric and magnetic dipoles moving in vacuo is discussed in the general case of time-variable non-uniform fields and time-variable dipole moments, to first order in v/c and neglecting radiation reaction. Emphasis is given to the symmetry between electric and magnetic dipoles, justifying in general Ampère's equivalence principle, and showing that the difference between gilbertian and amperian dipoles (in vacuo) is only a question of interpretation. The expression for the force can be expressed in a variety of different forms, and each term of each form is susceptible of specific physical interpretations. Terms not described in the literature are pointed out. A possible experiment for verifying the (dual-Lorentz) force of an electric field on a magnetic current (and then " hidden momentum ") is proposed.
The interaction between point charge and magnetic dipole is usually considered
only for the ca... more The interaction between point charge and magnetic dipole is usually considered
only for the case of a rigid ferromagnetic dipole (constant-current): here the analysis of force,
momentum and energy (including the energy provided by the internal current generator) is
generalised to any magnetic dipole behaviour: rigid, paramagnetic, diamagnetic or
superconducting (perfectly diamagnetic).
A new type of high-sensitivity magnetic susceptometer is proposed. It utilises a long thin vibrat... more 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
Problems involving polarized plane waves and currents on sheets perpendicular to the wavevector i... more Problems involving polarized plane waves and currents on sheets perpendicular to the wavevector involve only one component of the fields, so it is possible to discuss electrodynamics in one dimension. Taking for simplicity linearly polarized sinusoidal waves, we can derive the field emitted by currents (analogous to dipole radiation in three dimensions) and reflection and transmission (analogous to Thomson scattering). Some aspects of the results are not intuitive, and for a physical understanding we need to see the problem in three dimensions. Eventually we apply these results to a linear model of the sheet, and we discuss the limit from a thick sheet.
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only for the case of a rigid ferromagnetic dipole (constant-current): here the analysis of force,
momentum and energy (including the energy provided by the internal current generator) is
generalised to any magnetic dipole behaviour: rigid, paramagnetic, diamagnetic or
superconducting (perfectly diamagnetic).
only for the case of a rigid ferromagnetic dipole (constant-current): here the analysis of force,
momentum and energy (including the energy provided by the internal current generator) is
generalised to any magnetic dipole behaviour: rigid, paramagnetic, diamagnetic or
superconducting (perfectly diamagnetic).