It looks like you're new here. If you want to get involved, click one of these buttons!
•Diamagnetism is similar to electrostatic polarization of a dielectric in that the induced magnetic moment tends to oppose the field that creates it.•Paramagnetism is created when atoms with permanent dipole moments tend to align with an external magnetic field; the resulting field is greater that of the external magnetic field•Ferromagnetism is similar to paramagnetism except much stronger and occurs primarily in iron, nickel, cobalt Diamagnetism •Diamagnetic materials do not have permanent dipole moments•Diamagnetism is the weakest of the three types of magnetism in materials•All materials exhibit diamagnetism but it is overwhelmed in paramagnetic and ferromagnetic materials•Diamagnetism arises because the dipole moments induced in atoms tend to line up opposite of the direction of the external magnetic field that created them•Diamagnetic materials thus weaken the external field
Electric and magnetic fields: different aspects of the same phenomenonMain article: Relativistic electromagnetismAccording to the special theory of relativity, the partition of the electromagnetic force into separate electric and magnetic components is not fundamental, but varies with the observational frame of reference: An electric force perceived by one observer may be perceived by another (in a different frame of reference) as a magnetic force, or a mixture of electric and magnetic forces.Formally, special relativity combines the electric and magnetic fields into a rank-2 tensor, called the electromagnetic tensor. Changing reference frames mixes these components. This is analogous to the way that special relativity mixes space and time into spacetime, and mass, momentum and energy into four-momentum.
The geometrical properties of ultra-low-frequency (ULF) waves in the magnetosphere originate primarily from constraints imposed by the ambient medium. Since long-period ULF waves span global dimensions, the normal modes are constrained in spatial extent by structures that define the magnetosphere---the magnetopause, magnetotail, plasmapause and ionosphere. ULF wave characteristics also vary continuously throughout the magnetosphere because the geomagnetic field and magnetospheric plasma are strongly inhomogeneous on the length scales of long-period waves. Inhomogeneity limits the accessibility of some ULF waves in particular regions of the magnetosphere. These constraints enter all realistic descriptions of ULF wave propagation, and, together with a physical model for propagation, they suggest some optimal choices for geometrical representation of the wave fields.The physics of magnetospheric ULF waves, including dynamics, mode coupling and interactions with various boundaries, are described under a wide variety of conditions by the equations of one-fluid magnetohydrodynamics (MHD) [cf. Southwood and Hughes, 1983; Samson, 1991]. An important property of the MHD theory, that bodes for the choice of geometry, is its prediction of strongly anisotropic behavior. MHD electric fields are locally orthogonal to the magnetic field in the one-fluid theory, and the propagation of two of the three basic MHD modes---the slow magnetosonic wave and the shear wave---exhibit magnetic guidance, whereas the fast magnetosonic wave alone exhibits a more isotropic propagation. The fact that the magnetic lines of force place strong dynamical constraints on MHD characteristics is a compelling incentive to analyze magnetospheric ULF wave properties in a geometry defined by the geomagnetic field, comprised of the internal field of the earth and persistent external deformations attributed to large-scale magnetospheric current systems [ Stern, 1994].
Most of the electrostatic demonstrations that follow use an electrophorus for the supply of charge. Volta is generally credited with inventing the electrophorus perpetuum in 1775. Our modern version uses a sheet of Teflon for the dielectric plate which is charged by rubbing it with rabbit's fur. It was called perpetuum because the charge does not get used up (when charging by induction). A metal disk with an insulating handle is held over and close to the dielectric plate. The dielectric (negative in charge) repels the electrons from the lower surface of the disk to the top surface. These electrons are then allowed to escape by momentarily grounding the disk (by touching it with a finger). The disk with the remaining positive charge is then lifted away from the dielectric and this charge is used for the desired purpose. Any number of charges can be obtained from the electrophorous in this manner without depleting its charge. This is because work is done by the hand that lifts the disk against the attractive electrostatic force. The electrophorus will keep its charge for many months. Of course, if the metal disk is allowed to touch the dielectric, it will become charged by conduction (negatively) and this does deplete the charge of the electrophorus.
As technology moves toward 5~7 nanometer spaced head-disk systems for high density magnetic recording, the mechanical interaction between head-slider and disk-media will strongly affect the magnetic integrity of magnetic head-disk systems. It is time to pay more attention to the study of the relationship among magnetic data on disk media, readback signal from magnetic head, and mechanical interaction between head-slider and disk-media. Therefore, the concept of tribo-magnetics is proposed in this work to study the relationship between mechanical interaction in head-disk interface and the magnetic performance of the magnetic head-disk systems. The work reported in this paper covers 3 major parts of tribomagentics: tribo-decay, tribe-noise and tribomagnetic testing. Results indicate that head-disk interaction can disturb the stability of the recorded magnetic transitions and lead to a decay of readback signal-tribo-decay. Furthermore, the MR/GMR heads are sensitive to the energy transferring between head and disk when the head interacts mechanically with disk media. As a result, tribo-noise will be generated and the reading capability of the head will be affected. Head-disk spacing is one of the most important head-disk interface parameters. The relationship between head-disk spacing and the read/write performance of the head-disk system can he used to characterize the dynamic variation of head-disk interface. Two new methods are reported in this work to increase the testing sensitivity and the testing range of in-situ measurement of the head-disk spacing, including a triple harmonic method for high sensitivity in-situ measurement and a scanning carrier current method for load/unload applications which requires larger testing range