Magnetisation processes

Fig. 62. Configuration of magnetisation and magnetic moment in the sandwich TbCo/NdCo/TbCo film in zero magnetic field (a) and during the (de)magnetisation processes (b-e).

Nanoparticle systems can be prepared by various deposition techniques (sputtering, cluster deposition) and in particular, serve as model systems to study magnetisation processes at the nanoscale. In addition, the magnetic... 

The presence of a reversed polarity component can be demonstrated in one Bone Chamber sample, and there is evidence for reversed polarity components in several of the samples from Reed Chamber. At some stage between deposition of the Buchan cave sediments and the present, they have been exposed to a reversed field. Although brief intervals of intermediate and reversed polarity are known from the Brunhes Chron (e.g., the Blake and Emperor events), these total only about 5% of its 780,000 year extent (Jacobs, 1984 Cande and Kent, 1995). Consequently, it is most likely that the cave sediments have been in place since at least 780 ka. Understanding how the age of acquisition of the reversed polarity component relates to the age of cave sedimentation depends on an appreciation of the magnetisation process involved. 

Magnetisation processes are affected by stress. These phenomena, which can be considered as the opposite of magnetostriction, can also be visualised on the basis of spin-orbit coupling. The application of a stress affects the ability of orbitals to rotate under the influence of a magnetic field. Stress effects can be expressed in terms of a stress anisotropy,... 

Fig. 4.56. Irreversible magnetisation process. After application and removal of a strong field, the sample is in the remanence, however, due to the demagnetising field. Hi. induction decreases to the Ba value. Operation point is P.

For amorphous alloys described by the random anisotropy model (Cochrane et al. 1978) as well as for polycrystalline materials, the EMD is isotropically distributed. In this case, spin orientation and domain walls are randomly distributed. The magnetisation process therefore consists of two steps (i) the motion of 180°-domain walls leading to a magnetisation of MJ2 without any magnetostriction, and (ii) the rotation of spins into... 

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