Magnetic Polarization Work

As might be anticipated from the Maxwellian symmetry of electric and magnetic phenomena, a completely parallel magnetic work form dwmag arises from magnetic polarization in 

H is the magnetic field strength, and M. is the magnetization (total magnetic moment) of the substance. In words  

Magnetic work The transfer of a quantity of magnetization (extensive) through a difference in magnetic field strength (intensive). 

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In Sect. 2.3 we saw that if the substrate is magnetic the SEs may be longitudinally spin polarized. Work by Naaman and coworkers has shown that spin-polarized electrons produced by circularly polarized laser light illumination of an... 

In this chapter we will present, mainly for the photochemist, an overview of the development of photochemically induced magnetic polarization by providing a brief summary of the background theory (Section II) and the various experimental techniques (Secion III). No attempts will be made to cover in detail all aspects of the enormous amount of work that has been published in this field. Instead, we shall aim at general illustrations of the utility and application of CIDEP/CIDNP to photochemistry. We shall draw heavily from our own experience in this field, which is most extensive in electron polarization studies. 

In this section no attempt is made to present a comprehensive review of all the work that has been done in the magnetic polarization field. Instead, we shall emphasize those examples which illustrate the principle of CIDEP and CIDNP in photochemistry and which may be of special interest to the practicing photochemist. Interesting relationships between CIDEP and CIDNP... 

Fig. 35. Comparision of the hard magnetic properties of two hard magnetic materials a and b. (Left) Flux density B (full lines) and magnetic polarization J (dashed lines) as a function of the demagnetizing field strength H. (Right) Product BH (horizontal axis) plotted versus B (vertical axis) for both materials a and b. The working point corresponding to (BFf)max is indicated on the B(H) curve (left point for material a and b) by a filled and open circle, respectively.

A more complex magnetic behaviour is expected for RI compounds in which the second component is a 3d transition metal such as Mn, Fe, or Co. The magnetic behaviour of the transition metal component is now based on the magnetic polarization of the electronic d-bands. Consequently, in this section we summarize the theory of itinerant or band magnetism and its application to transport properties. We begin with the Stoner-Wohlfarth model and include a summary of recent works. 

Here —PdV refers to the sign convention recommending that work done on the system is positive as the compression work leads to —dV and positive work. Some other types of work interactions are surface deformation adA, where a is the surface tension and dA is the change in surface area), electric polarization, magnetic polarization, frictional, and stress-strain. 

If we consider an isotropic region with no electrical or magnetic polarization, the only work variable is the... 

Called CYCLCROP (cyclic cross polarization) [24], the method works by first exciting all magnetization. Cross polarization pulses are then applied at the specific Lannor frequencies of the H- C pair of interest so as to transfer coherence from to C. The transfer pulses must satisfy the Hartmaim-Halm condition... 

Concluding this section, two interesting variants of the STM should be addressed. The spin-polarized STM (SPSTM), which works with a ferromagnetic tip, can be used to probe surface magnetism with high resolution [5.47, 5.48]. Other modifications of the STM involve electromagnetic radiation, whereby two basic concepts can... 

Much of the Pt Mossbauer work performed so far has been devoted to studies of platinum metal and alloys in regard to nuclear properties (magnetic moments and lifetimes) of the excited Mossbauer states of Pt, lattice dynamics, electron density, and internal magnetic field at the nuclei of Pt atoms placed in various magnetic hosts. The observed changes in the latter two quantities, li/ (o)P and within a series of platinum alloys are particularly informative about the conduction electron delocalization and polarization. 

Other optical and spectroscopic techniques are also important, particularly with regard to segmental orientation. Some examples are fluorescence polarization, deuterium nuclear magnetic resonance (NMR), and polarized IR spectroscopy [4,246,251]. Also relevant here is some work indicating that microwave techniques can be used to image elastomeric materials, for example, with regard to internal damage [252,253]. 

Various types of work in addition to pV work are frequently involved in experimental studies. Research on chemical equilibria for example may involve surfaces or phases at different electric or magnetic potentials [11], We will here look briefly at field-induced transitions, a topic of considerable interest in materials science. Examples are stress-induced formation of piezoelectric phases, electric polarization-induced formation of dielectrica and field-induced order-disorder transitions, such as for environmentally friendly magnetic refrigeration. 

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