Basic Concepts of Electron Paramagnetic Resonance
The electron paramagnetic resonance is observable in substances that contain electronic magnetic dipoles.
- PDF / 2,456,018 Bytes
- 111 Pages / 439.37 x 666.142 pts Page_size
- 81 Downloads / 244 Views
Basic Concepts of Electron Paramagnetic Resonance
1.1
Magnetic Dipole
The electron paramagnetic resonance is observable in substances that contain electronic magnetic dipoles. We list examples of systems in which there are unpaired electrons: 1. Transition and rare-earth elements, which have unfilled d and f shells, as well as the atoms and ions of elements in the periodic table, having unpaired s and p electrons. 2. Localized donor and acceptor states in semiconductor materials, nanostructures. 3. Conduction electron and holes in solids. 4. Point defects produced in a material by electromagnetic or particle irradiation, color centers. 5. Stable free radicals. 6. The excited state of defects that are not paramagnetic in the ground state, excitations (excitons, electron-hole pairs). 7. Systems for solar power engineering (photovoltaic). 8. Biological objects in which free radicals are involved in the metabolism, red ox processes occurring in single-electron states. 9. Products of the photosynthesis in which a primary oxidant and a reductant are formed in the initial primary photochemical act. 10. Metal proteins containing transition elements Fe, Mn, Cu, Ni, Co, etc. 11. Spin labels in biology. 12. Molecular oxygen having the paramagnetic ground state. etc.
© Springer-Verlag GmbH Austria 2017 P.G. Baranov et al., Magnetic Resonance of Semiconductors and Their Nanostructures, Springer Series in Materials Science 253, DOI 10.1007/978-3-7091-1157-4_1
1
2
1.1.1
1 Basic Concepts of Electron Paramagnetic Resonance
Magnetic Dipole Moment
The elementary source of the magnetic field is the magnetic dipole, in contrast to the elementary source of the electric field, which can be created by positive or negative point charges. The magnetic monopole, a magnetic analogue of an electric charge, has never been observed. The magnetic dipole can be represented as a planar closed loop that carries an electric current I (Fig. 1.1a). Its magnetic dipole moment, vector ~ l, is defined as a vector that points out of the plane of the current loop and has a magnitude equal to the product of the current and the loop area: 1 ~ n ðCGS system of unitsÞ: l ¼ IS~ n ðSI system of unitsÞ~ l ¼ IS~ c
ð1:1Þ
Here, I is the current in the loop, S is the loop area, and ~ n is the normal to the loop in accordance with right-hand grip rule in relation to the current direction. In SI units for the current-loop definition, the magnetic moment is measured in ampere–square meters (A m2). In the equation for torque on a moment in the magnetic field, the moment is measured in joules per tesla (J T−1), and these two representations are equivalent.
1.1.2
Magnetic Field Produced by a Magnetic Dipole Moment
A magnetic dipole produces a dipolar magnetic field ~ B in the space surrounding the system (Fig. 1.1b), similarly to an electric dipole, which is the source of an electric field (using the dipole field as an approximation for points far from the loop),
Fig. 1.1 a Magnetic moment ~ l of a planar current having magnitude I and enclosing an area S. b Externa
Data Loading...
