Photoinduced Magnetism and Conduction Electrons in Magnetic Semiconductors

Abstract

MnF, antiferromagnetic system by plane-polarized light through excitation of excitons in one of the two equivalent sublattices in the AFM was the subject of an outstanding experimental study [6]. A great amount of experimental work has been carried out2) with the aim of verifying and analyzing in detail the above-mentioned effects. Basic Principles of the Magnetic Semiconductor Theory Temperature dependence of the energy spectiqum of conduction electrons in ferromagnetic systemsThe theory of magnetic semiconductors is based on the s-f model (below the differences between localized d-and f-electrons are disregarded). With charge carriers having the same sign, the Hamiltonian for this model in the nearest-neighbour approximation has the following form:The first term in (2.1) describes the conduction electrons; g is the dimensionless coordinate of the atom, A the vector connecting the nearest neighbours, (T the spin projection. The second term describes the exchange interaction between conduction electrons and localized magnetic moments; here, Sg is the operator of the localized magnetic moment for the g atom, so,, are the Pauli matrices. The third term describes the "direct" (more precisely, the superexchange) interaction between localized magnetic moments which determines the type of magnetic ordering in the crystal. For certainly, the lattice of magnetic atoms is considered to be simple cubic.Magnetic semiconductors can be classified according t o the magnitude of the parameter ASIW, where S is the magnitude of the localized spin of the atom, W the conduction band width. Among semiconductors with a wide conduction band ( W > > A S ) are, e.g., EuO and EuS ferromagnets and EuTe and EuSe antiferromagnets.Among semiconductors with a narrow conduction band are, e.g., ferromagnetic spinels CdCr,Se, and others [74]. A theory of narrow-band magnetic semiconductors was described in detail earlier [63]. Below we shall analyze the results as applied to semiconductors with wide conduction bands. Qualitatively, in both cases the physical picture is the same, but if W > AX a more detailed analysis is possible [75, 2031.

Electromagnetic material changes for remote detection and monitoring: a feasibility study: Progress report

“…In magnetic materials, additional effects are expected based on the photomagnetic effect (e.g. [2][3][4], see Section 4). Similar effects of radiation on frequency change are anticipated for ferroelectrics which have domain or grain resonances in the 1-10 GHz range [5,6].…”

“…This should not be confused with the anticipated range of the overall radiation detection technique, which relies on the response generated in the material. The active volume was chosen as 0.1 cm 3 (1 x 1 x 0.1 cm thick) as a representative sample size that could be measured and compared with results.…”

“…Nagaev [3] explains the phenomena of the photomagnetic effect (PME) differently, referring to a quasiparticle called a ferron which consists of an electron and a ferromagnetic microregion. Rather than being simply a charge transfer of one electron between Fe 2+ and Fe…”

Photoinduced changes of magnetic anisotropy in substituted iron garnet

“…An optical exposure by linearly polarized radiation leads to change of a cubic magnetic anisotropy (CMA) in ferrite-garnets and causes an appearance of a complex (cubic and uniaxial photoinduced) magnetic anisotropy (CPMA) in these media [1]. Common conditions for this phenomenon are an existence of active (light sensitive and magnetically anisotropic) centers in inequivalent sites of the medium crystal lattice and a possibility of their photoinduced redistribution among these sites.…”

“…These ions can exist with different valence states in "a"-OIS of YIG [3]. Formation of photoinduced magnetic anisotropy (PMA) in YIG is based on changes in TM ions distribution among OIS caused by light-induced electron transition [1].Photoinduced microscopic kinetics of the centers and macroscopic dynamics (changes of an energy density e p and a symmetry axis orientation in space and time) of PMA were investigated for (1 1 0) plane of YIG crystal [4,5]. Strongly anisotropic ions Fe 2+ in "a"-OIS of YIG [4,5] and magneto-anisotropic doped centers [6] were considered as active centers.…”