Direct observation of the magnetic polaron

Abstract

Semiconductor electronics has so far been based on the transport of charge carriers while storage of information has mainly relied upon the collective interactions of spins. A new discipline known as spintronics proposes to exploit the strong mutual influence of magnetic and electrical properties in magnetic semiconductors, which promise new types of devices and computer technologies. The mechanism for such phenomena involves the concept of magnetic polarons-microscopic clouds of magnetization composed of charge carriers and neighboring magnetic ions-which determine most of the electrical, magnetic, and optical properties of the material. In spite of the importance of this quasiparticle, its observation remains a formidable challenge. Here we report that, using the positive muon as both a donor center and a local magnetic probe, we have been able to generate and detect the magnetic polaron and determine its size and magnetic moment in the magnetic semiconductor EuS.

Spin correlations and colossal magnetoresistance inHgCr2Se4

“…16,18,19,39 The magnetic polaron is a nanoscale charge-spin composite, in which a charge carrier polarizes a number of localized spins in the lattice of magnetic ions via the exchange interaction. The existence of magnetic polarons have been confirmed by a lot of experiments, including muon spin resonance, 40,41 and Raman scattering. 42,43 Thermally activated transport has been observed in many The resistivity follows ρ xx ∼ exp(∆ b /k B T ), mostly in a temperature range of a few times T C to room temperature, where ∆ b is attributed to the binding energy of individual magnetic polarons, typically of order 0.1 eV.…”

“…18 The sd exchange interaction (or s-f interaction in rare earth compounds) provides strong polarizing force for a small number of lattice spins overlapping with the donor wavefunctions. 9,10,19,40,41 At high temperatures, spin correlation length ξ is too short to be relevant. The lattice spins in the polarons can thus be modeled as a uniformly polarized core of sub-nm size, separated by a sharp boundary from the paramagnetic background with randomized spins.…”

Direct Epitaxial Integration of the Ferromagnetic Semiconductor EuO with Silicon for Spintronic Applications

“…Concentrated MS offer several important advantages over DMS such as higher magnetisation, spatial magnetic homogeneity and wider range of conductivity tuning by doping, so that they can be used as spin filters in the insulating state and as spin injectors when doped [22,23]. Being doped, though, at high temperature, these materials typically enter into dominant states that are not spatially homogeneous due to formation of magnetic polarons -few-body systems comprised of electron and local magnetic moments of the host [20,[24][25][26][27]. However, this unwanted formation does not take place when magnetisation of the lattice is significant, leaving the host material perfectly homogeneous in the region of its employment as a spin injector [25][26][27].…”

“…Being doped, though, at high temperature, these materials typically enter into dominant states that are not spatially homogeneous due to formation of magnetic polarons -few-body systems comprised of electron and local magnetic moments of the host [20,[24][25][26][27]. However, this unwanted formation does not take place when magnetisation of the lattice is significant, leaving the host material perfectly homogeneous in the region of its employment as a spin injector [25][26][27].Owing its outstanding magnetic and transport properties among other MS, EuO has recently attracted much attention as having tremendous potential for semiconductor spintronics, in particular, when integrated with Si [18,[28][29][30]. Not only does doped EuO exhibit a spin polarization close to 100% due to enormous (~0.6 eV) spin splitting of its conduction band but also it can be conductance-matched with Si by doping with oxygen vacancies or trivalent rare-earth atoms such as Gd, La or Lu [18,[30][31][32][33].…”

State Energies and Transition Frequency of Strong-Coupling Polaron in an Anisotropic Quantum Dot

“…Because of the wide device applications and many new effects in such structures, understanding their electronic and transport properties is of particular importance. Consequently, there has been a large amount of experimental work [1][2][3] on QD. Meanwhile, many investigators studied its properties in many aspects by a variety of theoretical methods [4][5][6][7][8].…”