Doped EuTe: A mixed magnetic system

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Abstract
The additional magnetic exchange introduced by doping of the magnetically ordering Eu chalcogenides has been investigated in the case of antiferromagnetic EuTe by means of the Faraday rotation, optical absorption, reflectivity measurements, luminescence, and photoconductivity. The magnetic contributions due to the electrons which were introduced by doping could always be well distinguished by comparison with measurements on undoped samples. Our results lead to the conclusion that at least in the nondegenerate EuTe the introduced electrons form large spin dressed particles, namely magnetic polarons or at low temperatures ferromagnetic spin clusters which can extend over as many as 2000 Eu ions. The size of these clusters and their degree of magnetic order is, however, dependent on temperature, applied magnetic field, and on the concentration of dopant. The existence of these spin clusters was verified by the observation of domain patterns with a polarizing microscope. Novel also is our discovery of a very large wavelength-independent Faraday rotation, which reaches values of up to 3600 deg/cm at 4.2 K. We have attributed this Faraday rotation to magnetic resonance of the spin clusters in the exchange fields of the magnetic sublattices.

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