SQUID Magnetometry and Magneto-Optics of Epitaxial EuSe

K. Rumpf a , P. Granitzer a , W. Kellner b , R. Kirchschlager c , S. Janecek c , H. Pascher b and H. Krenn a a Institut für Experimentalphysik, Universität Graz, 8010 Graz, Austria b Experimentalphysik I, Universität Bayreuth, 95440 Bayreuth, Germany c Institut für Halbleiter- u. Festkörperphysik, Universität Linz 4040 Graz, Austria

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The complicated (H,T)-magnetic phase diagram of EuSe is caused by the critical balance between nearest and next nearest neighbour exchange interaction (J NN =0.119K and J NNN =-0.1209K) and leads to various spin arrangements NNSS..., NSN..., NNS, NNN... [NS denotes opposite ferromagnetic order in adjacent (111) planes]. Beside the subtle local exchange of 5d-t 2g electrons and localized holes with neighbouring Eu-4f spins, obviously also the strain status influences the occurrence of these different phases. We investigate the magnetic ordering phenomenon in a strained 2.5μm EuSe film on BaF 2 substrate by SQUID magnetometry and magneto-optics like spectral Faraday- and Kerr-effect measurements for temperatures from 2K up to 200K and for magnetic fields up to 5T. The magneto-optical probe monitors the local environment of the photoexcited electron--hole pair, called magnetic exciton, located within a ferromagnetic surrounding (photoinduced magnetic polaron), whereas the integral magnetization measured by SQUID is most sensitive to long-range magnetic ordering. In spite of the dissimilarity of measurement techniques we find an influence of the long-range magnetic order (e.g. of the NNS- or NNN-matrix) on the non-resonant Kerr reflection. The complementarity of SQUID and magneto-optical methods is stringent only in the (resonant) spectral regime, where magnetic polarons are formed.

DOI: 10.12693/APhysPolA.105.621 PACS numbers: 75.50.Pp, 78.20.Ls, 07.55.Jg