Magnetic Polarons in EuO

Abstract

The existence of spin-polarized complexes or magnetic polarons in magnetic semiconductors has been suggested theoretically some time ago, but up to now there is little experimental evidence of this phenomenon. With this in view, electron paramagnetic resonance is investigated (g-factor and linewidth temperature coefficient) and also several other electrical and magnetic parameters of EuO-based magnetic semiconductors with various donor concentrations (oxygen vacancies or Gd3+ ions substituting Eu2+ ions). The results of the investigation show that in a limited region of donor concentrations and temperatures there occurs a localization of charge carriers which may be attributed to the formation of magnetic polarons. Die Existenz von spinpolarisierten Komplexen oder magnetischen Polaronen in magnetischenHalbleitern wurde theoretisch vor einiger Zeit vorhergesagt, doch bis heute gibt es wenige experimentelle Hinweise fur dieses Phiinomen. In dieser Hinsicht werden die elektronenparamagnetische Resonanz (g-Faktor und Temperaturkoeffizient der Linienbreite) und auch einige andere elektrische und magnetische Parameter von magnetischen Halbleitern auf EuO-Basis mit verschiedenen Donatorkonzentrationen (Sauerstoff-Leerstellen oder Gda+-Ionen die Euzf-Ionen substituieren) untersucht. Die Ergebnisse zeigen, daD in einem begrenzten Bereich von Donatorkonzentrationen und Temperaturen eine Lokalisierung der Ladungstriiger auftritt, die der Bildung von magnetischen Polaronen zugeschrieben werden kann.

Magnetic properties of pure and Gd-doped EuO probed by NMR

“…Using a similar derivation than the one leading to (14) in the paper of Barak et al, 43 we obtained: …”

“…11,12,13,14,15 CMR has also been observed in manganites. Nuclear magnetic resonance (NMR) has been proven to be a good technique to study local magnetic microstructures such as stripes and magnetic polarons.…”

Epitaxy, stoichiometry, and magnetic properties of Gd-doped EuO films on YSZ (001)

“…7,8,9,10,12,13,14,15,18 It was inferred that stoichiometry problems could add to an extra increase in T C . 5,11 In this respect it is interesting to note that indeed oxygen deficiencies in Gd-free EuO samples already lead to enhancements of T C up to 140-150 K. 17,19,20 In our case we can exclude the presence of oxygen vacancies: the samples all were grown under Eu-distillation conditions, and under these conditions we have observed for the pure EuO films that they have the bulk T C value of 69 K and that they remain semiconducting and are, in fact, extremely insulating down to the lowest temperatures. 21 Our experimental finding of a smooth enhancement of T C as a function of Gd concentration is in qualitative agreement with recent mean-field theoretical models.…”

Temperature dependent phase transition of EuO on MgO(100)

“…14 Interestingly, it also shows a colossal magnetoresistance ͑CMR͒ behavior in that an applied field shifts the metal-insulator transition ͑MIT͒ temperature, as has been reported for La 1−x Sr x MnO 3 . [15][16][17] However, EuO films are difficult to fabricate because they form only under particular growth conditions ͑e.g., oxygen partial pressure and substrate temperature͒, and they are easily changed into Eu 2 O 3 films if the growth conditions are not rigorously maintained. 18,19 In the present study, we investigate the change in polarization ͓P=͑I spin up − I spin down ͒ / ͑I spin up + I spin down ͔͒ and magnetic and electronic characteristics of a EuO film on a MgO͑100͒ surface as a function of temperature using spin resolved photoemission spectroscopy ͑SRPES͒, x-ray absorption spectroscopy ͑XAS͒, and low energy electron diffraction ͑LEED͒.…”