EMR studies of the internal motion of Mn(4+) ions in the Sr overdoped (La(1-x)Sr(x))(Ga(1-y)Mn(y))O3 (x/y up to 8) supplemented by magnetic and optical spectroscopy measurements.
The effect of the Sr doping on electronic structure in single crystals of (La(1-x)Sr(x))(Ga(1-y)Mn(y))O3 solid solutions (LSGM) is investigated by means of electron magnetic resonance (EMR). The EMR results are supplemented by magnetic susceptibility and optical spectroscopy measurements. The compositions with small concentration of Mn doping (y<1%) and overdoped content of Sr (the ratio x(Sr)/y(Mn) up to 8) are used to maximally enhance the role of divalent doping. The experimental results provide evidence of the holes delocalization in the overdoped compound (x(Sr)/y(Mn)>1). This delocalization is accompanied by appearance of the new charge transfer transitions in the optical spectrum and dynamical valence change of manganese atoms. Additionally we observe the thermally activated narrowing of resonance EMR lines due to the internal motion, which is characterized by the energy barrier depending strongly on the ratio x(Sr)/y(Mn). The energy barrier is found to be associated with the charge carrier (hole) self-trapped energy. Fitting the EMR spectra in three orthogonal planes to an orthorhombic spin Hamiltonian enables extracting the zero-field splitting (ZFS) parameters and the Zeeman g-factors for Mn(4+) (S=3/2) ions in LSGM. The experimental ZFS parameters are modeled using superposition model analysis based on an orthorhombic symmetry approximation.
Institute of Physics, Polish Academy of Science, 02-668 Warsaw, Al. Lotników 32/46, Poland. Electronic address: pavloa@ifpan.edu.pl.
Pavlo
P
Aleshkevych
Institute of Physics, Polish Academy of Science, 02-668 Warsaw, Al. Lotników 32/46, Poland.
Jan
J
Fink-Finowicki
Institute of Physics, Polish Academy of Science, 02-668 Warsaw, Al. Lotników 32/46, Poland.
Tatiana
T
Zayarnyuk
Institute of Physics, Polish Academy of Science, 02-668 Warsaw, Al. Lotników 32/46, Poland.
Igor
I
Radelytskyi
Institute of Physics, Polish Academy of Science, 02-668 Warsaw, Al. Lotników 32/46, Poland.
Marek
M
Berkowski
Institute of Physics, West Pomeranian University of Technology, Al. Piastów 17, 70-310 Szczecin, Poland.
Czeslaw
C
Rudowicz
Institute of Physics, West Pomeranian University of Technology, Al. Piastów 17, 70-310 Szczecin, Poland.
Pawel
P
Gnutek
EMR; Hole delocalization; Internal motion; Superposition model