Orbital domain state and finite size scaling in ferromagnetic insulating manganites.
55Mn and 139La NMR measurements on a high quality single crystal of ferromagnetic (FM) La0.80Ca0.20MnO3 demonstrate the formation of localized Mn(3+,4+) states below 70 K, accompanied by a strong cooling-rate dependent increase of certain FM neutron Bragg peaks. (55,139)(1/T(1)) spin-lattice and (139)(1/T(2)) spin-spin relaxation rates are strongly enhanced on approaching this temperature from below, signaling a genuine phase transition at T(tr) approximately 70 K. The disappearance of the FM metallic signal by applying a weak external magnetic field, the different NMR radio-frequency enhancement of the FM metallic and insulating states, and the observed finite size scaling of T(tr) with Ca (hole) doping, as observed in powder La(1-x)CaxMnO3 samples, are suggestive of freezing into an inhomogeneous FM insulating and orbitally ordered state embodying "metallic" hole-rich walls.
Papavassiliou
G
G
Institute of Materials Science, NCSR, Demokritos, 153 10 Aghia Paraskevi, Athens, Greece.
Pissas
M
M
Belesi
M
M
Fardis
M
M
Dolinsek
J
J
Dimitropoulos
C
C
Ansermet
J P
JP