Orbital domain state and finite size scaling in ferromagnetic insulating manganites

TL;DR

This study uses NMR and neutron scattering to reveal a phase transition at 70 K in ferromagnetic manganites, characterized by orbital domain formation and inhomogeneous orbitally ordered states influenced by doping.

Contribution

It provides new evidence of orbital domain states and finite size scaling effects in ferromagnetic manganites, linking local magnetic and orbital phenomena to macroscopic phase transitions.

Findings

Localization of Mn(3+,4+) states below 70 K

Divergence of spin-lattice relaxation rates at T(tr)

Finite size scaling of transition temperature with doping

Abstract

55Mn and 139La NMR measurements on a high quality single crystal of ferromagnetic (FM) La0.80Ca20MnO3 demonstrate the formation of localized Mn(3+,4+) states below 70 K, accompanied with strong anomalous increase of certain FM neutron Bragg peaks. (55,139)(1/T1) spin-lattice relaxation rates diverge on approaching this temperature from below, signalling a genuine phase transition at T(tr) approx. 70 K. The increased local magnetic anisotropy of the low temperature phase, the cooling-rate dependence of the Bragg peaks, and the observed finite size scaling of T(tr) with Ca (hole) doping, are suggestive of freezing into an orbital domain state, precursor to a phase transition into an inhomogeneous orbitally ordered state embodying hole-rich walls.