Charge localization, magnetic order, structural behavior, and spin dynamics of(La−Tb)2/3Ca1/3MnO3manganese perovskites probed by neutron diffraction and muon spin relaxation

Abstract

Two microscopic techniques, muon spin relaxation and neutron diffraction, including small-angle neutron scattering (SANS), have been used to probe into the relevant mechanisms that determine the macroscopic behavior in the series $({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}{)}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}.$ The magnetic ground state at low temperatures evolves from ferromagnetic for $x<~0.25$ to spin glass for $0.33<~x<~0.75$ and finally antiferromagnetic for $x=1.$ Spin-glass regions were observed for $x>~0.25.$ We propose the existence of two different volume states associated with the metalliclike ferromagnetic state and the semiconductorlike paramagnetic, spin-glass, or antiferromagnetic states, respectively. SANS experiments reveal the existence of magnetic clusters for $x<~0.33.$ The magnetic correlation length diverges at ${T}_{c}$ for $x<~0.25$ while magnetic clusters of around 18 \AA{} stabilize in the $x=0.33$ compound at low temperatures. Muon spin relaxation experiments confirm the absence of microscopic local magnetic order for the $x=0.33$ compound and give evidence for the existence of static local fields randomly oriented below $\ensuremath{\approx}44\mathrm{K},$ bringing about a glassy magnetic state below that temperature. The remarkable electrical behavior in this series has been correlated with the microscopic properties.