Charge localization, magnetic order, structural behavior, and spin dynamics of (La-Tb)(2/3)Ca1/3MnO3 manganese perovskites probed by neutron diffraction and muon spin relaxation

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 (La1-xTbx)(2/3)Ca1/3MnO3. The magnetic ground state at low temperatures evolves from ferromagnetic for x less than or equal to 0.25 to spin glass for 0.33 less than or equal to x less than or equal to 0.75 and finally;antiferromagnetic for x=1. Spin-glass regions were observed for x greater than or equal to 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 less than or equal to 0.33. The magnetic correlation length diverges at T-c for x less than or equal to 0.25 while magnetic clusters of around 18 Angstrom 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 approximate to 44 K, bringing about a glassy magnetic state below that temperature. The remarkable electrical behavior in this series has been correlated with the microscopic properties.