Charge localization, magnetic order, structural behavior, and spin dynamics of(La−Tb)2/3Ca1/3MnO3manganese 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 $({\mathrm{La}}_{1-x}{\mathrm{Tb}}_x{)}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3.$ 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 $x=1.\mathrm{}$ Spin-glass regions were observed for $x>~\mathrm{0.25.}$ 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 $x<~\mathrm{0.33.}$ The magnetic correlation length diverges at $T_c$ for $x<~0.25$ while magnetic clusters of around 18 Å stabilize in the $x=0.33\mathrm{}$ compound at low temperatures. Muon spin relaxation experiments confirm the absence of microscopic local magnetic order for the $x=0.33\mathrm{}$ compound and give evidence for the existence of static local fields randomly oriented below $\approx 44\mathrm{K},$ bringing about a glassy magnetic state below that temperature. The remarkable electrical behavior in this series has been correlated with the microscopic properties.