Magnetic Dynamics and Spin Freezing in the Ferromagnetic Phase of Ba-Doped Perovskite Cobaltites

TL;DR

This study investigates the magnetic behavior of Ba-doped perovskite cobaltites, revealing phase separation, spin freezing, and strong magneto-elastic coupling influencing their magnetic dynamics.

Contribution

It provides new insights into the microscopic phase separation and spin freezing phenomena in Ba-doped cobaltites using muon spin relaxation and magnetization techniques.

Findings

Full volume inhomogeneous magnetic order below T_C

Microscopic phase separation into static and dynamic regions

Spin freezing occurs 35-55 K below T_C

Abstract

The magnetic properties of polycrystaline La0.5Ba0.5CoO2.5+d (d = 0.44 and 0.485) where investigated using muon spin relaxation and bulk magnetization experiments. Below a Curie temperature of T_C = 160 K and 180 K, respectively, a magnetic phase with a macroscopic ferromagnetic moment forms. muSR proves that the full volume inhomogeneously orders at T_C but that there is microscopically a phase separation into phase volumes possessing a fully static and a slow magnetic dynamic behavior. A peak in the dynamic relaxation rate 35 K respectively 55 K below the Curie temperature indicates the freezing of spin components. The spin fluctuations are thermally activated with a typical Jahn-Teller like phonon energy of E_a = 340 K. Together with co-operative Jahn-Teller distortions appearing below the spin freezing temperature, this points to a strong magneto elastic coupling as the cause for the magnetic fluctuations and the spin freezing.