Formation of magnetic glass in calcium doped YBaCo2O5.5 cobaltites

TL;DR

This study reports the discovery of magnetic glass-like behavior in calcium-doped YBaCo2O5.5 cobaltites, showing kinetic arrest and phase coexistence at low temperatures, which can be manipulated by magnetic field and temperature.

Contribution

First demonstration of magnetic glass formation in calcium-doped YBaCo2O5.5 cobaltites, revealing phase separation and tunable low-temperature magnetic states.

Findings

Magnetic glass-like behavior observed in calcium-doped cobaltites.

External magnetic field influences phase coexistence and glass formation.

Low temperature state involves phase separation with ferromagnetic and antiferromagnetic clusters.

Abstract

The d.c. magnetization and magnetic relaxation studies of the calcium doped samples, Y0.95Ca0.05BaCo2O5.5 and YBa0.95Ca0.05Co2O5.5, show the existence of a magnetic glass like behaviour in the family of cobaltites for the first time. Our investigations reveal glass-like arrest of kinetics at low temperature which prevents the system from reaching its magnetic ground state. We show that the low temperature state of these calcium doped phases, which consists of coexisting antiferromagnetic and ferro (or ferri) magnetic phase fractions, can be tuned in a number of ways. Our observations establish that the low temperature state of this oxide is not in thermal equilibrium. The glassy state is formed with the assistance of an external magnetic field, which makes it distinctly different from the more well known metastable state, the spin glass state. The cooling field can tune the fractions of the coexisting phases, and the glass-like state formed at low temperature can also be devitrified by warming the sample. The role of Ca doping in the appearance of these phenomena is discussed in terms of phase separation, involving Co3+ disproportionation into Co4+ ferromagnetic clusters and Co2+ antiferromagnetic clusters.