Separation Between Antiferromagnetic and Ferromagnetic Transitions in Ru_1-xCu_xSr_2EuCu_2O_8+d

TL;DR

This study investigates magnetic phase transitions in Ru_1-xCu_xSr_2EuCu_2O_8+d, revealing phase separation and nanomagnetic clusters that explain conflicting magnetic and superconducting behaviors.

Contribution

It provides new insights into the separation of antiferromagnetic and ferromagnetic transitions and the presence of nanomagnetic clusters in Ru-based cuprates.

Findings

Separation of magnetic transitions increases with Cu doping.

Presence of nanomagnetic clusters above transition temperatures.

Phase separation explains conflicting magnetic-superconductivity data.

Abstract

The macroscopic magnetizations of Ru_1-xCu_xSr_2EuCu_2O_8+d with x between 0 and 0.15 were investigated. A ferromagnet-like transition as well as an antiferromagnet-like transition appear around T_M in the low-field magnetization and around T_AM in the high-field differential susceptibility, respectively. The separation between them, which is accompanied by a flat plateau in the magnetic C_p, increases with x. Superparamagnetic M(H) and slow spin dynamics, i.e. characteristics of nanomagnetic clusters, were observed far above T_M. A comparison with RuSr_2(Eu_1-yCe_y)Cu_2O_10+d and some manganites further suggests that a phase separation occurs, which can describe well the conflicting magnetic-superconductivity data previously reported.