Magnetism and Superconductivity in RuM1.5Ce0.5Sr2Cu2O10 (M=Eu and Y)

TL;DR

This study investigates the magnetic and superconducting properties of Ru-based cuprates, revealing complex magnetic ordering and decoupled superconducting and magnetic states, with coexistence of superconductivity and weak ferromagnetism in specific compositions.

Contribution

It provides new insights into the magnetic structures and coexistence of superconductivity and magnetism in RuM1.5Ce0.5Sr2Cu2O10 compounds, highlighting the effects of magnetic ordering and substitution.

Findings

Magnetic ordering occurs at TM=152 K with AFM structure.

Superconductivity appears below TC~38 K in specific compositions.

Magnetic and superconducting states are practically decoupled.

Abstract

RuY1.5Ce0.5Sr2Cu2O10, is not superconducting (SC) and orders magnetically at TM =152 K. The Ru moment at 5K is 0.75 mB. Ferromagnetic hysteresis loops are observed below Tirr= 100 K. At 100 K, the remanent magnetization (Mrem) and the coercive field (HC) become zero. Surprisingly, at Tirr <T< TM a reappearance of antiferromagnetic (AFM) hysteresis loops are observed with a peak at 120 K for both Mrem and HC. The paramagnetic constants are: Peff =2.06 mB (greater than the 1.73 mB expected for low spin Ru5+) and q= 136 K which agrees well with TM. Substitution of Zn (2.5% atm.) for Cu in RuEu1.5Ce0.5Sr2Cu2O10 (TC=38 K), suppresses TC but does not affect the magnetic features such as: TM and Tirr, Mrem and HC. This indicates that both SC and magnetic states are practically decoupled. We argue that the magnetic structure of this system becomes (i) AFM ordered at TM. (ii) Due to the tilting of the RuO6 octahedra away from the crystallographic c axis, at Tirr < TM, weak-ferromagnetic (W-FM) order is induced by the canting of the Ru moments. (iii) At TC (TM/TC~4), the specific materials (M=Eu, Gd) become SC. Below TC, both SC and W-FM states coexist.