Significant suppression of weak ferromagnetism in (La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$

TL;DR

This study investigates the magnetic properties of (La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$, revealing a significant suppression of weak ferromagnetism below a structural transition, and compares findings with theoretical models to infer the crystal symmetry.

Contribution

The paper provides experimental evidence of weak ferromagnetism suppression in (La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$ and links it to changes in crystallographic symmetry, enhancing understanding of magnetic behavior in doped cuprates.

Findings

Weak ferromagnetic moment suppressed by approximately 70% below $T_s$

Magnetic behavior similar to La${}_2$CuO${}_4$ in the orthorhombic phase

(La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$ is in the low-temperature less-orthorhombic phase below $T_s$

Abstract

The magnetic structure of (La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$ has been studied by magnetization measurements of single crystals, which show antiferromagnetic long-range order below $T_N$ = 265 K and a structural phase transition at $T_s$ = 130 K. At $T_s < T < T_N$, the Cu spin susceptibility exhibits almost the same behavior as that of La${}_2$CuO${}_4$ in the low-temperature orthorhombic phase, which indicates the existence of finite spin canting out of the CuO${}_2$ plane. At $T < T_s$, the magnitude of the weak-ferromagnetic moment induced by the spin canting is suppressed approximately by 70{%}. This significant suppression of the weak-ferromagnetic moment is carefully compared with the theoretical analysis of weak ferromagnetism by Stein {\it et al.} (Phys. Rev. B {\bf 53}, 775 (1996)), in which the magnitude of weak-ferromagnetic moments strongly depend on the crystallographic symmetry. Based on such comparison, below $T_s$ (La${}_{1.8}$Eu${}_{0.2}$)CuO${}_4$ is in the low-temperature less-orthorhombic phase with a space group of $Pccn$. We also discuss the possible magnetic structure of the pure low-temperature tetragonal phase with space group $P4_2/{ncm}$, which is relevant for rare-earth and alkaline-earth ions co-doped La${}_2$CuO${}_4$.