Freezing of anisotropic spin clusters in La1.98Sr0.02CuO4

TL;DR

This study reveals a spin-glass state in La$_{1.98}$Sr$_{0.02}$CuO$_4$ characterized by anisotropic, quasi-three-dimensional spin clusters that are frozen randomly, highlighting an intermediate magnetic phase related to stripe structures.

Contribution

It identifies and characterizes a new anisotropic spin-glass phase with quasi-3D spin clusters in La$_{1.98}$Sr$_{0.02}$CuO$_4$, bridging known magnetic phases in cuprates.

Findings

Longer magnetic correlation along the $a_{ortho}$ axis compared to $b_{ortho}$ axis.

Spin clusters exhibit anisotropic correlation lengths at 1.6 K.

The magnetic state is an intermediate phase between antiferromagnetic and incommensurate phases.

Abstract

A spin-glass compound, La$_{1.98}$Sr$_{0.02}$CuO$_4$, shows quasi-three-dimensional magnetic ordering below $\sim$40 K. A remarkable feature is that the magnetic correlation length along the orthorhombic $a\rm_{ortho}$ axis is much longer than that along the $b\rm_{ortho}$ axis, suggesting that the spin structure is closely related to the diagonal stripe structure. The spin-glass state can be expressed as a random freezing of quasi-three-dimensional spin clusters with anisotropic spin correlations ($\xi'_a\sim160$ \AA, $\xi'_b\sim25$ \AA, and $\xi'_c\sim4.7$ \AA at 1.6 K). The new magnetic state is important as an intermediate phase between the three-dimensional antiferromagnetic ordered phase in La$_2$CuO$_4$ and the incommensurate phase in La$_{1.95}$Sr$_{0.05}$CuO$_4$ in which the positions of the incommensurate peaks are rotated by 45$^\circ$ in reciprocal space about ($\pi$,$\pi$) from those observed in the superconducting La$_2$CuO$_4$ compounds.