Single-crystal growth and dependences on the hole concentration and magnetic field of the magnetic ground state in the edge-sharing CuO$_2$ chain system Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$

TL;DR

This study investigates how hole concentration and magnetic field influence the magnetic ground states in Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$ single crystals, revealing transitions from antiferromagnetic order to spin-glass and spin-gap states.

Contribution

First detailed exploration of magnetic ground state evolution in Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$ across a range of hole concentrations and magnetic fields.

Findings

Antiferromagnetic order stabilized for 0 ≤ x ≤ 1.3.

Spin-flop transition observed under magnetic field.

Spin-gap state forms at x=1.67 with ~1/3 hole per Cu.

Abstract

We have succeeded in growing large-size single-crystals of Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$ with $0 \le x \le 1.67$ and measured the magnetic susceptibility, specific heat and magnetization curve, in order to study the magnetic ground state in the edge-sharing CuO$_2$ chain as a function of hole concentration and magnetic field. In $0 \le x \le 1.3$, it has been found that an antiferromagnetically ordered phase with the magnetic easy axis along the b-axis is stabilized and that a spin-flop transition occurs by the application of magnetic fields parallel to the b-axis. The antiferromagnetic transition temperature decreases with increasing $x$ and disappears around $x =$ 1.4. Alternatively, a spin-glass phase appears around $x = 1.5$. At $x = 1.67$ where the hole concentration is $\sim$ 1/3 per Cu, it appears that a spin-gap state is formed owing to the formation of spin-singlet pairs. No sign of the coexistence of an antiferromagnetically ordered state and a spin-gap one suggested in Ca$_{1-x}$CuO$_2$ has been found in Ca$_{2+x}$Y$_{2-x}$Cu$_5$O$_{10}$.