Partial antiferromagnetism in spin-chain Sr5Rh4O12, Ca5Ir3O12 and Ca4IrO6 single crystals

TL;DR

This study investigates the magnetic and structural properties of three quasi-one-dimensional insulators with triangular spin chains, revealing partial antiferromagnetic order, magnetic frustration, and complex magnetic transitions in single crystals.

Contribution

It provides new insights into the magnetic behavior and frustration effects in Sr5Rh4O12, Ca5Ir3O12, and Ca4IrO6, including detailed characterization of their magnetic phases and transitions.

Findings

Sr5Rh4O12 exhibits antiferromagnetic order below 23 K with Ising character.

Ca5Ir3O12 and Ca4IrO6 show antiferromagnetic order below 7.8 K and 12 K, respectively.

Ca5Ir3O12 involves only Ir4+ spins in magnetic ordering, with Ir5+ spins remaining disordered.

Abstract

We report a structural, thermodynamic and transport study of the newly synthesized Sr5Rh4O12, Ca5Ir3O12 and Ca4IrO6 single crystals. These quasi-one-dimensional insulators consist of a triangular lattice of spin chains running along the c-axis, and are commonly characterized by a partial antiferromagnetic (AFM) order, a small entropy removal associated with the phase transitions and a sizable low-temperature specific heat linearly proportional to temperature. Sr5Rh4O12 is defined by an AFM order below 23 K with strong evidence for an Ising character and two step-like transitions in isothermal magnetization leading to a ferrimagnetic state at 2.4 T and a ferromagnetic state at 4.8 T, respectively. Ca5Ir3O12 and Ca4IrO6 are also antiferromagnetically ordered below 7.8 K and 12 K, respectively, and show an unusually large ratio of the Curie-Weiss temperature to the Neel temperature. In particular, Ca5Ir3O12, which includes both Ir4+ and Ir5+ ions, reveals that only S=1/2 spins of the Ir4+ ions are involved in the magnetic ordering whereas S=3/2 spins of the Ir5+ ions remain disordered. All results suggest the presence of the geometrical frustration that causes incomplete long-range AFM order in these quasi-one-dimensional compounds.