Magnetic and thermal properties of a Haldane chain with one-dimensional ferromagnetic chains in square lattice

Since Haldane conjectured that ground state of one-dimensional Heisenberg antiferromagnet has a finite spin gap for integer spins, while gapless excitations for half-odd integer spins, it has inspired lots of theoretical and experimental studies on low-dimensional quantum magnets. Several one-dimensional chain systems of integer spins, so called Haldane chain, have been discovered and studied, such as CsNiCl₃, Y₂BaNiO₅, PbNi₂V₂O₈, SrNi₂V₂O₈, AgVP₂S₆. It has been known that most of the Haldane chain has antiferromagnetic coupling for the intrachain exchange interaction. Recently, we have found a Haldane chain compound in which antiferromagnetic order is accompanied by antiferromagnetic interchain coupling between one-dimensional ferromagnetic chains below 30.5 Kelvin. In this presentation, we present comprehensive study of its magnetic and thermal properties.