Experimental phase diagram of Cu2(C5H12N2)2Cl4: A quasi-one-dimensional antiferromagnetic spin- Heisenberg ladder

Abstract

Using magnetization, susceptibility, and spin resonance techniques, three distinct magnetic phases of ${\mathrm{Cu}}_2$(${\mathrm{C}}_5$ ${\mathrm{H}}_{12}$ ${\mathrm{N}}_2$ ${)}_2$ ${\mathrm{Cl}}_4$, a spin- ladder, are identified at zero temperature. For magnetic fields below ${\mathrm{H}}_{\mathrm{c}1\mathrm{}}$=7.5 T, the one-dimensional ground state is a valence-bond ordered singlet separated from a triplet band by an energy gap ${\mathrm{\Delta }}_1$/${\mathrm{k}}_{\mathrm{B}}$≈g${\mathrm{\mu }}_{\mathrm{B}}$ ${\mathrm{H}}_{\mathrm{c}1\mathrm{}}$/${\mathrm{k}}_{\mathrm{B}}$=10.8 K. For ${\mathrm{H}}_{\mathrm{c}1\mathrm{}}$<H<${\mathrm{H}}_{\mathrm{c}2\mathrm{}}$=13.2 T, the ground state is probably an antiferromagnetic canted or incommensurate state, and above ${\mathrm{H}}_{\mathrm{c}2\mathrm{}}$ the ground state is ferromagnetic. The exchange parameters used to parametrize the magnetic Hamiltonian are determined.