Magnetic properties of a quantum spin ladder in proximity to the isotropic limit

Abstract

We report on the synthesis, crystal structure, magnetic, thermodynamic, and electron-spinresonance (ESR) properties of the coordination complex [Cu2(pz)3(4-HOpy)4](ClO4)4 [pz = pyrazine; 4-HOpy = 4-hydroxypyridine]. This material is identified as a spin-1/2 Heisenberg ladder system with exchange-coupling parameters Jrung/kB = 12.1(1) K and J leg /kB = 10.5(3) K [Jrung/J leg = 1.15(4)]. For single crystals our measurements revealed two critical fields, µ0Hc1 = 4.63(5) T and µ0Hc2 = 22.78(5) T (for H ∥ a * ), separating the gapped spin-liquid, gapless Tomonaga-Luttinger-liquid, and fully spin-polarized phase. No signature of a field-induced transition into a magnetically ordered phase was found at temperatures down to 0.5 K. The material bridges an important gap by providing an excellent physical realization of an almost isotropic spin-1/2 strong-rung Heisenberg ladder system with modest exchange-coupling energy and critical-field scales.

Approaching the isotropic spin-ladder regime: structure and magnetism of all-pyrazine-bridged copper(ii)-based antiferromagnetic ladders

“…The antiferromagnetic exchange through the pyrazine linkages is typical of copper(II) complexes as the superexchange strength through pyrazine usually varies from −5 to −18 K. 16,[30][31][32]43,48 The J rail /J rung ratio derived from the fits to the strong-rung ladder model shows that these two complexes exhibit nearly isotropic exchange (1: 0.867, [1.02]; 2: 0.946, [0.978]; the fits from χT (T ) are shown in brackets). Given the structure of the complexes, being approximately 4 + 2 with the elongation axis perpendicular to the Cu-pyrazine coordination plane, the two types of bridging pyrazine molecules are bonded through the d x 2 −y 2 orbital of the copper(II) ion much like the pyrazine bridged layers with less than four-fold symmetry which also give nearly square or square interactions.…”

“…We recently reported the serendipitous preparation of the first all-pyrazine bridged ladder, [Cu 2 (pz) 3 (4-HOpy) 4 ](ClO 4 ) 4 [4-HOpy = 4-hydroxypyridine]. 32 The compound exhibits a J rail / J rung ratio of 0.87, placing it among the most isotropic ladders reported, but with modest exchange strengths allowing for ready study over the full phase diagram. However, given the unexpected nature of the original synthesis, there was a question of whether a family of such materials could be prepared with variable J rail / J rung ratios allowing for detailed studies near the quantum critical point.…”