Anisotropy of magnetic interactions in the spin-ladder compound(C5H12N)2CuBr

Abstract

Magnetic excitations in the spin-ladder material (C5H12N)2CuBr4 [BPCB] are probed by highresolution multi-frequency electron spin resonance (ESR) spectroscopy. Our experiments provide a direct evidence for a biaxial anisotropy (∼ 5% of the dominant exchange interaction), that is in contrast to a fully isotropic spin-ladder model employed for this system previously. It is argued that this anisotropy in BPCB is caused by spin-orbit coupling, which appears to be important for describing magnetic properties of this compound. The zero-field zone-center gap in the excitation spectrum of BPCB, ∆0/kB = 16.5 K, is detected directly. Furthermore, an ESR signature of the inter-ladder exchange interactions is obtained. The detailed characterization of the anisotropy in BPCB completes the determination of the full spin hamiltonian of this exceptional spin-ladder material and shows ways to study anisotropy effects in spin ladders.

Statics and Dynamics of Weakly Coupled Antiferromagnetic Spin-1/2 Ladders in a Magnetic Field

“…The compound (C 5 H 12 N) 2 CuBr 4 , customarily called BPCB or (Hpip) 2 CuBr 4 , has been intensively investigated using different experimental methods such as NMR, 30 ND, 31 INS, 32,33 calorimetry, 29 magnetometry, 84 magnetostriction, 85,86 and electron-spin-resonance spectroscopy 87 …”

“…Small anisotropy of the couplings can exist and indeed are necessary to interpret recent ESR experiments. 87 Other terms, such as longer-range exchanges or Dzyaloshinskii-Moryia (DM) terms, might occur along the legs even if the latter is forbidden by symmetry along the dominant rung coupling. Clearly all these deviations from the Heisenberg model cannot be larger than a few percent.…”

“…Recently a slight anisotropy of the order of 5% of J ⊥ has been discovered by ESR 87 measurements. This anisotropy could explain the small discrepancies between the couplings found in different experiments.…”

Electron spin resonance shifts inS=1antiferromagnetic chains

“…In fact, thanks to this advantage of ESR, many interesting ESR experiments have been performed in onedimensional quantum spin systems under high magnetic field. [4][5][6] These recent precise ESR experiments highlights necessity of reliable quantitative theory of ESR in the field-induced critical phase.…”

“…Recently, dynamics of electron spins in the field-induced critical phases are actively investigated by various experimental techniques. [3][4][5] Among these experimental techniques, electron spin resonance (ESR) occupies a unique position in its sensitivity to interactions between electron spins. In fact, thanks to this advantage of ESR, many interesting ESR experiments have been performed in onedimensional quantum spin systems under high magnetic field.…”