Evolution of the ESR absorption in a strong-leg spin ladder magnet (C7H10N2)2CuBr4 (abbreviated as DIMPY) is studied from 300 K to 400 mK. Temperature dependence of the ESR relaxation follows a staircase of crossovers between different relaxation regimes. We ague that the main mechanism of ESR line broadening in DIMPY is uniform Dzyaloshinskii-Moria interaction (|D| = 0.20 K) with an effective longitudinal component along an exchange bond of Cu ions within the legs resulting from the low crystal symmetry of DIMPY and nontrivial orbital ordering. The same DzyaloshinskiiMoriya interaction results in the lifting of the triplet excitation degeneracy, revealed through the weak splitting of the ESR absorption at low temperatures.

We report on electron spin resonance (ESR) studies of the spin relaxation in Cs2CuCl4. The main source of the ESR linewidth at temperatures T ≤ 150 K is attributed to the uniform DzyaloshinskiiMoriya interaction. The vector components of the Dzyaloshinskii-Moriya interaction are determined from the angular dependence of the ESR spectra using a high-temperature approximation. Both the angular and temperature dependence of the ESR linewidth have been analyzed using a selfconsistent quantum-mechanical approach. In addition analytical expressions based on a quasiclassical picture for spin fluctuations are derived, which show good agreement with the quantumapproach for temperatures T ≥ 2J/kB ≈ 15 K. A small modulation of the ESR linewidth observed in the ac-plane is attributed to the anisotropic Zeeman interaction, which reflects the two magnetically nonequivalent Cu positions.

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