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 magnetic, specific heat and ESR measurements on a series of S = 1/2 spin ladder compounds Cu(Qnx)(Cl (1−x) Brx)2. Down to T = 2 K all the observables can be described by the spin ladder model with about 1% of S = 1/2 impurities in the background, which are present even in a nominally pure Cu(Qnx)Cl2 and Cu(Qnx)Br2, for the whole range of 0 ≤ x ≤ 1. We extract ladder exchange constants J l (x) and Jr(x) as well as the gap value ∆(x) by comparing the experimental data to quantum Monte-Carlo simulations. As the ESR measurements show the g-factor of impurities to be precisely equal to g-factor of the ladder spins, we suppose the impurities to be the consequence of structural defects resulting in a broken ladder ends.

We have studied electron spin resonance (ESR) absorption spectra for the non-magnetically diluted strong-leg spin ladder magnet (C7H10N)2Cu (1−x) ZnxBr4 (abbreviated as DIMPY) down to 450 mK. Formation of the clusters with non-zero net magnetization is confirmed, the cluster-cluster interaction is evidenced by the concentration dependence of ESR absorption. High temperature spin relaxation time was found to increase with non-magnetic dilution. The ESR linewidth analysis proves that the Dzyaloshinskii-Moriya interaction remains the dominant spin relaxation channel in diluted DIMPY. Experimental data indicate that the dilution results in the weakening of the effective Dzyaloshinskii-Moriya interaction, which can be interpreted as total suppression of DM interaction in the close vicinity of impurity atom.