The magnetic properties of a polycrystalline Sr3NiIrO6 sample have been investigated by means of susceptibility and magnetization measurements. On the one hand, it is found that this compound, made of magnetic chains on a triangular lattice, behaves very similarly to Ca3CoRhO6 and Ca3CoIrO6. In particular, at low temperature (T

We present a high-field magnetization study of the S=1/2 antiferromagnetic Heisenberg chain [PM Cu(NO3)2(H2O)2]n. For this material, as result of the Dzyaloshinskii-Moriya interaction and a staggered g-tensor, the ground state is characterized by an anisotropic field-induced spin excitation gap and a staggered magnetization. Our data reveal the qualitatively different behavior in the directions of maximum and zero spin excitation gap. The data are analyzed via exact diagonalization of a linear spin chain with up to 20 sites and on basis of the Bethe ansatz equations, respectively. For both directions we find very good agreement between experimental data and theoretical calculations. We extract the magnetic coupling strength J/kB along the chain direction to 36.3(5) K and determine the field dependence of the staggered magnetization component ms.PACS numbers: 75.10. Jm, 75.50.Ee, 75.30.Gw, 75.50.Xx Motivated by the rich variety of different magnetic ground states, such as quantum critical behavior or gaps in the spin excitation spectra, quasi-one-dimensional quantum magnets have been the focus of intense experimental and theoretical research efforts in recent years 1,2,3,4 . To gain deeper insight into the physics of such quantum spin systems well-defined model compounds need to be explored. Here, the uniform S = 1/2 antiferromagnetic Heisenberg chain (AFHC) is of particular interest, since it is exactly solvable using the so-called Bethe ansatz equations 5,6,7 . In S = 1/2 AFHCs, lacking inversion symmetry, additional terms in the Hamiltonian have to be taken into account, that is the Dzyaloshinskii-Moriya (DM) interaction and an alternating g tensor 8,9 . This gives rise to an effective staggered field h s perpendicular to the applied magnetic field H. Then the Hamiltonian is written aswith J as the coupling constant, h u = gµ B H/J as the effective uniform field, and h s the induced effective staggered field. In the following we refer to this as the staggered S = 1/2 AFHC model. Resulting from this extension of the uniform S = 1/2 AFHC are the opening of an anisotropic spin excitation gap with application of a magnetic field and new, particlelike excitations such as solitons, antisolitons, and their bound state, the "breather" 10,11 . Moreover, by fully evaluating the effect of the DM interaction on the ground state properties, a crossover to a qualitatively different high-field behavior has been predicted recently 12 .The model for the staggered S = 1/2 AFHC has been used to describe two materials in particular, copper benzoate 3 and copper pyrimidine nitrate [PM Cu(NO 3 ) 2 (H 2 O) 2 ] n 13 . For the latter compound, from a single-crystal study a magnetic exchange parameter J/k B = 36 K is derived. Further, an additional Curie-like contribution to the magnetic susceptibility at low temperatures is observed, which varies strongly with magnitude and direction of the applied external field. Specificheat measurements in magnetic fields verify the predicted formation of an anisotropic spin excitation gap, whos...

We report an electron spin resonance (ESR) study of the s = 1/2-Heisenberg pseudo-ladder magnet CaCu 2 O 3 in pulsed magnetic fields up to 40 T. At sub-Terahertz frequencies we observe an ESR signal originating from a small amount of uncompensated spins residing presumably at the imperfections of the strongly antiferromagnetically correlated host spin lattice. The data give evidence that these few percent of "extra" spin states are coupled strongly to the bulk spins and are involved in the antiferromagnetic ordering at T N = 25 K. By mapping the frequency/resonance field diagram we have determined a small gap for magnetic excitations below T N of the order of ∼ 0.3 − 0.8 meV. Such a small value of the gap explains the occurrence of the spin-flop transition in CaCu 2 O 3 at weak magnetic fields µ 0 H sf ∼ 3 T. Qualitative changes of the ESR response with increasing the field strength give indications that strong magnetic fields reduce the antiferromagnetic correlations and may even suppress the long-range magnetic order in CaCu 2 O 3 . ESR data support scenarios with a significant role of the "extra" spin states for the properties of lowdimensional quantum magnets.

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