Spin wave resonances in antiferromagnets

Spin wave resonances with enormously large wave numbers corresponding to wave vectors 10^5-10^6 cm^{-1} are observed in thin plates of FeBO3. The study of spin wave resonances allows one to obtain information about the spin wave spectrum. The temperature dependence of a non-uniform exchange constant is determined for FeBO3. Considerable softening of the magnon spectrum resulting from the interaction of magnons, is observed at temperatures above 1/3 of the Neel temperature. The excitation level of spin wave resonances is found to depend significantly on the inhomogeneous elastic distortions artificially created in the sample. A theoretical model to describe the observed effects is proposed.Comment: 6 pages, 6 figure

Field and temperature dependence of the NMR relaxation rate in the magnetic quadrupolar liquid phase of spin-1/2 frustrated ferromagnetic chains

It is generally difficult to experimentally distinguish magnetic multipolar orders in spin systems. Recently, it was proposed that the temperature dependence of the nuclear magnetic resonance relaxation rate 1/T_1 can involve an indirect, but clear signature of the field-induced spin nematic or multipolar Tomonaga-Luttinger (TL) liquid phase [Phys. Rev. B79, 060406(R) (2009)]. In this paper, we evaluate accurately the field and temperature dependence of 1/T_1 in spin-1/2 frustrated J1-J2 chains combining field-theoretical techniques with numerical data. Our results demonstrate that isotherms of 1/T_1 as a function of magnetic field also exhibit distinctive non-monotonic behavior in spin nematic TL liquid, in contrast with the standard TL liquid in the spin-1/2 Heisenberg chain. The relevance of our results to quasi one-dimensional edge-sharing cuprate magnets, such as LiCuVO4, is discussed.Comment: 11 pages (2 column), 5 figures, published versio

Saturation field of frustrated chain cuprates: broad regions of predominant interchain coupling

An efficient and precise thermodynamic method to extract the interchain coupling (IC) of spatially anisotropic 2D or 3D spin-1/2 systems from their empirical saturation field H_s (T=0) is proposed. Using density-matrix renormalization group, hard-core boson, and spin-wave theory we study how H_s is affected by an antiferromagnetic (AFM) IC between frustrated chains described in the J_1-J_2-spin model with ferromagnetic 1st and AFM 2nd neighbor in-chain exchange. A complex 3D-phase diagram has been found. For Li2CuO2 and Y2Ca2Cu5O10, we show that H_s is solely determined by the IC and predict H_s approx 61 T for the latter.Using H_s approx 55 T from our high-field pulsed measurements one reads out a weak IC for Li2CuO2 close to that from neutron scattering.Comment: 4 pages, 6 figures, slightly revised version including a slightly changed title and abstract, one new figure and an EPAPS-supplementatary part have been adde