We report on the discovery of a novel triangular phase regime in the system La1-xSrxMnO3 by means of electron spin resonance and magnetic susceptibility measurements. This phase is characterized by the coexistence of ferromagnetic entities within the globally paramagnetic phase far above the magnetic ordering temperature. The nature of this phase can be understood in terms of Griffiths singularities arising due to the presence of correlated quenched disorder in the orthorhombic phase.

We report an electron spin resonance (ESR) study on single crystals of the heavy fermion metal YbRh2Si2 which shows pronounced non-Fermi liquid behavior related to a close antiferromagnetic quantum critical point. It is shown that the observed ESR spectra can be ascribed to a bulk Yb3+ resonance. This is the first observation of ESR of the Kondo ion itself in a dense Kondo lattice system. The ESR signal occurs below the Kondo temperature (T(K)) which thus indicates the existence of large unscreened Yb3+ moments below T(K). We observe the spin dynamics as well as the static magnetic properties of the Yb3+ spins to be consistent with the results of nuclear magnetic resonance and magnetic susceptibility.

We present a systematic electron-spin-resonance ͑ESR͒ study in single crystals of La 1Ϫx Sr x MnO 3 (0рx р0.2). The temperature dependence of the ESR linewidth marks all significant transitions between both orthorhombic (OЈ,O) and the rhombohedral ͑R͒ structural phases of the T-x phase diagram. All significant peculiarities of the ESR spectra for low x values within the OЈ phase can be attributed to the cooperative Jahn-Teller effect on the Mn 3ϩ e g states and to the influence of the Dzyaloshinsky-Moriya exchange interaction. Possible relaxation mechanisms at higher doping levels are discussed.

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