We investigate the order parameter of noncentrosymmetric superconductors Li2Pd3B and Li2Pt3B via the behavior of the penetration depth lambda(T). The low-temperature penetration depth shows BCS-like behavior in Li2Pd3B, while in Li2Pt3B it follows a linear temperature dependence. We propose that broken inversion symmetry and the accompanying antisymmetric spin-orbit coupling, which admix spin-singlet and spin-triplet pairing, are responsible for this behavior. The triplet contribution is weak in Li2Pd3B, leading to a wholly open but anisotropic gap. The significantly larger spin-orbit coupling in Li2Pt3B allows the spin-triplet component to be larger in Li2Pt3B, producing line nodes in the energy gap as evidenced by the linear temperature dependence of lambda(T). The experimental data are in quantitative agreement with theory.

We present a detailed magnetic study of the Pr 1/3 Ca 2/3 MnO 3 manganite, where we observe the presence of small ferromagnetic ͑FM͒ domains ͑diameter ϳ10 Å͒ immersed within the charge-ordered antiferromagnetic ͑AFM͒ host. Due to the interaction of the FM nanodroplets with a disordered AFM shell, the low-temperature magnetization loops present exchange bias ͑EB͒ under cooling in an applied magnetic field. Our analysis of the cooling field dependence of the EB yields an antiferromagnetic interface exchange coupling comparable to the bulk exchange constant of the AFM phase. We also observe training effect of the EB, which is successfully described in terms of a preexisting relaxation model developed for other classical EB systems. This work provides the first evidence of intrinsic interface exchange coupling in phase separated manganites.

Electron-spin-resonance (ESR) measurements are reported in the two-dimensional Heisenberg magnet K2MnF, and compared with a theory developed here. Results are in excellent agreement with calculated values and, we feel, give strong confirmation of recent theories of spin dynamics. The theory treats the linewidth hH and line shape in a two-dimensional Heisenberg system by assuming diffusive motion for the long-time dependence of the time correlation functions. The short-time dependence is taken to be Gaussian, and the resulting shortand long-time parts are joined together in a manner siniilar to that used by Gulley, Hone, Scalapino, and Silbernagel. An angular dependence roughly of the form AH~(3cos 8 -1) + (const. ) (8 is the angle of dc field with respect to the perpendicular to the plane) is observed at high temperature, as predicted by the theory. This angular dependence cannot be explained by either the secular or nonsecular parts of the second moment. Rather, it is due explicitly to the dominance of wave-vector q 0 modes in the long-time decay of correlations in a tw~imensional system. As temperature is lowered toward the antiferromagnetic ordering temperature T"=45 K, the linewidth initially decreases, passes through a minimum, and then increases rapidly near TN. The angular dependence is also temperature-dependent such that h,H(8 = %F) becomes less than~(8 = 5F} below about 65 K. These features of the temperature dependence are consistent with the theory. Indeed, we find absolute agreement between theory and experiment to within 20% or better at all angles over a broad range of temperature. The theory contains no adjustable parameters since classical dipolar coupling is taken as the sole source of broadening and we use the same exchange constant J as obtained from susceptibility measurements. The room-temperature line shape, which is Lorentzian at 8 = 55 and non-Lorentzian at 8 = 90', and the frequency dependence of hH, measured at 9.8 and 23.4 GHz, are also in agreement with theory. Shift of the resonance field with angle has been measured as well. This effect can be explained quantitatively by the net dipolar field and, contrary to the other phenomena, does not, in the main, reflect two-dimensional spin dynamics.

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