Tunneling splitting of magnetic levels in Fe8 detected by 1H NMR cross relaxation

Measurements of proton NMR and the spin lattice relaxation rate 1/T1 in the octanuclear iron (III) cluster [Fe8(N3C6H15)6O2(OH)12][Br8 9H2O], in short Fe8, have been performed at 1.5 K in a powder sample aligned along the main anisotropy z axis, as a function of a transverse magnetic field (i.e., perpendicular to the main easy axis z). A big enhancement of 1/T1 is observed over a wide range of fields (2.5-5 T), which can be attributed to the tunneling dynamics; in fact, when the tunneling splitting of the pairwise degenerate m=+-10 states of the Fe8 molecule becomes equal to the proton Larmor frequency a very effective spin lattice relaxation channel for the nuclei is opened. The experimental results are explained satisfactorily by considering the distribution of tunneling splitting resulting from the distribution of the angles in the hard xy plane for the aligned powder, and the results of the direct diagonalization of the model Hamiltonian.Comment: J. Appl. Phys., in pres

Magnetisation of hole-doped CuO2 spin chains in Sr14-xCaxCu24O41

We report on magnetisation measurements of Sr14-xCaxCu24O41, with 0 <= x <= 12, in magnetic fields up to 16 T. The low temperature magnetic response of the CuO2 spin chains changes strongly upon doping. For x = 0, the ground state with nearly independent dimers is confirmed. Reduction of the number of holes in the chains through Ca-doping leads to an additional contribution to the magnetisation, which depends linearly on the magnetic field. Remarkably, the slope of this linear contribution increases with the Ca content. We argue that antiferromagnetic spin chains do not account for this behaviour but that the hole dynamics might be involved.Comment: In v2, spelling of author names has been change

Anomalous pressure effect on the remanent lattice striction of a (La,Pr)1.2_{1.2}Sr1.8_{1.8}Mn2_{2}O7_{7} bilayered manganite single crystal

We have studied the pressure effect on magnetostriction, both in the $ab$-plane and along the c-axis, of a (La,Pr)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ bilayered manganite single crystal over the temperature region where the field-induced ferromagnetic metal (FMM) transition takes place. For comparison, we have also examined the pressure dependence of magnetization curves at the corresponding temperatures. The applied pressure reduces the critical field of the FMM transition and it enhances the remanent magnetostriction. An anomalous pressure effect on the remanent lattice relaxation is observed and is similar to the pressure effect on the remanent magnetization along the c-axis. These findings are understood from the view point that the double-exchange interaction driven FMM state is strengthened by application of pressure.Comment: 7 pages,7 figure

Inhomogeneous electronic structure probed by spin-echo experiments in the electron doped high-Tc superconductor Pr_{1.85}Ce_{0.15}CuO_{4-y}

63Cu nuclear magnetic resonance (NMR) spin-echo decay rate (T_2^{-1}) measurements are reported for the normal and superconducting states of a single crystal of Pr_{1.85}Ce_{0.15}CuO_{4-y} (PCCO) in a magnetic field B_0=9T over the temperature range 2K<T<200K. The spin-echo decay rate is temperature-dependent for T<55K, and has a substantial dependence on the radio frequency (rf) pulse parameters below T~25K. This dependence indicates that T_2^{-1} is strongly effected by a local magnetic field distribution that can be modified by the rf pulses, including ones that are not at the nuclear Larmor frequency. The low-temperature results are consistent with the formation of a static inhomogeneous electronic structure that couples to the rf fields of the pulses.Comment: 4 pages, 4 figure

Steplike Lattice Deformation of Single Crystalline (La0.4_{0.4}Pr0.6_{0.6})1.2_{1.2}Sr1.8_{1.8}Mn2_{2}O7_{7} Bilayered Manganite

We report a steplike lattice transformation of single crystalline (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$bilayered manganite accompanied by both magnetization and magnetoresistive jumps, and examine the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator to a ferromagnetic metal phase accompanied by a huge decrease in resistance. Our findings support that the abrupt magnetostriction is closely related to an orbital frustration existing in the inhomogeneous paramagnetic insulating phase rather than a martensitic scenario between competing two phases.Comment: 5 pages,4figures, v4: figures are changed, in press in Phys.Rev.Let

Possible Magnetic Chirality in Optically Chiral Magnet [Cr(CN)6_6][Mn(SS)-pnH(H2_2O)](H2_2O) Probed by Muon Spin Rotation and Relaxation

Local magnetic fields in a molecule-based optically chiral magnet [Cr(CN)$_6$][Mn($S$)-pnH(H$_2$O)](H$_2$O) (GN-S) and its enantiomer (GN-R) are studied by means of muon spin rotation and relaxation (muSR). Detailed analysis of muon precession signals under zero field observed below T_c supports the average magnetic structure suggested by neutron powder diffraction. Moreover, comparison of muSR spectra between GN-S and GN-R suggests that they are a pair of complete optical isomers in terms of both crystallographic and magnetic structure. Possibility of magnetic chirality in such a pair is discussed.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp