Reinvestigation of spin-density wave of metallic Cr by neutron scattering-Search for a connection to stripe order--

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1. We characterized novel low-energy magnetic excitations of Cr, so-called Fincher-Burke mode (FB-mode), by neutron inelastic scattering. Surprisingly, both the magnetic-peak intensity and the magnetic-dispersion relation are found to be asymmetric about the magnetic-zone center. Another single crystal of Cr reproduces this prominent feature using different instrumental resolutions, and the asymmetry becomes less significant with increasing temperature. Thus, we concluded that such the asymmetry is an intrinsic nature of the FB mode, or that there is another factor governing this asymmetry (e. g. chirality). In order to investigate further, we tried to observe Mn/V-impurity effects on the FB mode. We succeeded in growing such the single crystals in 1-mm size by arc-melting techniques. By tuning the growing condition, it will be able to grow impurity-doped crystals up to 10 mm for inelastic neutron scattering experiments.2. Through Ni-impurity doping onto La2-xSrxCuO4 (LSCO), we found that carrier concentration governs magnetic correlations as well as electric transport. This is analogous to the case of impurity doping on Cr, in which the incommensurability of spin correlations is proportional to impurity concentration (or, band-electron density). However, no magnetic excitations like the FB mode in Cr are observable yet in LSCO. It is necessary to narrow an argument whether there are no such magnetic excitations intrinsically, the cross section is just small to detect, or S(Q, E) is quite different between Cr and LSCO.3. During the course of neutron-scattering research for Cr and LSCO, a high S/N ratio and a fine Q resolution are required in neutron spectrometer. We developed a new technique that uses a combination of a Ge monochromator and a pylorytic-graphite analyzer in inelastic scattering measurements. In fact, we succeeded in observing quasi-particle excitations, such as phonons and magnons, for Cr and LSCO with high Q resolutions and reasonable statistics.