Magnetic fields acting on muons in textured and single crystalline holmium

The mu SR method was used to measure the internal magnetic fields at interstitial sites of the crystal lattice in holmium, where muons are localized. In a simple helicoid structure all interstitial sites are magnetically equivalent, and thus in a mu SR experiment only one muon-spin precession frequency should be observed at a given temperature. In the spin-slip structure, the interstitial fields in different sections of the helicoid are different and the frequency spectrum of the muon signal should be more complicated. Most of the ZF mu SR measurements were performed on a holmium polycrystal with distinct texture. High-statistics ZF measurements below the Neel temperature were performed also on a holmium single crystal at several temperatures. The experimental spectrum was well described by a single frequency. This fact characterized the magnetic structure of holmium as a simple spiral. At the same time, the high values of the relaxation rate (up to 60 mu s exp -1 at 10K), could be due to overlapping of several frequencies.