The magnetic phase diagram of the itinerant-electron-type helical-spin-glass re-entrant magnet Cr_0.81Mn_0.19Ge

The magnetic phase diagram of an itinerant-electron-type helical-spin-glass re-entrant magnet, Cr_0.81Mn_0.19Ge, is determined on the basis of measurements of the alternating-current (ac) susceptibility and magnetoresistivity in transverse and longitudinal fields, which are sensitive to the magnetic response of each spin component of the modulated spin ordering. The phase boundary line is essentially the same as that of typical itinerant-electron-type helical magnets, except for the appearance of spin-glass behaviour at low temperatures. The transverse ac susceptibility provides evidence of the coexistence of modulated spin order and spin-glass behaviour in the low-temperature phase, where spin freezing appears in the transverse component of the modulated spin structure. This is consistent with the mean-field picture of the vector spin glass.