MU-SR AND ESR INVESTIGATIONS OF CUPRIC OXIDE

A polycrystalline high-purity CuO sample is investigated by mu SR and ESR methods. A phase transition to a magnetically ordered state below 227 K is observed in mu SR measurements in a transverse field. A struc ture in the temperature dependence of the fast component of muon-spin relaxation near commensurate-incommensurate phase transition is reveal ed in zero-magnetic-field mu SR measurements. Multifrequency precessio n is observed in the commensurate phase below 213 K. With increasing t emperature, this precession transforms into a one-frequency mode. This may be due to the fast tunneling of muons between two equivalent crys tallographic sites. Larmor precession is not detected in the incommens urate phase because of large damping. Data from ESR measurements indic ate that exchange interactions play an important role in cupric oxide.