Phase diagram and magnetic relaxation phenomena in Cu sub(2) OSeO sub(3)

We present an investigation of the magnetic-field-temperature phase diagram of Cu sub(2) OSeO sub(3) based on dc magnetization and ac susceptibility measurements covering a broad frequency range of four orders of magnitude, from very low frequencies reaching 0.1 Hz up to 1 kHz. The experiments were performed in the vicinity of T sub()c58.2 K and around the skyrmion lattice A phase. At the borders between the different phases the characteristic relaxation times reach several milliseconds and the relaxation is nonexponential. Consequently the borders between the different phases depend on the specific criteria and frequency used and an unambiguous determination is not possible.