This paper presents results of experiment which studied (using the Nuclear-Orientation technique) the gamma-decay of isomeric Hf-180m. The described experiment used the newly developed mass-separated Hf-180m beam at ISOLDE, CERN which was implanted into an iron foil polarized at millikelvin temperatures. The observed irregular admixture of E2 to M2/E3 multipolarity in 501 keV 8(-) -> 6(+) gamma-transition was the clear experimental evidence for parity mixing in nuclear states. The temperature dependence of the forward-backward asymmetry of the angular distribution has been measured over extended range of temperatures (and therefore nuclear polarizations), proving a parity mixing of the 8(-) and 8(+) nuclear levels. The value found for the E2/M2 mixing ratio epsilon = -0.032(2) of this transition is in close agreement with averaged value of all previously published results epsilon = -0.030(2).