Perpendicular magnetic anisotropy of Tb magnetic moments in Tb/Fe multilayers

The direction of the magnetic moment of Tb in Fe(40 Angstrom)/Tb(x Angstrom) (x = 10 and 20) multilayers has been studied using the low-temperature nuclear orientation technique in the temperature range 5-50 mK and in the external magnetic field range B-ext = 0-8.5 T, with B-ext applied along the sample plane. The anisotropy of the 299 keV Tb-160 gamma-line was monitored in three directions with respect to B-ext and the sample plane. The perpendicular magnetic anisotropy (PMA) of the To magnetic moments has been found at zero B-ext for both systems. The PMA effect is increased when the Tb layers are thinner. An application of B-ext turned the Tb magnetic moments towards the sample plane, without reaching a full alignment even at B-ext = 8.5 T.