Magnetic ordering in Ho-doped Bi2Te3 topological insulator thin films

We investigate the magnetic properties of Ho-doped Bi2Te3 thin films grown by molecular beam epitaxy. Analysis of the polarized X-ray absorption spectra at the Ho M-5 absorption edge gives an effective 4f magnetic moment which is similar to 45% of the Hund's rule ground state value. X-ray magnetic circular dichroism (XMCD) shows no significant anisotropy, which suggests that the reduced spin moment is not due to the crystal field effects, but rather the presence of non-magnetic or antiferromagnetic Ho sites. Extrapolating the temperature dependence of the XMCD measured in total electron yield and fluorescence yield mode in a field of 7 T gives a CurieWeiss temperature of theta(CW) approximate to -30 K, which suggests antiferromagnetic ordering, in contrast to the paramagnetic behavior observed with SQUID magnetometry. From the anomaly of the XMCD signal at low temperatures, a Neel temperature T-N between 10 K and 25 K is estimated. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim