Magnetic ordering in Ho-doped Bi2Te3 topological insulator

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 M5 absorption edge gives an effective 4f magnetic moment which is ∼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 Curie–Weiss temperature of ϑCW ≈ –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 Néel temperature TN between 10 K and 25 K is estimated. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) The authors report the experimental discovery of an antiferromagnetic topological insulator thin film system. They have recently successfully synthesized high quality Ho‐doped Bi2Te3 thin films by molecular beam epitaxy and found paramagnetic bulk behavior of the film. Here, they present a surface‐sensitive X‐ray magnetic circular dichroism study at lower temperatures. At temperatures below ∼25 K they found a departure from the Curie law, pointing towards the existence of antiferromagnetic ordering.