Development of ferromagnetism in the doped topological insulatorBi2−xMnxTe3

Abstract

The development of ferromagnetism in Mn-doped Bi 2 Te 3 is characterized through measurements on a series of single crystals with different Mn content. Scanning tunneling microscopy analysis shows that the Mn substitutes on the Bi sites, forming compounds of the type Bi 2−x Mn x Te 3 , and that the Mn substitutions are randomly distributed, not clustered. Mn doping first gives rise to local magnetic moments with Curie-like behavior, but by the compositions Bi 1.96 Mn 0.04 Te 3 and Bi 1.91 Mn 0.09 Te 3 , a second-order ferromagnetic transition is observed, with T C ϳ 9 -12 K. The easy axis of magnetization in the ferromagnetic phase is perpendicular to the Bi 2 Te 3 basal plane. Thermoelectric power and Hall effect measurements show that the Mn-doped Bi 2 Te 3 crystals are p-type. Angle-resolved photoemission spectroscopy measurements show that the topological surface states that are present in pristine Bi 2 Te 3 are also present at 15 K in ferromagnetic Mn-doped Bi 2−x Mn x Te 3 and that the dispersion relations of the surface states are changed in a subtle fashion.

Ripple-modulated electronic structure of a 3D topological insulator

“…The single crystals of Bi 2 Te 3 used in this study were grown via a standard modified Bridgman method 36 . Bulk transport measurements show that the sample is p-type as expected.…”

Topological Insulator Materials

“…Mn-doping to Bi 2 Te 3 was reported to induce bulk ferromagnetism with Curie temperature of up to 12 K with 9% Mn doping. 245) For Bi 2 Se 3 , it was reported that Fe and Mn dopings do not induce bulk ferromagnetism, but they were found to open a small gap at the Dirac point in the surface Dirac cone, 246) possibly because of a ferromagnetic order that develops only on the surface. Such a Diracfermion-mediated ferromagnetism was confirmed in Mndoped Bi 2 (Se,Te) 3 thin flakes, in which the chemical potential was successfully tuned into the bulk band gap so that the anomalous Hall effect coming only from the surface electrons can be measured to probe their ferromagnetic order.…”

Signatures of Dirac fermion-mediated magnetic order

“…Although numerous studies aimed to shed light on the role played by magnetic perturbations, contradictory results have been obtained and a clear picture is still missing [16][17][18][19][20][21][22][23][24][25] . Results published so far seem to suggest that surface-and bulk-doped samples behave quite differently.…”