Magnetic proximity-enhanced Curie temperature of Cr-dopedBi2Se3thin films

Abstract

We report a study on the transition temperature T C of Cr-doped topological insulator thin films, where an increase in the ferromagnetic onset can provide a pathway towards low-power spintronics in the future. Arrott plots, measured by surface-sensitive x-ray magnetic circular dichroism at the Cr L 2,3 edge as a function of field at various low temperatures, give a T C ≈ 7 K for the pristine surface. This is comparable to the bulk value of the film, which means that there is no indication that the spontaneous magnetization is different near the surface. Evaporation of a thin layer of Co onto the pristine surface of the in-situ cleaved sample increases the ordering temperature near the surface to ∼19 K, while in the bulk it rises to ∼10 K. X-ray absorption spectroscopy shows that Cr enters the Bi 2 Se 3 host matrix in a divalent state, and is unchanged by the Co deposition. These results demonstrate a straightforward procedure to increase the transition temperature of doped topological insulators.

Magnetic proximity coupling to Cr-doped Sb2Te3 thin films

“…In contrast, for bulk Cr x Bi 2−x Se 3 , as reported in Refs. [13,16], this second peak is much lower in intensity. It is important to note that this second peak is not due to oxidation.…”

“…The XMCD line shape of Cr x Sb 2−x Te 3 is very similar to that reported for bulk Cr x Bi 2−x Se 3 , including the small shoulder at 0.6 eV below the L 3 maximum and the characteristic sharp negative peak in the L 2 edge at 584.6 eV (see Refs. [13,16]). Note that despite the negative dip, the overall intensity of the Cr L 2 is still positive, and thus opposite to the L 3 edge, as imposed by the 2p spin-orbit coupling [31].…”

“…V-and Cr-doping of (Sb,Bi) 2 (Se,Te) 3 have proven to be some of the most promising ways of producing MTIs [12][13][14], allowing for the experimental verification of the QAHE [15]. For Cr-doped Bi 2 Se 3 , it has previously been demonstrated that the ferromagnetic transition temperature, T C , can be enhanced from 7-19 K through the deposition of a Co layer onto the surface of the MTI [16]. Despite this more than doubled T C it is still well below accessible temperatures for practical applications.…”

Topological quantum weak antilocalization limit and anomalous Hall effect in semimagnetic Bi2−xCrxSe3/Bi2Se3−yTey heterostructure

“…The binding energies that correspond to 3 + (2p) oxidation state of bulk Cr are 584 eV and 575 eV, which is smaller than our observed Cr (2p) values. The spin-orbit coupling strength gradually varied from Bi (4 f) to Cr (2p) as a consequence of the blue shift between them as well as large splitting of binding energy levels (∼9 eV) rather than Cr-Se bond contribution was observed [14]. From XPS, the electron doping effect on the surface caused by a residual atmospheric gas molecule absorption plays the major role for inducing charge transfer effect [32].…”

“…Magnetically coupled spin-orbit strength in non-magnetic topological insulators (MTI) pertain a major role for the rise of quantum anomalous Hall effect (QAHE) which is crucial for many potential applications [1][2][3][4][5][6][7][8][9][10][11][12]. To amend MTI, adding magnetic dopants into topological insulators (TIs) or putting TI adjacent to a magnetic layer have been adopted recently [13][14][15][16][17][18][19]. The latter one is called the proximity induced magnetism, which was demonstrated in Bi 2 Se 3 /YIG [20], Bi 2−x Cr x Se 3 /YIG [21], and Bi 2 Se 3 /EuS [22].…”