Pis’ma v ZhETF, vol. 109, iss. 7, pp. 479 - 480

April 10

To the intrinsic magnetism of the Bi_1.08Sn_0.02Sb_0.9Te₂S topological

insulator

V. Sakhin⁺, E. Kukovitsky⁺, A. Kiiamov^∗, R. Khasanov^×, Yu. Talanov⁺, G. Teitel’baum⁺¹⁾

⁺Kazan E. K. Zavoisky Physical-Technical Institute of Russian Academy of Sciences, 420029 Kazan, Russia

^∗Institute of Physics, Kazan Federal University, 420008 Kazan, Russia

^×Paul Scherrer Institute, 5232 Villigen, Switzerland

Submitted 11 December 2018

Resubmitted 4 February 2019

Accepted 12

February 2019

DOI: 10.1134/S0021364019070014

Topological insulators (TI) belong to a class of quan-

discuss another origin of magnetism in the topological

tum materials [1-3] which are characterized by gap-

insulators, that is the creation of magnetic moment due

less surface states with Dirac-like dispersion. Their non-

to intrinsic nonmagnetic defects.

trivial topology is protected by time-reversal symmetry

The recent first-principles calculations [9, 10] demon-

(TRS). The violation of this symmetry gives rise to dif-

strate that for basic TI compounds Bi₂Te₃ and Bi₂Se₃

ferent topological states corresponding to new quantum

such local moments may be induced due to the anti-

materials. One of the most promising ways to study the

site substitutional defects in Te(Se) layer of the typi-

effects of TRS violation is the external doping of TI with

cal quintuple structure when some of the Te(Se) atoms

magnetic ions. While at low doping TI remain stable to

are replaced by the Bi atoms. The corresponding local

such perturbations, at higher doping a kind of ferromag-

magnetic moment’s value is about 0.6µ_B and it origi-

netic ordering takes place [4] and the TRS is broken due

nates from the p-orbital of the guest Bi atom. Such a

to appearance of the spontaneous magnetization. The

mechanism, which is different from that of a vacancy

magnetic ordering of the doped ions is driven by their in-

defect, provides new insights into the origins of mag-

direct Ruderman-Kittel-Kasuya-Yosida (RKKY) cou-

netism. Quite recently the intrinsic magnetic moments

pling via the charge carriers. Among the important con-

were found [11] in newer representative of bismuthates’

sequences of such ordering is realization of the quantum

family - Bi_1.08Sn_0.02Sb_0.9Te₂S (BSSTS) [12], which is

anomalous Hall effect, associated with the breaking of

recognized to be one of the best 3D topological insu-

TRS by magnetic ions doped into Bi₂Te₃ family of TI.

lators. The current paper is aimed on the ESR spec-

In addition, Bi₂Te₃ is predicted to serve as a platform

troscopy and the Superconducting Quantum Interfer-

for novel Majorana fermions detection once magnetism

ence Device (SQUID) magnetometry of the intrinsic

is introduced [5].

magnetic phase of TI basing on the example of this com-

The emergence of magnetism in TI has largely re-

pound.

lied upon the doping of external magnetic ions. There-

Using ESR spectroscopy together with the SQUID

fore the intense studies of extrinsic magnetic moments

magnetometry we found that the intrinsic magnetic mo-

were carried out with a help of Electron Spin Resonance

ments, originating from the nonmagnetic structural de-

(ESR) of the doped Mn ions serving as a sensitive spin

fects of Bi_1.08Sn_0.02Sb_0.9Te₂S topological insulator form

probes in the Bi₂Te₃ structure, where they occupy the

the superparamagnetic state. It represents an array of

positions of Bi ions. The critical behavior of the ESR

nanoscale single domain ferromagnets randomly dis-

signal in the vicinity of 10 K at cooling of Bi_2-xMn_xTe₃

tributed in the nonmagnetic media. Their net magnetic

compound for x = 0.05 confirmed the magnetic order-

polarization in the absence of external magnetic field

ing of Mn ions at this temperature [6, 7]. The similar

is completely averaged out and the time-reversal sym-

spectrum was observed for Bi_1.91Mn_0.09Te₃ with higher

metry is not violated. Single domain ferromagnetic par-

T_c of 12-13 K [8]. These studies confirming the violation

ticles at elevated temperatures behave magnetically in

of the time reversal symmetry of TI were restricted by

a manner analogous to the Langevin paramagnetism of

the external magnetic moments. In the current paper we

moment bearing atoms. The main distinction is that

the moment of the particle may be 10²-10³ times the

¹⁾e-mail: grteit@kfti.knc.ru

atomic moment.

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2019

479

480

V. Sakhin, E. Kukovitsky, A. Kiiamov et al.

The preparation of single crystals for TI studies

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7. Yu. Talanov, V. Sakhin, E. Kukovitskii, N. Garif’yanov,

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2019