Magnetodielectric effect and spin state of iron ions in iron-substituted bismuth pyrostannate
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Magnetodielectric effect and spin state of iron ions in iron-substituted bismuth pyrostannate Lubov Udod1,2,a , Sergey Aplesnin1,2 , Maxim Sitnikov2 , Oxana Romanova1, Oleg Bayukov1, Alexander Vorotinov1, Dmitriy Velikanov1, Gennadiy Patrin1,3 1 Federal Research Center KSC SB RAS, Kirensky Institute of Physics, Akademgorodok 50, Krasnoyarsk,
Russia 660036
2 Siberian State University of Science and Technology, Krasnoyarsk, Russia 660037 3 Siberian Federal University, Krasnoyarsk, Russia 660041
Received: 1 April 2020 / Accepted: 16 September 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The magnetic and magnetodielectric properties of bismuth pyrostannate Bi2 (Sn1−x Fex )2 O7 (x = 0.1 and 0.2) have been examined. Using the Mössbauer spectroscopy and electron paramagnetic resonance, the high-spin state and crystallographic positions of iron ions have been established. The coexistence of triclinic symmetry domains in the Bi2 (Sn1−x Fex )2 O7 (x = 0.1) compound with the monoclinic symmetry below 140 K has been found. For the Bi2 (Sn1−x Fex )2 O7 composition with x = 0.2, the nonlinear field dependence of magnetization in the paramagnetic region up to room temperatures has been observed. The electric polarization hysteresis and the magnetoelectric effect in the Bi2 (Sn1−x Fex )2 O7 compound have been disclosed. The magnetic field-dependent anomalous behavior of magnetization has been explained by the magnetoelectric effect.
1 Introduction The compounds with a pyrochlore structure undergo the structural, magnetic, and ferroelectric phase transitions, which are usually accompanied by abrupt changes in the dielectric, mechanical, optical, and other properties [1]. Bismuth pyrostannate Bi2 Sn2 O7 belongs to the family of pyrochlores, in which spin ice is implemented, similar to the Ho2 Ti2 O7 , Dy2 Ti2 O7 , and other compounds [2,3]. In these materials, magnetic ions are located at the vertices of a three-dimensional grid of regular tetrahedra. Due to the strong anisotropy, the magnetic moments can be directed either toward the center of each tetrahedron or in the reversed direction. The magnetic moments have three nearest neighbors with frustrated exchange couplings. Bismuth pyrostannate is a dielectric. Substitution of iron for tin causes the magnetic ordering in the Bi2 Sn2 O7 compound and, due to the interaction between the magnetic and ferroelectric subsystems, one can expect the manifestation of the magnetoelectric effect. Iron ions in the Bi2 (Sn1−x Fex )2 O7 compound can induce crystal structure distortions and a shift of the temperature of the phase transition. In particular, the heterovalent substitution of tin ions for 3d elements changes the temperature of the α → β transition in Bi2 Sn2 O7 [4–7]. The
a e-mail: [email protected] (corresponding author)
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isovalent substitution of Bi3+ for Y3+ stabilizes the β phase at room temperature and normal pressure [8]. In iron
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