Coexistence of Ferromagnetism and Unconventional Spin-Glass Freezing in the Site-Disordered Kagome Ferrite SrSn₂Fe₄O₁₁

Authors

L. Shlyk, Universität Stuttgart, Germany
S. Strobel, Universität Stuttgart, Germany
Barry Farmer, University of KentuckyFollow
Lance E. De Long, University of KentuckyFollow
R. Niewa, Universität Stuttgart, Germany

Abstract

Single-crystal x-ray diffraction refinements indicate SrSn₂Fe₄O₁₁ crystallizes in the hexagonal R-type ferrite structure with noncentrosymmetric space group P6₃mc and lattice parameters a = 5.9541(2)Å, c = 13.5761(5)Å, Z = 2 (R(F) = 0.034). Octahedrally coordinated 2a [M(1) and M(1a)] and 6c sites [M(2)] have random, mixed occupation by Sn and Fe; whereas the tetrahedrally coordinated 2b sites [Fe(3) and Fe(3a)] are exclusively occupied by Fe, whose displacement from the ideal position with trigonal-bipyramidal coordination causes the loss of inversion symmetry. Our dc and ac magnetization data indicate SrSn₂Fe₄O₁₁ single crystals undergo a ferro- or ferri-magnetic transition below a temperature T_C = 630 K with very low coercive fields μ_oH_c⊥ = 0.27 Oe and μ_oH_c∥ = 1.5 Oe at 300 K, for applied field perpendicular and parallel to the c axis, respectively. The value for TC is exceptionally high, and the coercive fields exceptionally low, among the known R-type ferrites. Time-dependent dc magnetization and frequency-dependent ac magnetization data indicate the onset of short-range, spin-glass freezing below T_f = 35.8 K, which results from crystallographic disorder of magnetic Fe³⁺ and nonmagnetic Sn⁴⁺ ions on a frustrated Kagome sublattice. Anomalous ac susceptibility and thermomagnetic relaxation behavior in the short-range-ordered state differs from that of conventional spin glasses. Optical measurements in the ultraviolet to visible frequency range in a diffuse reflectance geometry indicate an overall optical band gap of 0.8 eV, consistent with observed semiconducting properties.

Document Type

Article

Publication Date

2-23-2018

Notes/Citation Information

Published in Physical Review B, v. 97, issue 5, 054426, p. 1-11.

©2018 American Physical Society

The copyright holder has granted the permission for posting the article here.

Digital Object Identifier (DOI)

https://doi.org/10.1103/PhysRevB.97.054426

Funding Information

Research at the University of Kentucky was supported by US National Science Foundation Grant No. DMR-1506979.

Repository Citation

Shlyk, L.; Strobel, S.; Farmer, Barry; De Long, Lance E.; and Niewa, R., "Coexistence of Ferromagnetism and Unconventional Spin-Glass Freezing in the Site-Disordered Kagome Ferrite SrSn₂Fe₄O₁₁" (2018). Physics and Astronomy Faculty Publications. 582.
https://uknowledge.uky.edu/physastron_facpub/582