Coexistence of ferromagnetism and unconventional spin-glass freezing in the site-disordered kagome ferrite SrSn2Fe4O11

Abstract

Single-crystal x-ray diffraction refinements indicate SrSn 2 Fe 4 O 11 crystallizes in the hexagonal R-type ferrite structure with non-centrosymmetric space group P6 3 mc 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 SrSn 2 Fe 4 O 11 single crystals undergo ferro-or ferri-magnetic (FM) behavior below a transition temperature T C = 630 K with very low coercive fields μ ο H c⊥ = 0.27 Oe and μ ο H c⎟⎟ = 1.5 Oe at 300 K, for applied field perpendicular and parallel to the c-axis, respectively. The value for T C 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 Fe 3+ and nonmagnetic Sn 4+ 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 at 0.8 eV, consistent with observed semiconducting properties.

YbMgGaO4: A Triangular‐Lattice Quantum Spin Liquid Candidate

“…The broad hump is indeed observed at T s || ≈ 0.1 K when the measuring field of 0.01 T (≈1% J 0 /μ B / g ave ) is applied along the c axis, but it shifts to T s ┴ ≈ 0.2 K when the field is along the ab plane (see Figure c): T s || / T s ┴ ≈ J zz / J xx , where J xx = 2 J ± . If there is a transition, the critical temperature must keep direction independent . Second, no splitting between the ZFC and FC data is observed down to 40 mK, supporting the formation of the QSL GS, and consistent with the previously reported heat capacity and μSR results.…”

Rearrangement of Uncorrelated Valence Bonds Evidenced by Low-Energy Spin Excitations in YbMgGaO4

“…Such a direction dependence is not expected in a conven-tional freezing scenario, where the transition temperature should remain the same for all field directions [26,27], especially in the applied field as low as 0.01 T, two orders of magnitude smaller than [10], and the direction dependence of T s merely reflects the anisotropy of magnetic couplings, whereas the difference between χ and χ ⊥ is mostly due to the g-tensor anisotropy [25]. (ii) No splitting between the ZFC and FC data is observed down to 40 mK, |χ ZF C -χ F C |/(χ ZF C +χ F C ) < 2% ( Fig.…”

“…1(b)]. Such a direction dependence is not expected in a conven-tional freezing scenario, where the transition temperature should remain the same for all field directions [26,27], especially in the applied field as low as 0.01 T, two orders of magnitude smaller than J 0 [J 0 /(gµ B ) ∼ 1 T]. We recognize that T ⊥ s /T s ∼ J xx /J zz , where J xx = 2J ± ∼ 2 K and J zz ∼ 1 K [10], and the direction dependence of T s merely reflects the anisotropy of magnetic couplings, whereas the difference between χ and χ ⊥ is mostly due to the g-tensor anisotropy [25].…”

Probing the Griffiths like phase, unconventional dual glassy states, giant exchange bias effects and its correlation with its electronic structure in Pr2−x Sr x CoMnO6

“…As a matter of fact, in SG states, the competing FM/ AFM interactions tend to have equivalent strengths on lowering the temperature while the CG state evolves if one of the competing interactions (AFM or FM) is weaker relative to the other. However, the existence of the static-disorders in the system is often seen to be responsible for anticipating the short range magnetic ordering such as SG or CG states at lower temperatures in addition to the existing higher temperature long range magnetic ordering, known as re-entrant spin glass (RSG) or cluster glass (RCG) states [26][27][28]. This particular dynamic magnetic property recently has attracted immense research interest world-wide and remained at the forefront of research.…”

“…Eventually, as compared to the large number of systems exhibiting SG states, fewer systems are reported to show RSG or RCG states. The different theoretical and experimental investigations showed different possible mechanisms are associated to the observed glassiness viz., site disorder, geometrical spin frustration, spin-orbit interaction, octahedral tilting etc [8,[28][29][30][31][32]. However, the exact origin is still an open challenge and requires more efforts for a complete understanding.…”