Potential Skyrmion Host Fe(IO₃)₃: Connecting Stereoactive Lone-Pair Electron Effects to the Dzyaloshinskii-Moriya Interaction

Abstract

Magnetic skyrmions, which are topologically distinct magnetic spin textures, are gaining increased attention for their unique physical properties and potential applications in spintronic devices. Here we present a design strategy for skyrmion host candidates based on combinations of magnetic spin, asymmetric building units having stereoactive lone-pair electrons, and polar lattice symmetry. To demonstrate the viability of the proposed rational design principles, we successfully synthesized a Fe­(IO3)3 polycrystalline sample and single crystals by using a new simplified low-temperature pathway, which is experimentally feasible for extending materials growth of transition metal iodates. Single crystal X-ray and powder synchrotron X-ray diffraction measurements demonstrated that Fe­(IO3)3 crystallizes in the polar chiral hexagonal lattice with space group P63. The combined structural features of the macroscopic electric polarization along the c-axis stemming from the coalignment of the stereoactive lone-pairs of the IO3 – trigonal pyramid and the magnetic Fe3+ cation residing on the 3-fold rotation axis were selected to promote asymmetric exchange coupling. We find evidence of a predicted skyrmion phase at 14 K ≤ T ≤ 16 K and 2.5 T ≤ μ0 H ≤ 3.2 T driven by a Dzyaloshinskii–Moriya (DM) interaction, a conclusion supported by the appreciable DM exchange and the zero-field spiral antiferromagnetic ground state of Fe­(IO3)3 deduced from neutron diffraction experiments. The associated magnetic modulation wavelength of the putative skyrmions is expected to be short ∼18 nm, comparable to the period of the DM-driven incommensurate order. This work links stereoactive lone-pair electron effects to enhanced DM interaction, demonstrating a new approach for chemical guidelines in the search for skyrmionic states of matter.

Study of Integer Spin S = 1 in the Polar Magnet β-Ni(IO3)2

“…The I-O bond lengths range from 1.76(3) Å-1.85(4) Å. The subtle distortion of NiO 6 octahedra is likely induced by the packing effect of the (IO 3 ) − asymmetric building units [7,12,16].…”

“…Polar asymmetric anions with stereo-active lone-pair electrons such as (SeO 3 ) 2− and (IO 3 ) − trigonal pyramids provide avenues for accessing NCS polar structures, facilitated by the second-order Jahn–Teller distortion [ 6 , 11 , 12 , 13 , 14 , 15 ]. The presence of stereo-active lone-pair electrons and strong spin-orbit coupling from the heavy element (Se, I) in these asymmetric units have been shown to enhance Dzyaloshinskii-Moriya (DM) interaction [ 3 , 16 ].…”

“…Increased asymmetric exchange interactions in polar magnets with half-integer spins such as Cu 2 OSeO 3 (Cu 2+ , d 9 , 2 D ), Fe(IO 3 ) 3 (Fe 3+ , d 5 , 6 S ), and VOSe 2 O 5 (V 4+ , d 1 , 2 D ) have been demonstrated [ 2 , 16 , 17 ]; however, studies in integer spin systems featuring the DM interaction have been left unexplored. This is, in part, because there are relatively few integer spin magnets to investigate that have NCS polar lattice symmetries.…”

“…The I-O bond lengths range from 1.76(3) Å -1.85(4) Å . The subtle distortion of NiO6 octahedra is likely induced by the packing effect of the (IO3) − asymmetric building units[7,12,16].The polar symmetry of β-Ni(IO3)2 results largely from the alignment and addition of the (IO3) − local dipole along the b axis (Figure2a) [12,13]. FTIR spectra of β-Ni(IO3)2 show four absorption bands corresponding to four fundamental I-O vibrations expected for the (IO3) − group in C3v symmetry Γvib = 2A1 + 2E (Figure1b).…”

Spin and Orbital Effects on Asymmetric Exchange Interaction in Polar Magnets: M(IO3)2 (M = Cu and Mn)

“…2 In Fe(IO 3 ) 3 , a combination of stereoactive lone-pair electron effects and C 3 magnetic cations symmetry was proposed to work in favor of improved DM exchange. 29 Yet, compounds with the point group of D 2d and C 4v , in which 3-fold symmetry is absent, display unique characters concerning asymmetric DM interactions, thus hosting antiskyrmion and Neel skyrmion as exemplified in Mn 1.4 Pt 0.9 Pd 0.1 Sn and VOSe 2 O 5 , respectively. 11,30 However, due to the scarcity of systematic studies of polar magnets featuring enhanced or hindered DM exchange, synthetic tunability of spin properties, deterministic engineering of orbital contribution, and demonstration of how the coupled spin and orbital degrees of freedom drive the potential emergence of vortex-like spin textures still remain outstanding goals.…”