A new layered triangular antiferromagnet Li₄FeSbO₆: spin order, field-induced transitions and anomalous critical behavior

Abstract

Structure, electrochemical, magnetic and resonance properties of new layered antimonate Li(4)FeSbO(6) were comprehensively studied using powder X-ray diffraction, cyclic voltammetry, magnetic susceptibility, heat capacity, electron spin resonance and Mössbauer spectroscopy. In the crystal structure the iron ions form the triangular network within (LiFeSbO(6))(3-) layers alternating with nonmagnetic lithium layers. The electrochemical activity studied implies an Fe(3+)/Fe(4+) redox couple at 4.3 V (ox.) and 3.9 V (red.) thereby revealing that Li can be reversibly extracted. The long-range antiferromagnetic order was found to occur at the Néel temperature, T(N) ≈ 3.6 K, confirmed both by the magnetic susceptibility data and specific heat ones. The effective magnetic moment is estimated to be 5.93 μ(B)/f.u. and satisfactorily agrees with theoretical estimations assuming high-spin configuration of Fe(3+) (S = 5/2). In the magnetically ordered state, though, the magnetization demonstrates rather peculiar behavior. An additional anomaly on the M(T) curves appears at T(2) < T(N) in moderate magnetic field. The positions of transitions at T(N) and T(2) separate increasingly with increasing external field. Multiple measurements consistently demonstrated field-sensitive moving of magnetic phase boundaries constituting a unique phase diagram for the compound under study. The complex low-dimensional (2D) nature of magnetic coupling was confirmed by the dynamic magnetic properties study. Electron spin resonance from Fe(3+) ions in paramagnetic phase is characterized by a temperature independent effective g-factor of 1.99 ± 0.01. However, the distortion and broadening of the ESR line were found to take place upon approaching the magnetically ordered state from above. The divergence of the temperature-dependent linewidth is analyzed in terms of both critical behavior close to long-range magnetic order and the Berezinskii-Kosterlitz-Thouless (BKT)-type transition. Heat capacity measurements even at zero field manifested an appearance of the additional anomaly at temperatures below the Néel temperature. The temperature dependence of ESR intensity, linewidth and shift of the resonant field imply an extended region of short-range order correlations in the compound studied. The rich variety of the anomalies in magnetic and resonance properties makes this new antimonate a very interesting system to investigate the multiple phase transitions and competing exchange interaction due to the critical role of the layered structure organization accompanied by the frustration effects in triangular antiferromagnets.

Crucial Role of Site Disorder and Frustration in Unusual Magnetic Properties of Quasi-2D Triangular Lattice Antimonate Na4FeSbO6

“…1). Many other aNaFeO 2 superstructures including Li 4 FeSbO 6 [28] are monoclinic (C2/m), although each individual layer is essentially trigonal. Thus the crystal structure of Na 4 FeSbO 6 may well be monoclinic, so we consider two monoclinic structures C2 and C2/m in addition to the P3 1 12 structure (Fig.…”

“…With h = -17 K and T N = 3.6 K, Li 4 FeSbO 6 has f = 4.7, so the spin frustrations arising from the triangular spin lattice are not strong enough to prevent a long-range AFM ordering. Since Na 4 FeSbO 6 [27] is structurally analogous to Li 4 FeSbO 6 [28], one would expect Na 4 FeSbO 6 and Li 4 FeSbO 6 to possess similar magnetic properties. In contrast, our experimental and theoretical investigations show that Na 4 FeSbO 6 has antisite disorders between the Fe 3?…”

“…The present work is concerned with the antisite disorder in the layered oxide Na 4 FeSbO 6 [27]. Na 4 FeSbO 6 [27] is structurally quite similar to the layered oxide Li 4 FeSbO 6 [28], in which the (LiFeSbO 6 ) 3-layers parallel to the ab-plane alternate with layers of Li ? ions along the c-direction.…”

Orbitally induced hierarchy of exchange interactions in the zigzag antiferromagnetic state of honeycomb silver delafossite Ag3Co2SbO6

“…S3). It is worth to mention that the spin-reorientation-type transitions have been reported recently for several related antimonates: for example, Na 3 Co 2 SbO 6 [61], Li 3 Ni 2 SbO 6 [63], Na 3 Ni 2 SbO 6 [76], Li 4 FeSbO 6 [67]. …”

“…The theory for octahedral field predicts that the EPR spectrum from high-spin Co 2+ may be observed mainly at low temperatures because of spin-lattice relaxation time is extremely short for octahedral coordination of Co 2+ , while at high temperature spectra are usually undetectable to its strong broadening. The expected effective gfactor for high-spin Co 2+ is 4.3 in ideal oxygen octahedral environment [67,68] or takes lower value in distorted octahedral coordination. Below certain characteristic temperature T SRO both g-factor and the linewidth increase progressively upon lowering of the temperature and reveal clear anomalies in the vicinity of Néel temperature.…”