Fe_xPb_4−xSb₄Se₁₀: A New Class of Ferromagnetic Semiconductors with Quasi 1D {Fe₂Se₁₀} Ladders

Abstract

A new family of quasi-one-dimensional ferromagnetic selenides with general formula Fe(x)Pb(4-x)Sb(4)Se(10) (0 < or = x < or = 2) was generated by isoelectronic substitution in octahedral positions of Pb atoms by Fe within the structure of Pb(4)Sb(4)Se(10). Two members of this family with x = 0.75 and x = 1 were synthesized as a single phase through direct combination of the elements at 823 K. Single crystal X-ray diffraction revealed that Fe(0.75)Pb(3.25)Sb(4)Se(10) crystallizes with the orthorhombic space group Pnma, whereas Fe(0.96)Pb(3.04)Sb(4)Se(10) adopts the lower symmetry monoclinic subgroup P2(1)/m (#11). Both compounds are isomorphous with Pb(4)Sb(4)Se(10), and their crystal structures consist of corrugated layers of edge-sharing bicapped trigonal prisms and octahedra around Pb atoms. Adjacent layers are interconnected by NaCl-type {SbSe} ribbons. The voids left by this arrangement are filled by the novel one-dimensional {Fe(2)Se(10)} double chains (ladder) of edge-sharing octahedra running along [010]. Temperature dependent magnetic susceptibility as well as field dependent magnetization isotherms showed that both Fe(0.75)Pb(3.25)Sb(4)Se(10) and FePb(3)Sb(4)Se(10) are ferromagnetic below 300 K and exhibit superparamagnetism at higher temperatures. A dramatic reduction in the magnetic moment per Fe(2+), approximately 0.40 micro(B), was observed in Fe(0.75)Pb(3.25)Sb(4)Se(10) and FePb(3)Sb(4)Se(10) suggesting that the Fe(x)Pb(4-x)Sb(4)Se(10) (0 < or = x < or = 2) phases are not ordinary ferromagnets where all the magnetic spins are parallel at low temperatures. Analysis of the magnetic coupling of spins located on adjacent Fe atoms (within a localized Fe(2+) moment picture) using Goodenough-Kanamori rules suggested that the magnetism within the ladder and ladder-single chain systems in Fe(x)Pb(4-x)Sb(4)Se(10) phases is controlled by competing interactions.

Crystal Structure of FePb4Sb6Se14 and its Structural Relationship with FePb3Sb4Se10

“…The unusually long Sb–Se bond, originating from the stereochemical activity of the antimony lone‐pair, results in the bond valence sum (BVS) calculations for antimony atoms deviating from the expected theoretical value of 3.0 (Table 2). The lone‐pair electron clouds on neighboring antimony atoms, form a micelle similar to the one observed in the structure of FePb 4 Sb 6 S 14 26 and FePb 3 Sb 4 Se 10 ,28 within the center of the {SbSe} ∞ ribbon in the structure of FePb 4 Sb 6 Se 14 (Figure 1).…”

“…The crystal structure of FePb 4 Sb 6 Se 14 is closely related to that of FePb 3 Sb 4 Se 10 , the member with x = 1 of the newly discovered series of ferromagnetic semiconductors with general formula (Fe x Pb 2– x )Pb 2 Sb 4 Se 10 (0 ≤ x ≤ 2) 28. As highlighted in Figure 3, both crystal structures are formed by similar building units (a corrugated layer of lead atoms, a 1D‐{SbSe} ribbon of antimony atoms, and a 1D chain of iron atoms).…”

“…Several such compounds, for example, MnSb 2 (S, Se) 4 ,21,22 FePb 3 Sn 4 Sb 2 S 14 ,23 and (Mn, Fe)Pb 4 Sb 6 S 14 ,24–26 are one‐dimensional (1D) anti‐ferromagnetic semiconductors containing quasi‐isolated magnetic single straight chains of edge‐sharing MQ 6 (M = Mn, Fe; Q = S, Se) octahedra separated by the main‐group metal chalcogenide semiconducting framework. Recently, we observed the coexistence of a robust ferromagnetism and semiconductivity above room temperature in the FeSb 2 Se 4 and Fe x Pb 4– x Sb 4 Se 10 compositions 27,28. The coexistence of high Curie temperatures ferromagnetism and semiconductivity in these compounds is desirable for the development of promising spintronic materials.…”

“…Therefore, a broad range of multifunctional applications are accessible via crystal engineering of the structure of main‐group metal chalcogenides. Here, we report on the crystal structure of FePb 4 Sb 6 Se 14 , the selenium analog of the mineral Jamesonite (FePb 4 Sb 6 S 14 , band gap = 0.48 eV)24 and discuss its structural relationship with FePb 3 Sb 4 Se 10 28…”

Studies on structural and magnetic properties of hydrochloride crystals based on 2-(imidazo[1,2–a]pyridin-2-yl)-2-oxoacetic acid radical

“…3. The magnetization curve indicates an S-shaped curvature, and the magnetic hysteresis was observed with remanant magnetization, M r , of 0.066 emu mol À 1 and coercive field (H c ) of 265 Oe, indicating its 'soft' magnet behavior [18]. Because radical molecules in 2 exist as diamagnetic dimers, crystal 2 exhibits very low magnetic susceptibility at room temperature (only 0.009 emu K mol À 1 at 300 K), as shown in Fig.…”