Abstract
The serial system Srn+1FenO2n+1(n=1,2,3…) with the FeO4 square planar motif exhibits abundant phase transitions under pressure. In this work, we investigate the pressure-induced structural, magnetic and transport transitions in Sr2FeO3 from first-principles. Our results show that the system undergoes a structural transition from Immm to Ammm when the volume decreases by 30%, together with a spin-state transition (SST) from high-spin (S = 2) to intermediate-spin (S = 1), an antiferromagnetic-to-ferromagnetic transition and an insulator-to-metal transition (IMT). Besides, the IMT here is a bandwidth controlled transition, but little influenced by the SST.
Highlights
The spin-state transition (SST) in 3d transition metal compounds has been studied extensively.The stabilization of one state over another is mainly from the competition between Hund’s rule coupling and crystal field splitting: the former favors a high spin (HS) and the later favors a low spin (LS).[1]
Our results show that the system will undergo a structural transition from Immm to Ammm when the volume decreases by 30%, together with a SST from HS (S = 2) to intermediate-spin (IS, S = 1), an AF-to-FM transition and an insulator-to-metal transition (IMT)
The infinite FeO2 layer structure in SrFeO2 is cut into two-legged ladders Sr2Fe2O4 and one-dimension chains SrFeO2 in Sr3Fe2O5 and Sr2FeO3 respectively
Summary
The spin-state transition (SST) in 3d transition metal compounds has been studied extensively. FeO4 square planes share their corners to form infinite FeO2 layers in SrFeO2, which undergoes a SST from HS (S = 2) to intermediate-spin (IS, S = 1) state at Pc = 33 GPa.[6] This is accompanied with an insulator-to-metal and an antiferromagnetic(AF)-to-ferromagnetic(FM) transition. The two-legged spin ladder Sr3Fe2O5 (n = 2), in which the infinite FeO2 layers are cut into two-legged ladders (Sr2Fe2O4) by two consecutive rock salt layers (SrO), first exhibits a structural transition from Immm to Ammm at Ps = 30 GPa, exhibits the aforementioned three transitions at Pc = 34 GPa.[7] The mechanism of SST and IMT are studied theoretically, which has been clarified that the SST of SrFeO2 is either induced by the Fe d-O p hybridization in FeO4 plane[6] or the face-to-face FeO4 motif arrangement.[8] Whereas for Sr3Fe2O5, the SST and IMT have a different origin: the HS-IS SST can be triggered solely by the decreasing intralayer Fe-O bondlengths, while the IMT is determined by the reduced interlayer Fe-Fe distance.[9]. The IMT is mainly from the band widening, but little related to the SST
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