Fe-Site Substitution Effect on the Structural and Magnetic Properties in SrFeO₂

Abstract

We investigated the Fe-site substitution effect on the structural and magnetic properties of the infinite layer iron oxide Sr(Fe(1-x)M(x))O(2) (M = Co, Mn) using synchrotron X-ray diffraction, neutron diffraction, and (57)Fe Mössbauer spectroscopy. Both systems have a similar solubility limit of x ≈ 0.3, retaining the ideal infinite layer structure with a space group of P4/mmm. For the Fe-Co system, both in-plane and out-of-plane axes decrease linearly and only slightly with x, reflecting the ionic radius difference between Fe(2+) and Co(2+). For the Fe-Mn system the lattice evolution also follows Vegard's law but is anisotropic: the in-plane axis increases, while the out-of-plane decreases prominently. The magnetic properties are little influenced by Co substitution. On the contrary, Mn substitution drastically destabilizes the G-type magnetic order, featured by a significant reduction and a large distribution of the hyperfine field in the Mössbauer spectra, which suggests the presence of magnetic frustration induced presumably by a ferromagnetic out-of-plane Mn-Fe interaction.

Electronic structure and magnetic properties of SrFe1−Mn O2: A theoretical investigation

“…When 12.5% Fe is substituted by Mn, our calculations show that the (πππ)-type AF1 magnetic ordering still remains to be the most stable state, which is in agreement with the experimental results [6]. It means that a small quantity of doping is not able to change the magnetic structure.…”

“…We used a larger U in our first-principles calculation than theirs, and hence, smaller exchange parameters are obtained according to J∼t 2 /U. We note that if we rescale the transition temperature for x¼0 according to the experimental data, the transition temperatures for x ¼0.1, 0.2, and 0.3 would be 390, 320, and 270 K, respectively, in agreement with experiment results [6,7]. The specific heat curve peaks get more round with increasing x as shown in Fig.…”

“…Because the generalized gradient approximation (GGA) [20] usually fails to predict the ground state of transition-metal oxides [21], generalized gradient approximation plus on site repulsion U (GGA þ U) [22] (in combination with ultrasoft pseudopotentials [23]) are used in our calculations. The crystal structure of SrFe 1 À x Mn x O 2 belongs to the space group P4/mmm within the solubility limit of x E0.3 [6]. A super-cell with 32 atoms is used in our calculations for the total energy and the density of states (DOS) for different dopant concentrations and atomic configurations.…”

“…The magnetic phase transition in SrFeO 2 can also be induced through the Fe-side substitution by other 3d transition-metal elements. It was found that the Fe-side substitution by Mn (or Co) can keep the crystal structure unchanged up to the solubility limit of x E0.3 [6]. For SrFe 1 À x Co x O 2 , the reduction of T N relative to SrFeO 2 is no more than 50 K. However, the Néel temperature of SrFe 1 À x Mn x O 2 decreases substantially with increasing x.…”

First-principles study of the electronic structure and magnetism of SrFe0.5Ru0.5O2

“…The magnetic phase transition in SrFeO 2 can also be induced through the Fe-site substitution by other 3d-transition elements. For example, Fe-site substitution by Mn can keep the compound structure unchanged up to 30% solvability [5], but a mixed magnetic (πππ) and (ππ0) ordering was detected by neutron diffraction measurements. Recently, Romero et al synthesized Ru substituted compound SrFe 0.5 Ru 0.5 O 2 [6], which is isostructural with SrFeO 2 .…”