Abstract
The electronic ground state of iron-based materials is unusually sensitive to electronic correlations. Among others, its delicate balance is profoundly affected by the insertion of magnetic impurities in the FeAs layers. Here, we address the effects of Fe-to-Mn substitution in the non-superconducting Sm-1111 pnictide parent compound via a comparative study of SmFe_{1-x}Mn_{x}AsO samples with x(text{Mn})= 0.05 and 0.10. Magnetization, Hall effect, and muon-spin spectroscopy data provide a coherent picture, indicating a weakening of the commensurate Fe spin-density-wave (SDW) order, as shown by the lowering of the SDW transition temperature T_text{SDW} with increasing Mn content, and the unexpected appearance of another magnetic order, occurring at T^{*} approx 10 and 20 K for x=0.05 and 0.10, respectively. We attribute the new magnetic transition at T^{*}, occurring well inside the SDW phase, to a reorganization of the Fermi surface due to Fe-to-Mn substitutions. These give rise to enhanced magnetic fluctuations along the incommensurate wavevector varvec{Q}_2 =(pi pm delta ,pi pm delta ), further increased by the RKKY interactions among Mn impurities.
Highlights
Electronic correlations play a crucial role in the way pnictide compounds switch their originally magnetic ground state to a superconducting one and vice versa
Apart from the details, here related to the multiband nature of the 1111 pnictide family, the abrupt anomalies at T∗ = 10 K and 20 K strongly suggest a reorganization of the electronic bands, an effect that scales with Mn content
Our data clearly show that even a tiny partial substitution of Mn at the iron sites strongly affects the electronic properties of the SmFeAsO parent compound: (1) it progressively suppresses the SDW transition temperature TSDW ; (2) it induces a new low-temperature magnetic transition at T∗ < TSDW, clearly manifest in both the transport (Hall effect) and the magnetic properties
Summary
Electronic correlations play a crucial role in the way pnictide compounds switch their originally magnetic ground state to a superconducting one and vice versa. Strong electronic correlations enhance the magnetic coupling between the diluted Mn ions through the Ruderman–Kittel–Kasuya–Yosida (RKKY) mechanism, an indirect exchange interaction able to magnetically correlate impurity spins separated by several unit cells This interaction reinforces the tendency towards an antiferromagnetic order in LaFe1−xMnxAsO1−yFy3. Despite a higher chemical pressure with respect to LaFe1−xMnxAsO, expected to weaken the electronic correlations, in the Sm-1111 case, they are still sufficiently strong to sustain a Mn-Mn coupling via RKKY interactions. Such magnetic coupling is able to pin the electronic charges locally, resulting in a full reorganization of the Fermi surface and the onset of an incommensurate antiferromagnetic (AF) order at low temperature, well inside the existing SDW phase
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