7 research outputs found
Ab initio modeling and experimental investigation of FeP by DFT and spin spectroscopies
FeP alloys have been identified as promising candidates for magnetic
refrigeration at room-temperature and for custom magnetostatic applications.
The intent of this study is to accurately characterize the magnetic ground
state of the parent compound, FeP, with two spectroscopic techniques,
SR and NMR, in order to provide solid bases for further experimental
analysis of FeP-type transition metal based alloys. We perform zero applied
field measurements using both techniques below the ferromagnetic transition
. The experimental results are reproduced and interpreted
using first principles simulations validating this approach for quantitative
estimates in alloys of interest for technological applications.Comment: 10 pages, 2 figure
Disentangling superconducting and magnetic orders in NaFe_1-xNi_xAs using muon spin rotation
Muon spin rotation and relaxation studies have been performed on a "111"
family of iron-based superconductors NaFe_1-xNi_xAs. Static magnetic order was
characterized by obtaining the temperature and doping dependences of the local
ordered magnetic moment size and the volume fraction of the magnetically
ordered regions. For x = 0 and 0.4 %, a transition to a nearly-homogeneous long
range magnetically ordered state is observed, while for higher x than 0.4 %
magnetic order becomes more disordered and is completely suppressed for x = 1.5
%. The magnetic volume fraction continuously decreases with increasing x. The
combination of magnetic and superconducting volumes implies that a
spatially-overlapping coexistence of magnetism and superconductivity spans a
large region of the T-x phase diagram for NaFe_1-xNi_xAs . A strong reduction
of both the ordered moment size and the volume fraction is observed below the
superconducting T_C for x = 0.6, 1.0, and 1.3 %, in contrast to other iron
pnictides in which one of these two parameters exhibits a reduction below TC,
but not both. The suppression of magnetic order is further enhanced with
increased Ni doping, leading to a reentrant non-magnetic state below T_C for x
= 1.3 %. The reentrant behavior indicates an interplay between
antiferromagnetism and superconductivity involving competition for the same
electrons. These observations are consistent with the sign-changing s-wave
superconducting state, which is expected to appear on the verge of microscopic
coexistence and phase separation with magnetism. We also present a universal
linear relationship between the local ordered moment size and the
antiferromagnetic ordering temperature TN across a variety of iron-based
superconductors. We argue that this linear relationship is consistent with an
itinerant-electron approach, in which Fermi surface nesting drives
antiferromagnetic ordering.Comment: 20 pages, 14 figures, Correspondence should be addressed to Prof.
Yasutomo Uemura: [email protected]
Ab initio modeling and experimental investigation of Fe2 P by DFT and spin spectroscopies
Fe2P alloys have been identified as promising candidates for magnetic refrigeration at room-temperature and for custom magnetostatic applications. The intent of this study is to accurately characterize the magnetic ground state of the parent compound, Fe2P, with two spectroscopic techniques, μSR and NMR, in order to provide solid bases for further experimental analysis of Fe2P-type transition metal based alloys. We perform zero applied field measurements using both techniques below the ferromagnetic transition TC=220 K. The experimental results are reproduced and interpreted using first principles simulations, validating this approach for quantitative estimates in alloys of interest for technological applications.</p
Mn-induced Fermi-surface reconstruction in the SmFeAsO parent compound
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 SmFe1-xMnxAsO samples with x(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 TSDW with increasing Mn content, and the unexpected appearance of another magnetic order, occurring at T∗≈ 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 Q2= (π± δ, π± δ) , further increased by the RKKY interactions among Mn impurities.ISSN:2045-232
A Cost-Effective Semi-Ab Initio Approach to Model Relaxation in Rare-Earth Single-Molecule Magnets
We discuss a cost-effective approach to understand magnetic relaxation in the new generation of rare-earth single-molecule magnets. It combines ab initio calculations of the crystal field parameters, of the magneto-elastic coupling with local modes, and of the phonon density of states with fitting of only three microscopic parameters. Although much less demanding than a fully ab initio approach, the method gives important physical insights into the origin of the observed relaxation. By applying it to high-anisotropy compounds with very different relaxation, we demonstrate the power of the approach and pinpoint ingredients for improving the performance of single-molecule magnets