Intralayer doping effects on the high-energy magnetic correlations in NaFeAs

Abstract

We have used Resonant Inelastic X-ray Scattering (RIXS) and dynamical susceptibility calculations to study the magnetic excitations in NaFe 1−x Co x As (x = 0, 0.03 and 0.08). Despite a relatively low ordered magnetic moment, collective magnetic modes are observed in parent compounds (x = 0) and persist in optimally (x = 0.03) and overdoped (x = 0.08) samples. Their magnetic bandwidths are unaffected by doping within the range investigated. High energy magnetic excitations in iron pnictides are robust against doping, and present irrespectively of the ordered magnetic moment. Nevertheless, Co doping slightly reduces the overall magnetic spectral weight, differently from previous studies on hole-doped BaFe 2 As 2 , where it was observed constant.Finally, we demonstrate that the doping evolution of magnetic modes is different for the dopants being inside or outside the Fe-As layer.

Presence of magnetic excitations in SmFeAsO

“…such as neutron scattering [10][11][12][13][14] and / or X-Ray Scattering [15,16]. Neutron scattering experiments confirmed the presence of sizable magnetic moments in Fe pnictides (on the order of ≈ 1 µ B ) [2,3,10] with few exceptions, such as NaFeAs that shows lower ordered magnetic moment [2,3].…”

“…Moreover, the growth of suitable crystals for INS is challenging and this complicates the measurements of high energy spin excitations (> 90 meV), where INS would provide plenty of information [10][11][12]24]. These drawbacks can be minimized by employing RIXS, which has been previously employed in the detection of high energy spin excitations in NaFeAs and BaFe 2 As 2 Fe pnictides [15,16]. Moreover, thanks to the high refocusing (beam spot of 5x20 µm 2 VxH at the ADRESS beamline of the Swiss Light Source) and flux obtainable at the sample for modern beamlines [25], the amount of sample required for these investigations is on the order of tens of milligrams and crystals of the size 150x200 micrometers can now be successfully studied, even measuring down to a single layer of material [26].…”

“…The main line in this spectrum resembles emission from metallic systems with a broad asymmetric peak displaying a maximum at around -2 eV in energy loss (hν out -hν in ) [15,16,29,31], arising from resonant emission of itinerant electrons. In contrast to doped 1111 [32], but in agreement with other Fe pnictides, the emission line is not showing any sharp features ascribable to dd-excitations [15,16,29,30]. This confirms the moderate electronic correlations of Fe pnictides contrasting with Fe chalcogenides where dd-excitations have been observed employing hard X-ray RIXS [33].…”

“…The energy range and the dispersive nature of this mode resemble the behavior of spin excitations detected by RIXS in BaFe 2 As 2 [15] and NaFeAs (measurements shown in Supplemental Material). We fit the background, the elastic and the magnetic line in agreement to [15,16,31] and plot the results in Fig. 2.…”

“…The spectrum is composed of a broad peak centered at 707 eV, typical of metallic systems containing Fe [15,16,29,30]. The incident energy for RIXS was tuned at the main Fe-L 3 peak.…”