Weak ferromagnetism ofCuxFe1+yAsand its evolution with Co doping

Abstract

We have investigated electronic and magnetic properties of iron pnictide Cu x Fe 1+y As, which is isostructural to iron pnictide superconductors LiFeAs and NaFeAs, using polycrystalline and single crystal samples. We found that Cu x Fe 1+y As is characterized by strong electron correlations and shows weak ferromagnetic behavior with the Curie temperature T c ~ 42 K, in contrast with the superconductivity in LiFeAs and NaFeAs. Its electronic transport properties exhibit quasi-two-dimensional characteristics: while the in-plane resistivity follows quadratic temperature dependence for T < 10K, the c-axis resistivity shows nonmetal-to-metal crossover near 20 K. In addition, we have studied Co doping effect on Cu x Fe 1+y As and found that Co doping enhances the ferromagnetism with T c increasing up to 83 K for Cu x Fe 0.5 Co 0.5 As. From these results, we discussed the origin of the ferromagnetism of Cu x Fe 1+y As and its relevance with the magnetism of iron pnictide superconductor parent compounds 2

G -type magnetic order in ferropnictide CuxFe1−yZou1, Lee2, Cao3 et al. 2017Phys. Rev. BSelf Cite2290View full textAdd to dashboardCite

“…One can see a dramatic increase in magnetic moment around 63 K, which suggests the onset of the weak FM state, a feature similar to what was reported previously [38]. The small cusp in the specific heat at 63 K can be associated with the occurrence of this weak ferromagnetism.…”

“…Given that Cu x Fe 1-y As shows quasi-two-dimensional metallic transport properties, it is not surprising to lead to small ordered moments. The in-plane FM component arising from the spin canting in the AFM state revealed in our experiments accounts for the previously reported weak ferromagnetism in Cu x Fe 1-y As [38]. In contrast, for T N2 < T <T N1 , the AFM state should feature a typical G-type order without spin canting (Fig.…”

“…2(a) displays the temperature dependence of the heat capacity of Cu x Fe 1-y As, from which two anomalies can be seen. The first anomaly occurs at T ~ 220 K, which has not been reported in previous studies [33,34,38,39]. The second anomaly, which is much weaker than the one near 220 K, occurs near 63 K. This can be attributed to the presence of the weak ferromagnetism arising from spin canting in the AFM state as discussed below.…”

“…The reported magnetic properties of this material are controversial. CuFeAs was initially Single crystals of CuFeAs were synthesized using self-flux method [38]. The actual composition of the sample used in this study is also nonstoichiometric, i.e.…”

57Fe Mössbauer spectroscopy on iron based pnictides and chalcogenides in applied magnetic fields

“…In the previous paragraph, we discussed O as an example to prove AFM order with small moments. The same experiments we did on CuFeAs, where it is still under debate whether the ground state is ferro‐ or antiferromagnetic . The Mössbauer spectrum shows a sharp onset of broadening at 10 K (Fig.…”