Interplay betweenCo 3dandCe 4fmagnetism in CeCoAsO

Abstract

We have investigated the ground-state properties of polycrystalline CeCoAsO by means of magnetization, specific heat, and solid-state NMR. Susceptibility and specific-heat measurements suggest a ferromagnetic order at about, T C = 75 K. No further transitions are found down to 0.5 K. At 6.5 K a complex Schottky type of anomaly shows up in the specific-heat results. The interplay between Ce 4f and Co 3d magnetism being responsible for that anomaly is discussed. Furthermore 75 As-NMR investigations have been performed to probe the magnetism on a microscopic scale. As-NMR spectra are analyzed in terms of first and second-order quadrupolar interaction. The anisotropic shift component K ab and K c could be derived from the 75 As powder spectra. Towards lower temperature a strong shift anisotropy was found. Nonetheless K iso tracks the bulk susceptibility down to T = 50 K very well. Furthermore the presence of weak correlations among the Ce ions in the ferromagnetic state is discussed. The observed increase in C / T towards lower temperatures supports this interpretation.

Tunable interplay between3dand4felectrons in Co-doped iron pnictides

“…According to µ eff = (µ 1/2 , we can estimate the effective moment of Co, which gives µ Co =1.2 µ B , being consistent with that reported in Ref. 26.…”

“…[23][24][25] Moreover, the Co-end compounds, namely ReCoP nO, demonstrate rich magnetic properties attributed to the interactions between the 3d and 4f electrons. For example, CeCoAsO and CeCoPO exhibit an enhanced Sommerfeld coefficient of 200 mJ/mol-K 2 , and their Co-ions undergo a FM transition at T Co C = 75 K. 26,27 LaCoAsO and LaCoPO are itinerant ferromagnets with a Curie temperature of T Co C = 50 K and 60 K, respectively. 28 Complex magnetic properties were observed in SmCoAsO and NdCoAsO, in which the Co-ions first undergo a FM transition and then an AFM transition upon cooling from room temperature, 29,30 followed by an AFM transition of the 4f electrons at T Sm N = 5 K and T Nd N = 3.5 K. 29,30 In GdCoAsO, both Co and Gd are magnetically ordered too, 31 but there is no systematic study so far.…”

CeNiAsO: an antiferromagnetic dense Kondo lattice

“…Previous first principles calculation on LaT AsO [21] suggested that Fe and Co ions show SDW-like and FM instabilities at low temperatures respectively, while Ni ions display nonmagnetic behavior. For CeT AsO, Fe ions in CeFeAsO indeed show SDW-like AFM instability and Co ions in CeCoAsO are FM ordered [14,15], meanwhile neither local magnetic moment nor long range magnetic order of Ni ions is observed in CeNiAsO. However, this does not mean that the Kondo coupling between Ce moment and conduction carriers in the NiAs layer is weaker than that in the FeAs layer.…”

“…By comparison, CeOsPO shows the Ce 3+ AFM order at 4.5 K while CeRuPO is a rare example of the FM Kondo lattice with T C = 15 K [12]. For the case of T = Co, both CeCoPO and CeCoAsO show the FM correlated Co-3d magnetism [13,14,15].…”

Magnetocrystalline anisotropic effect inGdCo1−xFexAsO(x=0,0.05)

“…16,17 On the Co-rich side, the ferromagnetically ordered Co ions have a strong polarization effect on the AFM order of Ce moments. 14,18 On the other hand, in the Gd(Fe,Co)AsO series, which correspond to the case of a large 4f -magnetic moment, Fe/Co substitution also leads to a superconducting dome near the 3d-electron magnetic instability. 14 On the Co-rich side, in contrast to the Ce-case, the large moment of Gd ions is robust against the FM order of Co moments, and maintains its AFM order with a nearly unchanged Néel temperature over the entire doping range.…”