Interplay of Fe and Nd magnetism in NdFeAsO single crystals

Abstract

The structural and magnetic phase transitions have been studied on NdFeAsO single crystals by neutron and x-ray diffraction complemented by resistivity and specific heat measurements. Two low-temperature phase transitions have been observed in addition to the tetragonal-to-orthorhombic transition at TS ∼ 142 K and the onset of antiferromagnetic (AFM) Fe order below TN ∼ 137 K. The Fe moments order AFM in the well-known stripe-like structure in the (ab) plane, but change from AFM to ferromagnetic (FM) arrangement along the c direction below T * ∼ 15 K accompanied by the onset of Nd AFM order below T Nd ∼ 6 K with this same AFM configuration. The iron magnetic order-order transition in NdFeAsO accentuates the Nd-Fe interaction and the delicate balance of c-axis exchange couplings that results in AFM in LaFeAsO and FM in CeFeAsO and PrFeAsO.

Structural trends from a consistent set of single-crystal data ofRFeAsO(R=La, Ce, Pr, Nd, Sm, Gd, and Tb)

“…Below T = 75 K, ρ(T ) increases again, showing similarities to LaFeAsO 2 , followed by a decrease at T < 18 K. The decrease of ρ(T ) changes slope towards lower temperature with a linear temperature dependece at T < 6 K. The onset of the anomaly at T ≈ 20 K is also observable in polycrystalline material where no data is reported for T ≤ 19 K 24 . A similar behavior was published for NdFeAsO, where the change of the magnetic structure of Fe at T = 15 K results in a significant decrease in the electrical resistivity of single-crystalline material with the current in the abplane 25 . The TbFeAsO single-crystal measured (Fig.…”

Magnetic structures and interplay between rare-earth Ce and Fe magnetism in single-crystal CeFeAsO

“…5,6 Therefore understanding the magnetism in the iron-based parent compounds can lead to insight about the mechanism that induces superconductivity by doping or pressure. 7,8 CeFeAsO is a typical example of rare-earth-containing RFeAsO, with a tetragonal-to-orthorhombic structural transition upon cooling at T S ≈ 150 K, which is followed by the onset of stripelike Fe AFM order below T N ≈ 140 K. 9,10 Long-range AFM ordering of Ce below T Ce ≈ 4 K was first reported in powder neutron diffraction studies proposing a Ce magnetic structure that required further confirmation. 10 This study also suggested that Ce-Fe coupling is relatively strong as it influences the magnetic Fe peaks above T Ce up to ≈20 K. Furthermore, in support of strong Fe-Ce coupling, μSR measurements 11 on polycrystalline CeFeAsO show a considerable 3d-4f hybridization that leads to a considerable staggered Ce magnetization up to almost 120 K, far above T Ce .…”

Temperature dependence of resistivity of RFeAsO compounds

“…Specific heat data for CeFeAsO suggest that the onsets of SPT appear to be at the same temperature for both the single crystalline as well as poly crystalline sample; although the transition appears to be broader for the latter [13,14]. For polycrystalline PrFeAsO (T S , T N ) have been reported to be (153K, 127 K) [15], whereas the same is (142 K, 137 K) for single crystal of NdFeAsO [16]. For SmFeAsO (T S , T N ) is (175 K, 140 K) [17].…”

“…Subsequently, superconductivity has been reported in other RFeAs(O 1-x F x ) compounds with R = Ce, Pr, Nd, Sm, etc., and the reported values of T c are 41 K in CeFeAsO 0.84 F 0. 16 , 52 K in PrFeAsO 0.89 F 0.11 , 54.3 K in NdFeAsO 1-y , 55 K in SmFeAsO 0.9 F 0.1 , and 54 K in GdFeAsO 1-y [4]. By now the iron-based superconductors have been extended to a much larger group containing variety of materials, mainly, four prototypical families 1111, 122, 111, and 11 types, and further variations such as 42622-type iron pnictides and 122-type iron chalcogenides [4].…”