The role of magnetic excitations in magnetoresistance and Hall effect of slightly TM-substituted BaFe2As2 compounds (TM = Mn, Cu, Ni)

Abstract

We report on electrical resistivity, magnetoresistance (MR) and Hall effect measurements in four non-superconducting BaFe2−xTMxAs2 (TM = Mn, Cu and Ni) single crystals with small values of the chemical substitution x. The spin density wave (SDW) ordering that occurs in these systems at temperatures T ∼ (120 -140) K, in close vicinity to a tetragonal/orthorhombic transition, produces significant modifications in their magneto-transport properties. While in the magnetically ordered phase the MR is positive and its magnitude increases with decreasing temperatures, in the paramagnetic regime the MR becomes vanishingly small. Above the spin density wave transition temperature (TSDW) the Hall coefficient RH is negative, small and weakly temperature dependent, but a remarkable change of slope occurs in the RH versus T curves at T = TSDW. The Hall coefficient amplitude, while remaining negative, increases steadily and significantly as the temperature is decreased below TSDW and down to T = 20 K. The qualitative behavior of both MR and Hall coefficient is weakly dependent on the chemical substitution in the studied limit. The experiments provide strong evidence that scattering of charge carriers by magnetic excitations has to be taken into account to explain the behavior of the resistivity, magnetoresistance and Hall effect in the ordered phase of the studied compounds. Effects of multiple band conduction also must be considered for a complete interpretation of the results.

Magnetotransport properties in the magnetic phase of BaFe2−xTxAs2(T=Co,Ni

“…Lifshitz transitions and exotic temperature-dependent Fermi surfaces explain only partially the behavior of the MR and Hall coefficient. Our previous results in slightly doped and nonsuperconducting samples[7] as well as the results of this paper in samples having a superconducting ground state while preserving an intermediate magnetic phase reveal that, once a magnetic transition occurs, large changes in the absolute values and temperature dependence of MR and the Hall coefficient are observed in the region T T SDW , independently of the T substitution or of how low T SDW is.…”

“…The importance of the scattering by magnetic fluctuations to the transport properties of Fe-based 122 pnictides, superconducting or not, has been pointed out in previous works [7,41,42]. For example, the anisotropic resistance in the nematic phase has been described with an Ising-nematic model where the anisotropy is the product of the interference between scattering by impurities and by critical spin fluctuations [41].…”

“…One then observes that tan H (T ) evolves from a linear function of the temperature in the slightly substituted, and nonsuperconducting, samples [7] to an approximately quadratic temperature behavior in samples with higher T content, for which a superconducting ground state is stabilized. It is also shown in the results of Fig.…”

“…In the parent compound of the 122 family, BaFe 2 As 2 , both the transversal magnetoresistance (MR in the geometry B c axis; B ⊥ I ) and the Hall coefficient, R H , exhibit unusual magnetic-field and temperature dependencies in the region T < T SDW [3][4][5][6][7]. In particular, the absolute values of the MR and R H sharply increase when the temperature decreases below T SDW .…”

“…NM denotes "Not measured." quasiparticle scattering spectrum, some authors proposed that carrier scattering by magnetic excitations plays an additional, relevant mechanism for completely describing the magnetotransport properties of the Fe-based pnictides, including the T -substituted systems [7,17].…”