Coexistence of high electrical conductivity and weak ferromagnetism in Cr doped Y2Ir2O7 pyrochlore iridates

Abstract

We report the structural, magnetic and electrical transport properties of Y2Ir2−xCrxO7 pyrochlore iridates. The chemical doping leads to order of magnitude enhancement of electrical conductivity. The introduction of Cr 3+ at Ir 4+ -site tends to distort the Ir − O6 octahedra and suppresses antiferromagnetic correlation. The X-ray photoemission spectroscopy measurements suggest the coexistence of Ir 4+ and Ir 5+ valence states in the Y2Ir2−xCrxO7 compounds. The concentration of Ir 5+ is enhanced with Cr doping, leading to weak ferromagnetism and enhanced electrical conductivity. A cluster-glass like transition is also observed at low temperature with Cr doping, possibly due to competing ferromagnetic and antiferromagnetic interaction. arXiv:1904.05541v1 [cond-mat.mtrl-sci]

Influence of electronic structure parameters on the electrical transport and magnetic properties of Y2−xBixIr2O7 pyrochlore iridates

“…For Ir 4+ , 4f 7/2 and 4f 5/2 electronic states arise at binding energy around 62eV and 65eV due to spin-orbit coupling, respectively, which are represented by blue solid line and blue dashed line in Fig 10a. Similarly, higher oxidation state Ir 5+ centered at 63.7eV and 67eV shown by green solid line and green dashed line, respectively in Fig 10a for 4f 7/2 and 4f 5/2 . Fitted result show very small contribution from the Ir 5+ oxidation state along with major contribution from the Ir 4+ charge state for x = 0.0 sample, consistent with previous reports 24,25,30 . For Bi doped compounds, the contribution from Ir 5+ is minimally increased.…”

“…Interestingly, susceptibility enhances very sharply below T ∼ 25K, possibly due to emergence of very weak ferromagnetic components. This behaviour might be attributed to spin-glass like transition 25,31 . As shown in the Fig.…”

Non-Fermi liquid regime in metallic pyrochlore iridates: Quantum Griffiths singularities

“…Bulk polycrystalline samples of Pr 2 Ir 2−x Cr x O 7 (PICO), where x = 0, 0.05, 0.1, 0.2, 0.3, were grown by conventional solid state reaction route [21][22][23][24] using powders of Pr 2 O 3 , IrO 2 and Cr 2 O 3 , mixed in their stoichiometric ratios. The samples were characterized by powder x-ray diffraction (XRD) measurement using PANalytical XPertPro diffractometer at room temperature.…”

“…1d. The value of X for an ideal IrO 6 octahedra in Pyrochlore structure is 0.3125, where the Ir 4+ ions are placed under an ideal cubic symmetry 3,21 . The estimated value for parent sample x = 0.0 turns out to be 0.329, which is close to the ideal value.…”

“…After 3000 sec, the percentage change in M (t)/M (0) is 0.4% for x = 0 while the same for x = 0.3 is 3.2% for = 0.3. Long time magnetic relaxation due to spin glass or Griffiths phase is generally described by a stretched exponential function 21 , where τ is characteristic relaxation time and β is the stretching exponent which determines the shape of magnetic relaxation. We observe a pure exponential time relaxation at shorter time scale with the value of β being close to unity for x = 0 and 0.3, as demonstrated in the semi-log plot (Fig.…”