Colossal enhancement of electrical conductivity in Y₂Ir₂O₇nanoparticles

Abstract

Abstract.We present a comparative study of the magnetic and electrical properties of polycrystalline and nanocrystalline Y 2 Ir 2 O 7 , the latter prepared using a new chemical route. We find that reduction in particle size leads to enhanced ferromagnetism and orders of magnitude enhancement of electrical conductivity in the nanocrystalline sample. Based on X-ray photoelectron spectroscopy and X-ray absorption near edge structure spectroscopy results, the phenomenon is attributed to the increased fraction of Ir 5+ and the resulting increase in double exchange interaction along with the weakening of spin-orbit coupling strength in the nanocrystalline sample compared to the bulk.

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.…”

“…Figure 1 shows powder X-ray diffraction (XRD) pattern for Y 2−x Bi x Ir 2 O 7 series with x = 0.0, 0.1, 0.2 and 0.3. The XRD spectra with diffraction peaks for the undoped compound (x = 0.0) consistent with the reported study 24 . With substitution of Bi at Y -site, major change in XRD peak position is not observed.…”

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

“…The accuracy of all refined values of XRD data is ∼ ±0.002 0 . Analysis of XRD spectra indicate that all the samples crystallize in the F-centered cubic unit cell with F d3m symmetry, which is consistent with previous reports 28,29 . XRD pattern shows no major changes in the peak positions with doping.…”

“…On the other hand, muon spin rotation and relaxation experiment analysed with ab initio modeling 27 suggest a long range magnetic transition with all-in/all-out AFM ground state at low temperatures. There are few earlier reports which also suggest existence of weak ferromagnetic component over the AFM background in Y 2 Ir 2 O 7 [28][29][30] . Since, pyrochlore iridates are geometrically frustrated, therefore the low temperature magnetic state of Y 2 Ir 2 O 7 could show glass-like behaviour 3,7,31,32 , similar to other Y-based pyrochlores such as R 2 Os 2 O 7 (R = Y and Ho) 33 In the present work, we have studied the effect of magnetic Cr ion introduction at magnetic Ir-site in Y 2 Ir 2−x Cr x O 7 .…”

Suppression of long range magnetic ordering and electrical conduction in Y1.7Bi0.3Ir2<

“…3d) . in S2 and several other pyrochlore iridate systems [9,10,11,12,13,14,15,16]. However, strikingly, the bifurcation between χ ZF C and χ F C branches commonly observed for S2 [inset of Fig.…”