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Unconventional magnetism in the spin-orbit-driven Mott insulators Ba3MIr2O9 (M=Sc,Y)

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Title Unconventional magnetism in the spin-orbit-driven Mott insulators Ba3MIr2O9 (M=Sc,Y)
 
Creator DEY, T
KUMAR, R
MAHAJAN, AV
KAUSHIK, SD
SIRUGURI, V
 
Subject SINGLE-CRYSTAL
NMR
SR2IRO4
GAP
 
Description We have carried out detailed bulk and local probe studies on the hexagonal oxides Ba3MIr2O9 (M= Sc,Y), where Ir is expected to have a fractional oxidation state of + 4.5. In the structure, Ir-Ir dimers are arranged in an edge-shared triangular network parallel to the ab plane. Whereas only weak anomalies are evident in the susceptibility data, clearer anomalies are present in the heat capacity data-around 10 K for Ba3ScIr2O9 and at 4 K for Ba3YIr2O9. Our Sc-45 nuclear magnetic resonance (NMR) line shape (first-order quadrupole split) is symmetric at room temperature but becomes progressively asymmetric with decreasing temperatures indicating the presence of developing inequivalent Sc environments. This is suggestive of distortions in the structure which could arise from progressive tilt/rotation of the IrO6 octahedra with a decrease in temperature T. The 45Sc NMR spectral weight shifts near the reference frequency with decreasing T indicating the development of magnetic singlet regions. Around 10 K, a significant change in the spectrum takes place with a large intensity appearing near the reference frequency but with the spectrum remaining multipeak. It appears from our Sc-45 NMR data that in Ba3ScIr2O9 significant disorder is still present below 10 K. In the case of Ba3YIr2O9, the Y-89 NMR spectral lines are asymmetric at high temperatures but become nearly symmetric (single magnetic environment) below T similar to 70 K. Our Y-89 spectra and T-1 measurements confirm the onset of long-range ordering from a bulk of the sample at 4 K in this compound. Our results suggest that Ba3YIr2O9 might be structurally distorted at room temperature (via, for example, tilt/rotations of the IrO6 octahedra) but becomes progressively a regular triangular lattice with decreasing T. The effective magnetic moments and magnetic entropy changes are strongly reduced in Ba3YIr2O9 as compared to those expected for a S = 1/2 system. Similar effects have been found in other iridates which naturally have strong spin-orbit coupling.
 
Publisher AMER PHYSICAL SOC
 
Date 2014-12-28T13:12:47Z
2014-12-28T13:12:47Z
2014
 
Type Article
 
Identifier PHYSICAL REVIEW B, 89(20)
1098-0121
1550-235X
http://dx.doi.org/10.1103/PhysRevB.89.205101
http://dspace.library.iitb.ac.in/jspui/handle/100/16687
 
Language English