Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridateY2Ir2O7

Abstract

Pyrochlore iridates have recently attracted growing interest in condensed matter physics because of their potential for realizing new topological states. In order to achieve such quantum states, it is essential to understand the magnetic properties of these compounds, as their electronic structures are strongly coupled with their magnetic ground states. In this work, we report a systematic study of the magnetic properties of pyrochlore Y 2 Ir 2 O 7 and its hole-doped compounds by performing magnetic, electron spin resonance (ESR), electrical transport and x-ray photoelectron spectroscopy (XPS) measurements. We demonstrate the existence of weak ferromagnetism on top of a large antiferromagnetic background in the undoped compound. Hole-doping by calcium was found to enhance both the ferromagnetism and the electrical conductivity. The XPS characterization shows the coexistence of Ir 4+ and Ir 5+ in the undoped compound, and the amount of Ir 5+ increases with Ca-doping, which highlights the possible origins of the weak ferromagnetism associated with the formation of Ir 5+ . We also observe a vertical shift in the M -H curves after field cooling, which may arise from a strong coupling between the ferromagnetic phase and the antiferromagnetic background.

Nonequilibrium low temperature phase in pyrochlore iridate Y2Ir2O7: Possibility of glass-like dynamics

“…The moment at 70 kOe is found to be 0.095 µ B /f.u which is much lower than the expected spin-only value (gSµ B ) i.e., 1 µ B /f.u for S = 1/2. This low value of magnetization is consistent with other studies 15,21 . A close observation, however, shows a very small hysteresis in M (H) plot with coercive field H c ∼ 100 Oe and remanent magnetization M r ∼ 4.7 × 10 −4 µ B /f.u.…”

“…2. This similar absence of peak has been observed in other studies as well 15,18,21,25 . This qualitatively suggests magnetic frustration is quite significant in this material which perhaps prevent the long-range type magnetic ordering.…”

“…Magnetically, the Y 2 O 3 is diamagnetic and IrO 2 is paramagnetic therefore, these residual impurities are expected to influence the magnetic properties of desired material minimally. Note, that similar impurity phases have also been observed in previous studies 15,17,21 . In general, pyrochlore materials adopt cubic crystallographic phase with Fd3m symmetry 1 .…”

“…Now we look at the electronic transport behavior in this material. An insulating behavior is evident for Y 2 Ir 2 O 7 in previous studies, however, the resistivity value at low temperature has shown wide variation 16,17,21,26 . Fig.…”

“…The onset of this irreversibility between ZFC and FC magnetization is at temperature T irr ∼ 160 K. Some disagreement has earlier been observed about the value of T irr . While the majority of studies 15,18,21,25 have shown the T irr in the range of 150 -160 K accompanied by a feeble kink in M ZF C around T irr , the another study by Disseler et al 17 shows a higher T irr (190 K) and cusp in M ZF C at T irr . Our observed T irr ∼ 160 K agrees well with the majority of studies.…”