Magnetic properties near the quantum critical point in the pyrochlore iridates (Eu_1-xLa_x)₂Ir₂O₇

Pyrochlore iridates, R₂Ir₂O₇ (R = rare-earth and Y), have been extensively studied over the past decade. A wealth of emergent properties including metal insulator transitions (MITs) and non-trivial topological phases arise due to the combination of spin orbit coupling, geometric frustration and strong electron correlation. The ground state is highly sensitive to the ionic size of R, and evolves from an insulating All-In All-Out (AIAO) antiferromagnetic (AFM) ground state for smaller rare-earth ions (R = Gd, Tb, Dy, Ho, Er, Yb, Y), to a non-magnetic metallic state for large R = Pr. The intermediate members with R = Nd, Sm and Eu, however, show a sharp MIT concurrent with AIAO type AFM long-range ordering. This quantum critical point is attributed to the change of the iridium electronic structure with chemical pressure, although direct experimental evidence remains elusive. Previous divalent (Ca) and trivalent (Bi) cation doping studies create either Ir⁴⁺-Ir⁵⁺ charge disproportionation or large Bi 6p-Ir 5d hybridization. Here we investigate this quantum critical point between R = Nd and Pr with a new doping strategy, replacing Eu³⁺ with larger La³⁺ in Eu₂Ir₂O₇, to produce (Eu_1-xLa_x)₂Ir₂O₇ with an expanded lattice. On doping to x = 0.5, a large lattice parameter is achieved that is equivalent to the critical point. We can then systematically study the magnetism which arises solely from the Ir-sublattice and see how it evolves with increasing chemical pressure on. Magnetic susceptibility studies show a field cooled, zero field cooled splitting at T_c, and the systematics of these dependencies in the vicinity of the quantum critical point will be presented and discussed.