High pressure synthesis and characterization of R₂Pt₂O₇ pyrochlores

Rare-earth pyrochlore oxides R₂B₂O₇ constitute a versatile material platform to study a wide range of magnetic phenomena including order by disorder, geometric frustration, spin ice, and spin freezing. While being non-magnetic, the B-site cations are thought to be able to influence the magnetic properties of these compound primarily through the chemical pressure, which has been well demonstrated in the comparative studies of R₂B₂O₇ (B = Ge, Ti, Sn) through varying the radius of the B-site cation. The high-pressure synthesis of R₂Ge₂O₇ with the cubic pyrochlore structure is essential for these studies. Recently, we have further extended our research to the R₂Pt₂O₇ system, which can only be stabilized under high-pressure conditions. Unlike the previously studied R₂B₂O₇ with the B site occupied by either a 3d transition-metal like Ti or a p-block metal such as Ge and Sn, the Pt⁴⁺ has spatially more extended 5d orbitals and thus enhanced Pt 5d-O 2p hybridizations that might modify the local anisotropic exchange interactions of R3+ ions. Such an effect beyond the steric effect has not been taken into account in previous studies on the geometrically frustrated magnets. Indeed, we found enhanced magnetic ordering temperature in Gd₂Pt₂O₇ due to presence of extra superexchange pathways through the empty Pt-e_g orbitals [1]. We also revealed distinct influences on the anisotropic exchange interactions in the XY pyrochlores Er₂Pt₂O₇ and Yb₂Pt₂O₇ [2]. In addition, we observed unusual behaviors in the classical spin ice Ho₂Pt₂O₇ [3].
References:
[1] Phys. Rev. B 94, 214429 (2016)
[2] Phys. Rev. B 93, 014443 (2016)
[3] Manuscript in preparation.