Magnetic frustration in lead pyrochlores

Abstract

The rich phase diagrams of magnetically frustrated pyrochlores have maintained a high level of interest over the past 20 years. To experimentally explore these phase diagrams requires a means of tuning the relevant interactions. One approach to achieve this is chemical pressure, that is, varying the size of the non-magnetic cation. Here, we report on a new family of lead-based pyrochlores A2Pb2O7 (A = Pr, Nd, Gd), which we have characterized with magnetic susceptibility and specific heat. Lead is the largest known possible B-site cation for the pyrochlore lattice. Thus, these materials significantly expand the phase space of the frustrated pyrochlores. Pr2Pb2O7 has an absence of long-range magnetic order down to 400 mK and a spin ice-like heat capacity anomaly at 1.2 K. Thus, Pr2Pb2O7 is a candidate for a quantum spin ice state, despite weaker exchange. Nd2Pb2O7 transitions to a magnetically ordered state at 0.41 K. The Weiss temperature for Nd2Pb2O7 is θCW = −0.06 K, indicating close competition between ferromagnetic and antiferromagnetic interactions. Gd2Pb2O7 is a Heisenberg antiferromagnet that transitions to long-range magnetic order at 0.81 K, in spite of significant site mixing. Below its ordering transition, we find a T 3/2 heat capacity dependence in Gd2Pb2O7, indication of a ground state that is distinct from other gadolinium pyrochlores. These lead-based pyrochlores provide insight into the effects of weakened exchange on highly frustrated lattices and represent further realizations of several exotic magnetic ground states which can test theoretical models.

Structural and magnetic properties of two branches of the tripod-kagome-lattice familyA2R3Sb3O14(ADun1, Trinh2, Lee3 et al. 2017Phys. Rev. B4713583View full textAdd to dashboardCite

“…5(b)) yields θ W = -0.01 K, µ ef f = 2.38 µ B for MgNd and θ W = -0.11 K, µ ef f = 2.28 µ B for ZnNd. These numbers are similar to that of the Nd pyrochlore 40,41 and consistent with a recent report of the MgNd 26 . For MgNd, a broad peak is observed in the zero field χ ac at 0.49 K, accompanied by a shoulder around 0.55 K (Fig.…”

Spin correlations in the dipolar pyrochlore antiferromagnet Gd2Sn2O7

“…Such experiments are challenging, however, because of the difficulty of preparing large single crystals of Gd 2 Sn 2 O 7 and the large neutronabsorption cross-section of natural Gd. Our observation that the powder diffusescattering profile is sensitive to the weak further-neighbour interactions that select a particular ordered state may be relevant to the related materials Gd 2 Pb 2 O 7 [44], Gd 2 Pt 2 O 7 [45], and Gd 2 Ti 2 O 7 , in which the nature of the magnetic order is not yet conclusively established [7,46,47]. Careful measurement of the powder I(Q) could allow accurate determination of the further-neighbour exchange interactions, allowing the nature of long-range order to be predicted in these systems.…”

Sensitivity of magnetic properties to chemical pressure in lanthanide garnetsLn3A2X3O12,Ln = Gd, Tb, Dy, Ho,A = Ga, Sc, In, Te,X = Ga, Al, Li

“…Such studies have been extensively carried out for the highly frustrated lanthanide pyrochlores, Ln2B2O7 (B = non-magnetic cation), where the dominant interactions are the nearestneighbour exchange, the dipolar interaction and CEF effects. While the pyrochlores with Ln = Dy, Ho remain in the spin ice state for different B cations, varying the chemical pressure radically changes the magnetic ground state for Ln = Tb, Yb, Gd [9][10][11][12][13][14][15]. The Ln 3+ lie at the vertices of corner-sharing equilateral triangles forming two interpenetrating ten-membered rings.…”