Glassy Behavior and Isolated Spin Dimers in a New Frustrated Magnet BaCr9pGa12−9pO19

Abstract

Using bulk susceptibility and neutron scattering techniques, we have studied a new frustrated magnet, BaCr9pGa12−9pO19 [BCGO(p)], with \(0.4 \lesssim p \lesssim 0.9\). This system is isostructural to SrCr9pGa12−9pO19 [SCGO(p)], in which the magnetic Cr3+ (3d3, s = 3/2) ions form a quasi-two-dimensional triangular lattice of bi-pyramids or kagome–triangle–kagome trilayers. Our bulk susceptibility data exhibit glassy behavior at temperatures much lower than the absolute values of the Curie–Weiss temperature ΘCW ≈ −695(1) K for BCGO(p = 0.902(8)). The frustration index |ΘCW|/Tf is as high as 190 for BCGO(p = 0.902(8)) indicating strong frustration. Our inelastic neutron scattering data on BCGO(p = 0.902(8)) reveal a dispersionless magnetic excitation centered at ħω = 16.5(1) meV, due to a singlet to triplet excitation of spin s = 3/2 dimers. The spin dimers are formed by Cr3+ ions in two 4fvi layers that lie between 12k–2a–12k (kagome–triangle–kagome) trilayers. These results indicate that BCGO(p) is another...