Magnetic frustration on a Kagomé lattice in R₃Ga₅SiO₁₄langasites with R = Nd, Pr

Abstract

In the R 3 Ga 5 SiO 14 compounds, the network R of rare earth cations form well separated planes of corner sharing triangles topologically equivalent to a kagomé lattice. Powder samples and single crystals with R = Nd and Pr were prepared and magnetostatic measurements were performed under magnetic field up to 10 T in the temperature range from 1.6 K to 400 K. Analysis of the magnetic susceptibility at the high temperatures where only the quadrupolar term of the crystal electric field prevails, suggests that the Nd and Pr magnetic moments can be modeled as coplanar elliptic rotators perpendicular to the three fold axis of the crystal structure that interact antiferromagnetically. Nonetheless, a disordered phase that can be ascribed to geometric frustration persists down to the lowest temperature which is about 25 times smaller than the energy scale for the exchange interactions.

Spin-cluster excitations in the rare-earth kagome systemNd3Ga5SiO14

“…1.The straight lines drawn through the data points give θ CW ~ -20 K which is roughly a factor of 2 lower than values suggested by previous work. 9,15,16 As pointed out above, extrapolation of high temperature data is strongly dependent on the temperature range used to fit data. The straight lines through the data points are guides to the eye and do not provided reliable values for θ CW .…”

“…13 There is uncertainty concerning the value of the frustration factor f in NGS. An estimate based on a linear fit to the inverse magnetic susceptibility (1/χ) versus T plot at high temperatures (200 -400 K) gives a Curie-Weiss temperature θ CW ~ -55 K 9,15,16 and, correspondingly, a comparatively high value for f (> 1000). The high-temperature linear extrapolation used in 1/χ plots can often lead to a considerable overestimate of the magnitude of θ CW as a result of the role played by population/depopulation of high energy crystal field states.…”

Ground State of the Easy-Axis Rare-Earth Kagome LangasitePr3Ga5SiO14

“…Beyond the Ising model on the kagomé lattice, transverse quantum dynamics favor an unconventional semi-classical spin liquid at low temperatures [6]. Besides, under applied magnetic field, a broad magnetization plateau is predicted [7].The discovery of new members, RE 3 Ga 5 SiO 14 (RE = rare earth) [8], of the Langasite family has provided unique realizations of the easy-axis kagomé antiferromagnet for RE=Nd, Pr. Both Nd 3 Ga 5 SiO 14 (NGS) and Pr 3 Ga 5 SiO 14 (PGS) possess the same magnetic net, topologically equivalent to the kagomé lattice.…”

“…The discovery of new members, RE 3 Ga 5 SiO 14 (RE = rare earth) [8], of the Langasite family has provided unique realizations of the easy-axis kagomé antiferromagnet for RE=Nd, Pr. Both Nd 3 Ga 5 SiO 14 (NGS) and Pr 3 Ga 5 SiO 14 (PGS) possess the same magnetic net, topologically equivalent to the kagomé lattice.…”

“…From the measured width ∆/γ µ of the frozen field distribution and the relation cµ e = 2/πµ J ∆/∆ J [18], we compute c = 0.007 for µ e = µ J . In principle, it is possible that the ground state of the non-Kramers Pr 3+ ion in PGS is nonmagnetic, except at some rare sites where, because of the random Ga 3+ /Si 4+ disorder on one of the Ga sites [8], the CF would favor a magnetic ground state. This scenario, however, can be ruled out since (i) PGS is an insulator so there exists no long-range interaction that could induce a spin-glass state at 40 K for a concentration of moments far below the site percolation threshold c p = 0.65 of the kagomé lattice.…”