Magnetism on the stretched diamond lattice in lanthanide orthotantalates

Abstract

The magnetic lanthanide (Ln 3+ ) ions in the fergusonite and scheelite crystal structures form a distorted or stretched diamond lattice which is predicted to host exotic magnetic ground states. In this study, polycrystalline samples of the fergusonite orthotantalates M-LnTaO 4 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) were synthesized and then characterized using powder diffraction and bulk magnetometry and heat capacity. TbTaO 4 orders antiferromagnetically at 2.25 K into a commensurate magnetic cell with k = 0, magnetic space group 14.77 (P2 1 /c), and Tb moments parallel to the a axis. No magnetic order was observed in the other materials studied, leaving open the possibility of exotic magnetic states at T < 2 K.

Enhanced cryogenic magnetocaloric performance and the existence of short-range magnetic correlations in frustrated diamond geometries

“…This shows that all the compounds crystallize in a monoclinic structure with space group I2/a (#15). The obtained lattice parameters and atomic positions are summarized in table 1, and are in good agreement with previous reports [26,29]. Figure 2(a) represents the crystal structure of the studied compounds, consisting of (Gd/Dy)O 8 and (Ta/Nb)O 6 units.…”

“…The observed values of D a are 40.0%, 38.8% and 37.9% for GTO, GNO and DNO, respectively. According to Kelly et al [26], using the nomenclature of harmonic honeycomb series ( H ⟨N⟩), the stretched diamond lattice can be considered as a truncated form of a hyperhoneycomb structure and is represented as H ⟨−1⟩. Similar to the members of the H ⟨N⟩ series, the magnetic properties of a H ⟨−1⟩ lattice are governed by the interplay of nearest-neighbour (J nn ) and next-nearest-neighbour (J nnn ) interactions.…”

“…However, our system's R(Ta/Nb)O 4 can be prepared by a solid state reaction technique under ambient pressure. GdTaO 4 , GdNbO 4 and DyNbO 4 crystallize in a monoclinic structure, wherein magnetic (rare earth) ions form a three-dimensionally connected stretched diamond lattice, which is a prototype of highly frustrated three-dimensional (3D) systems [25,26]. Here, we would like to mention that diamond geometries are usually observed in transition metalbased spinels.…”