AAg2M[VO4]2

Abstract

AAg 2 M[VO 4 ] 2 with A = Sr 2+ or Ba 2+ present a series of layered compounds featuring a triangular lattice of transition metal cations, M = Co 2+ or Ni 2+ , connected via nonmagnetic ortho-vanadates, which provide the magnetic superexchange within the layers. For this series of insulating compounds, ferromagnetic long-range order below 10 K is suggested by magnetization and specific heat measurements and confirmed by neutron diffraction experiments. We have investigated the impact of the spacer size of A 2+ separating the layers leading to a tilting of the vanadates and consequently inducing a change in the effective magnetic correlations. Magnetization and specific heat measurements corroborate the important dependence of the magnetic superexchange on the orientation of the vanadates and the respective spin system. Furthermore, the ground state properties of the spin systems, S = 1 (Ni 2+ ) and S = 3/2 (Co 2+ ) in their respective octahedral coordination of oxygen, are evaluated. Calculated magnetic moments of the single ion complexes agree well with the magnetic structure. We, furthermore, report the dependence of T c on applied isotropic pressure suggestive of a pressure effect on the effective ferromagnetic exchange coupling constants. In addition spectroscopic investigations probing the electronic structure of the [MO 6 ] complexes and the vibrational structure of the [VO 4 ] units are given.

Magnetic properties of the triangular lattice magnets A4B′B2O12 ( A=Ba<

“…This manifests in a low AFM transition temperature as well as a low saturation field. Alternatively, AAg 2 M(VO 4 ) 2 (A=Ba, Sr; M=Co, Ni) 22 has a stronger FM superexchange via Co…”

“…There are several examples: (i) Ba 3 CoSb 2 O 9 7-10 , with equilateral Co 2+ (effective spin-1/2) triangular lattice, exhibits a 120 degree ordered state at zero field and an up up down phase with applied field. Although its spin wave spectrum can be reasonably described by the XXZ model with a small easy plane anisotropy, the quantum spin fluctuations still lead to abnormal magnon decay and line broadening that cannot be accounted for by linear and nonlinear spin wave theories 11 ; (ii) Ba 21 is a rare TLM that shows ordering with a collinear alternating stripe pattern which could be related to its strong easy axis anisotropy; (iv) AAg 2 M(VO 4 ) 2 (A = Ba, Sr; M = Co, Ni) 22,23 are TLMs possessing ferromagnetic (FM) orderings due to superexchange via the bridging vanadates on a triangular lattice; (v) NaVO 2 24,25 is a rare TLM exhibiting ordering of the V 3+ orbitals. Consequently, this orbital ordering relieves the geometrical frustration and leads to long range magnetic ordering; (vi) shown recently, the exotic quantum spin liquid (QSL) state is realized in YbMgGaO 4 26-29 with an effective spin-1/2 Yb 3+ triangular lattice in which the spin anisotropy and next-nearest neighbor interactions play important roles.…”

Synthesis and characterization of new fluoride-containing manganese vanadates A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F

“…The vanadates differ somewhat in that they are measurably larger and most importantly, they introduce d-orbitals into the bridging ligand. [9][10][11][12][13][14][15] This has the potential to change the coupling behavior between the open shell metal ions and reverse the Goodenough-Kanamori-Anderson superexchange rules. [16,17] Thus the fuller development of the metal vanadates is clearly warranted.…”

Reactivity and Structural Defects in Glaserite‐Type Iron‐Vanadates

“…In recent years the 3d‐transition metal compounds have triggered interest as these present examples for magnetic triangular lattices with ferromagnetic, antiferromagnetic, or spin‐liquid like ground states. From substitution variants on the M site by diamagnetic ions or defect vacancies, ratio M :( M ′ or □) = 2:1, honeycomb lattices may be obtained , .…”