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

Abstract

The geometrically frustrated two dimensional triangular lattice magnets A4B'B2O12 (A = Ba, Sr, La; B' = Co, Ni, Mn; B = W, Re) have been studied by x-ray diffraction, AC and DC susceptibilities, powder neutron diffraction, and specific heat measurements. The results reveal that (i) the samples containing Co 2+ (effective spin-1/2) and Ni 2+ (spin-1) ions with small spin numbers exhibit ferromagnetic (FM) ordering while the sample containing Mn 2+ (spin-5/2) ions with a large spin number exhibits antiferromagnetic (AFM) ordering. We ascribe these spin number manipulated ground states to the competition between the AFM B'-O-O-B' and FM B'-O-B-O-B' superexchange interactions; (ii) the chemical pressure introduced into the Co containing samples through the replacement of different size ions on the A site finely tunes the FM ordering temperature of the system. We attribute this effect to the modification of the FM interaction strength induced by the change of the O-B-O angle through chemical pressure.

Nanocrystalline BaCo3(VO4)2(OH)2 with a kagome lattice of Co(ii) ions: synthesis, crystal structure and magnetic properties

“…S8, ESI† shows that the M ( H ) data at 2 K are significantly different from Brillouin equations calculated for J = 3/2 with g = 2 and for an effective J = 1/2 with g = 4, which is a typical value observed in compounds containing high-spin Co 2+ ions in a distorted octahedral environment. 8,19,21,22 Also, the value g = 4 is consistent with the theoretical expression for the g factor that can be calculated within the effective J eff = 1/2 approach. 23 The magnetization versus field variation is not saturated even at 2 K and 7 T. The maximum value of the magnetization at 2 K (40 emu g −1 ) corresponds to 1.4 μ B per Co-atom, which is lower than the saturation values observed in bulk oxides or orthovanadate compounds containing high-spin Co 2+ ions in octahedral environment.…”

“…S5, ESI,† decreases less rapidly than required by the Curie–Weiss law when decreasing temperature in the range of 150–10 K. Similar deviation from the high-temperature Curie–Weiss behaviour was reported in other octahedral high-spin Co 2+ bulk oxides, and was ascribed to the splitting between a Kramers doublet ground state with effective spin J eff = ½ and lowest excited states. 19,20…”

Spin liquids in geometrically perfect triangular antiferromagnets

“…4). With the exception of the latter, these compounds still develop long-range magnetic order [101,106]. In fact, even the Mn-based (spin- 5 2 ) analog of Ba 8 CoNb 6 O 24 reveals the 120 • order [107], whereas Ba 8 CoNb 6 O 24 itself also shows a characteristic peak in the spin-lattice relaxation rate at 0.1 K reminiscent of the magnetic ordering transition, although the NQR line does not broaden below this temperature [108].…”

Successive phase transitions and magnetization plateau in the spin-1 triangular-lattice antiferromagnet Ba2La2NiTe2O12 with small easy-axis anisotropy

“…2. First, we chose the structure parameters of Ba 2 La 2 NiW 2 O 12 [43,44] as the initial parameters of the Rietveld analysis, setting the occupancy to 1 for all atoms and the thermal vibration parameter B to 1.401Å 2 , which was reported for Ba 2 La 2 NiW 2 O 12 [43]. The analysis was based on two structural models with space groups R3m and R3.…”