Neutron scattering and muon-spin spectroscopy studies of the magnetic triangular-lattice compounds <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>A</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>La</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>NiW</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>12</mml:mn></mml:msub><mml:mspace width="0.28em" /><mml:mrow><mml:mo>(</mml:mo><mml:mi>A</mml:mi><mml:…

We report on the geometrically frustrated two-dimensional triangular-lattice magnets ${A}_{2}{\mathrm{La}}_{2}{\mathrm{NiW}}_{2}{\mathrm{O}}_{12}$ ($A=\mathrm{Sr},\mathrm{Ba}$) studied mostly by means of neutron powder diffraction (NPD) and muon-spin rotation relaxation ($\ensuremath{\mu}\mathrm{SR}$) techniques. The chemical pressure induced Ba-for-Sr substitution suppresses ferromagnetic (FM) transition from 6.3 K in Ba compound to 4.8 Sr compound. find that $R\overline{3}$ space group reproduces NPD patterns better than previously reported $R\overline{3}m$ group. Both compounds adopt same magnetic structure with a propagation vector $\mathbit{k}=(0,0,0)$, which ${\mathrm{Ni}}^{2+}$ moments are aligned ferromagnetically along $c$ axis. zero-field $\ensuremath{\mu}\mathrm{SR}$ results reveal two distinct internal fields (0.31 0.10 T), caused long-range FM order. small transverse rates reflect homogeneous field distribution ordered phase and, thus, further support simple arrangement moments. longitudinal rates, both paramagnetic states ${A}_{2}{\mathrm{La}}_{2}{\mathrm{NiW}}_{2}{\mathrm{O}}_{12}$, indicate spin fluctuations rather weak. Our demonstrate indeed changes superexchange interactions compounds, being dominant.