Magnetic properties of the geometrically frustrated S= 12 antiferromagnets, La2LiMoO6 and Ba2YMoO6, with the B-site ordered double perovskite structure: Evidence for a collective spin-singlet ground state

Two B-site ordered double perovskites, La2LiMoO6 and Ba2YMoO6, based on the S= 12 ion, Mo5+, have been investigated in the context of geometric magnetic frustration. Powder neutron diffraction, heat capacity, susceptibility, muon-spin relaxation (μSR), and Y 89 NMR-including magic-angle spinning (MAS) NMR data have been collected. La2LiMoO6 crystallizes in P21/n with a=5.59392(19) Å, b=5.69241(16) Å, c=7.88029(22) Å, and β=90.2601(30)° at 299.7 …