Magnetic susceptibility of vanadium garnets NaPb2Co2V3O12 and NaPb2Ni2V3O12

Vanadium garnets NaPb2Co2V3O12 and NaPb2Ni2V3O12 have been successfully synthesized. The X-ray diffraction experiments indicate that these compounds have the garnet structure of cubic symmetry of space group Ia3¯d(Oh10) with the lattice constant of 12.742 Å (NaPb2Co2V3O12) and 12.666 Å (NaPb2Ni2V3O12), respectively. The magnetic susceptibility of NaPb2Ni2V3O12 shows the Curie-Weiss paramagnetic behavior between 4.2 and 350 K. The effective magnetic moment μeff of NaPb2Ni2V3O12 is 3.14 μB due to Ni2+ ion at A-site and the Weiss constant is −3.67 K (antiferromagnetic sign). For NaPb2Co2V3O12, the simple Curie-Weiss law cannot be applicable. The ground state is the spin doublet E2(t26e) and the first excited state is spin quartet T14(t25e2), according to Tanabe-Sugano energy diagram on the basis of octahedral crystalline symmetry. This excited spin quartet state just a bit higher than ground state influences strongly the complex temperature dependence of magnetic susceptibility for NaPb2Co2V3O12.