Magnetic ground state of the pyrochlore oxide ${\mathrm{Y}}_2{\mathrm{Nb}}_2{\mathrm{O}}_7$

We report dc magnetization and specific heat of a series of insulating pyrochlore oxides ${\mathrm{Y}}_2{\mathrm{Nb}}_{2-x}{\mathrm{Ti}}_x{\mathrm{O}}_7.$ Although the end member ${\mathrm{Y}}_2{\mathrm{Nb}}_2{\mathrm{O}}_7$ contains magnetic tetravalent Nb ions ${(4d}^1,$ $S=1/2),$ it does not exhibit any sign of magnetic ordering at least between 0.35 and 800 K. In addition, it exhibits Curie-Weiss behavior originating from spins $S=1/2\mathrm{}$ on less than 0.3% of the Nb sites; the remaining spins of Nb ions apparently disappear. With the substitution of nonmagnetic Ti ions, this magnetic component increases only up to 4.7% of the B sites, with Nb and Ti combined. These results are ascribable to a strongly correlated spinless state, which is a specific character derived from a band structure of d-electron pyrochlore oxides.