Study of magnetic defects in Nb2VSbO10

Magnetic properties of Nb2VSbO10, the compound formed in V-Sb-Nb oxide system, were investigated by dc magnetisation measurements using an MPMS-7 SQUID magnetometer and EPR conventional X-band Bruker E 500 spectrometer. Although the nominal valences of the constituting metal ions indicated a diamagnetic material, Nb2VSbO10 displayed rich and interesting magnetic behaviour due to the existence of numerous defects related to oxygen vacancies. Isothermal magnetisation has revealed the presence of three spin subsystems - two different paramagnetic systems and antiferromagnetic spin clusters. EPR spectra showed the presence of three components, involving isolated and interacting V4+ ions as well as antiferromagnetic spin clusters. All these magnetic defects are the result of valence changes of metal ions due to charge compensation in the neighborhood of oxygen vacancies, most probably located on grains boundaries.