Nuclear magnetic resonance of⁵¹V (I=⁷/₂) in lanthanide vanadates: I. The paramagnetic shifts

Nuclear magnetic resonance of 51 V (I= 7 / 2 ) has been studied at temperatures down to 1.5K in single crystals of lanthanide vanadates LnVO 4 where Ln 3+ ranges from Pr 3+ , 4f 2 to Yb 3+ , 4f 13 . The crystals are tetragonal, four molecules per unit cell, but all V 5+ sites and all Ln 3+ sites are magnetically equivalent. Measurements are made with applied fields parallel and perpendicular to the tetragonal axis, and fitted to the spin-Hamiltonian H=- gamma //h(cross)B z I z - gamma perpendicular to h(cross)(B x I x +B y I y )+P(I z 2 - 1 / 3 I(I+1)). Values for the paramagnetic shifts are used to deduce the local fields at both the V 5+ and Ln 3+ sites. These fields are compared with the dipolar values, from which the magnitude of the transferred hyperfine interaction at the V 5+ sites is deduced, together with estimates of the exchange interaction between the Ln 3+ ions. The nuclear electric quadrupole interaction for 51 V is discussed in paper II, and measurements in the antiferromagnetic phases of GdVO 4 and DyVO 4 in paper III.