NMR Investigations on the Spin Fluctuations in Itinerant Antiferromagnets. I. V3Se4 and V5Se8

The properties of the spin density fluctuations in the itinerant antiferromagnetic compounds V 3 Se 4 and V 5 Se 8 have been investigated in both the paramagnetic and the antiferromagnetic states by using the pulsed NMR technique. The temperature dependences of the uniform susceptibilities χ u ( T ), the staggered moments M Q ( T ) and the nuclear spin-lattice relaxation rates 1/ T 1 of 51 V for both V 3 Se 4 and V 3 Sa 8 are well explained within a framework of the self-consistent renormalization (SCR) theory of spin fluctuations for weak itinerant antiferromagnets. The Curie-Weiss like behavior of χ u ( T ) and the temperature independent contribution to the 1/ T 1 observed in V 5 Se 8 are concluded to be due to the effect of the spin fluctuation components around q =0 which, in addition to those around q = Q ( Q being antiferromagnetic wave vector), play an important role in determining the magnetic properties.