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

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The properties of the spin density fluctuations in the itinerant antiferromagnetic compounds V₃Se₄ and V₅Se₈ 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/T₁ of ⁵¹V for both V₃Se₄ and V₅Se₈ 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/T₁ observed in V₅Se₈ 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.