THE ORDER OF THE NÉEL TRANSITION IN Cr AND DILUTE Cr ALLOYS WITH V AND Re

Abstract

The weak first-order Néel transition in Cr was explained by Young and Sokoloff (1974) as being associated with the strain-wave second harmonic of the spin-density wave (SDW). Kotani (1975) developed a theory of higher harmonics of the SDW in Cr and its dilute alloys, which indicates an inverse relation between the amplitude of the strain wave and the value of the incommensurability parameter, δ=1−Q, Q being the SDW wave vector. This effect was observed by Iida et al. (1981), who found that the strain-wave amplitude A2/S1 relative to that of the SDW decreases as V is doped into Cr and δ increases, but remains roughly constant in CrMn alloys as δ decreases and the system approaches commensurability. The ratio S3/S1 of the amplitudes of the third harmonic and the fundamental, on the other hand, increases progressively more rapidly as δ decreases. The present work confirms that the magnitude of the first-order step in S1 at the Néel transition is roughly the same in Cr+0.18 at % Re as in pure Cr (Lebech and Mikke 1972), the values of δ at the transition being 0.32 and 0.35, respectively, whereas in Cr+0.2 at % V having δ=0.42 the Néel transition is continuous.