Spin and Valence Fluctuation in Eu Compounds with CaAl2Si2-Structure

Abstract

We measured the X-band electron spin resonance (ESR) in the family of ternary Eu pnictides with structure CaAl2Si2 – type (sp.gr. P3 m1). Temperature dependences of position and width of resonance line well described by the contribution of the form (T- ) ( >0) and  = TN or  = c-w; TN, c-w Neel and the Curie-Weiss temperatures). In the case c-w > TN, experiment obviously indicates the existence of a magnetic phase between the AFM and PM states and relevant quantum critical point. Exchange interaction between localized magnetic moments and the current carriers causes the broadening of the ESR line ΔδH0 and the gfactor shift ΔgK (electronic Knight shift) of Eu 2+ ions relatively free electron. It is known that linewidth of the ESR due the Dzyaloshinsky-Moriya interaction depends on the correlation length  as (/a0) (a0 lattice constant), while the symmetric anisotropic interaction as (/a0) 3 . This allows to conclude that experimental results are explained by the dominant contribution of valence and spin fluctuations caused by mentioned symmetrical anisotropic interaction.