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 CaAl 2 Si 2type (sp.gr. P3¯m1). Temperature dependences of position and width of resonance line well described by the contribution of the form (T- ) -1/2 ( >0) and  = T N or  =  c-w ; T N ,  c-w -Neel and the Curie-Weiss temperatures). In the case  c-w > T N , 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 ΔδH 0 and the gfactor shift Δg K (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 (/a 0 ) (a 0 -lattice constant), while the symmetric anisotropic interaction as (/a 0 ) 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.

Spin fluctuation induced Weyl semimetal state in the paramagnetic phase of EuCd 2 As 2

“…Nevertheless, ESR measurements reveal that the resonance field (H Res ) starts to decrease around 100 K (Fig. 1E), indicating that (i) an effective internal magnetic field develops as the magnetic fluctuations slow down (27) and (ii) there is a relatively large scale for the magnetic interactions, most likely associated with strong coupling in the a-b plane. However, the c −1 (T) curves exhibit positive but much lower Curie-Weiss temperatures T CW of the same order as T N , both for magnetic fields (H) applied in the a-b plane or along the c axis ( Fig.…”