Spin-glass-like H-T phase diagram for the frustrated insulator CsNiFeF6

Abstract

The authors present DC magnetisation measurements for CsNiFeF6, which is a non-dilute random frustrated compound. They found that the maximum of the field-cooled curves occurs at TM(h) given by h=4/51/2 (1-TM(h)/TM(0))3/2, where h=g mu BSeff/3kBTM(0)(1-J0), with J0=0.7 (the mean value of the magnetic interaction distribution), the value of Seff being determined from the slope of the H/M against T curve above TM(0). The difference between the field-cooled and zero-field-cooled curves makes possible the determination of two temperatures: (i) TR1(h), below which the irreversibilities appear (TR1(h)>TM(h) for the lowest values of h); and (ii) TR2(h), below which the irreversibilities increase rapidly (TR2(h)<TM(h)). In the vicinity of h=0, the slope of the line TR1(h) goes to infinity, whereas the slope of TR2(h) goes to zero. The difference between TR1(h) and TR2(h) is large even for the lowest values of h. If a small planar anisotropy for the Ni2+ ions is assumed, the two lines can be viewed as reflecting the freezing of the transverse and longitudinal components of the spins, respectively.