Specific heat of uniaxial spin glasses in the mK range and fields of 6 T (abstract)

摘要

The magnetic contribution to the specific heatCm(T) of polycrystalline Isinghyphen;like spin glasses (SG)ScEr(1.05; 2.5 at.thinsp;percnt; Er) andZnMn (195, 270 ppm Mn) has been measured in the temperature range 0.1T2.5 K, using a nonadiabatic heat pulse method.Cm(T) of thexhyphen;yndash;like SGCdMn (488 ppm Mn) has been measured on single crystals in external fields (Bexle;6thinsp;T) withBexeither perp; or par; to thecaxis. The data are compared with susceptibility measurements.1For all samples the behavior ofCm(T) is similar to that in archetypal SGrsquo;s. There is scaling and a linear dependenceCm(T) forTrarr;0. The highhyphen;temperature data do not follow a simple 1/Tor 1/T2law. In contrast to the results from meanhyphen;field calculations for uniaxial systems we find no peaks inCm(T). Yet, the relatively sharp maxima inCm(T) atTmofScEr andZnMn are close to the freezing temperaturesTpar;g. InCdMnthinsp;Tperp;gfrom khgr;(T) lies well belowTm. The data forScEr andZnMn can be fitted within a twohyphen;level system model. ForCdMnCmis stronglydependent onBexand shows anisotropic behavior. ForBexperp;thinsp;c(parallel to the easy axis)Cm(T,B) is SGhyphen;like forallfields and comparable to isotropic SGrsquo;s. With increasing fieldsTmshifts to higher temperatures and the slope in the linear range decreases. ForBexpar;c(hard direction) the behavior is quite different. ForBex2 T the linear slope inCm(T) andTmare only weakly dependent onBex. Increasing the field leads to a remarkable reduction ofCm(T) aroundTm, andCm(T) becomes nonlinear forTrarr;0. This can be understood in terms of new meanhyphen;field calculations on anisotropic Isinghyphen;SGrsquo;s by Usadel,2who predicts a breakdown of the SG interactions in strong magnetic fields transverse to the easy axis.