Specific Heat of the Spin-Fluctuation System UAl2

Abstract

We report measurements of the specific heat of paramagnetic UA1 2 between 0.8 and 25 K in magnetic fields up to 43 kOe. A nearly field-independent T 3 lnT term dominates the temperature region below 10 K. The susceptibility was measured between 3 and 10 K and varies as 1-AT 2 . These results, and earlier resistivity measurements, are consistent with the predictions of the spin-fluctuation model. This is the first unambiguous observation of the specific heat predicted by the spin-fluctuation model for an atomic ally ordered paramagnet.Experimental verification of the existence of persistent spin fluctuations in exchange-enhanced paramagnets has been unsuccessful for the most part. In particular, the theoretically predicted contributions to the specific heat and magnetic susceptibility had never been unambiguously observed in any uniform metal prior to this work. 1 In this Letter we report low-temperature measurements of the specific heat and susceptibility of the narrow-band intermetallie compound UA1 2 which strongly support the theoretical calculations and indicate the presence of spin fluctuations associated with a narrow 5/ band. The existence of a low-temperature resistivity proportional to T 2 previously led to the proposal of spinfluctuation scattering in UA1 2 . 2 The spin-fluctuation modification of the electronic specific heat has been considered by a number of authors G Doniach and Engelsberg 3 and Berk and Schrieffer 4 have shown that the absorption and re-emission of spin fluctuations renormalizes the electronic self-energy, leading to an enhanced effective mass at low temperatures. This effect manifests itself as a low-temperature enhancement of the electronic specific-heat coefficient, y, which falls off with increasing temperature as T 3 ln(T/T SF ) for T«T SF . Here T S ?=T ¥ /S is the characteristic spin-fluctuation temperature, and T F and S are the degeneracy temperature of the band and the Stoner exchange-enhancement factor. Brinkman and Engelsberg 5 and BealMonod, Ma, and Fredkin 6 showed that this effect will be nearly insensitive to the presence of an external field.Exchange-enhanced pure metals, notably Pd, exhibit enhanced low-temperature values of y, but a spin-fluctuation contribution to the enhancement is difficult to separate from that due to the electron-phonon interaction, and quantitative comparisons with spin-fluctuation theory have been largely unsuccessful. The known spin-fluctuation system He 3 exhibits a T 3 lnT term in the specific heat at very low temperatures, 7 but such terms have not been observed in any metal prior to this worko 8 Very large exchange enhancements are found in some alloys near the critical concentration for ferromagnetism. Up turns in C/T for CttNi and RhNi have been fitted by T 3 InT terms and attributed to spin fluctuations. 9 ' 10 However, these effects are now known to be due to magnetic clustering (superparamagnetism)o 1,11 In the case of RhNi this was demonstrated by the observation that the upturn in C/T is suppressed by applied fields much smaller...

Electronic specific heat inBaFe2−xNixAs2

“…The low temperature upturn below 15 K may be attributed to the Cr impurities 31 . Treated as a diluted spin system, we may fit the low-temperature data with the spin-fluctuation theory as follows 34,35 ,…”

“…While the decrease of γ n at in the underdoped regime seems to be related to the Fermi surfaces reconstruction due to the presence of AF order 7 , the weakening of electronic correlation with Ni doping may cause the reduction of γ n in the overdoped regime 41 . The spinfluctuation contribution to the mass enhancement is 1 + 9 2 ln(S/3) 34 , which gives value of the Stoner exchangeenhancement factor S between 3.7 to 4.7 around optimal doping level. It should be noted that the above analysis may be too simplified considering the multi-band and correlated nature of iron-based superconductors.…”

Electronic, magnetic, and electric transport properties of Ce3Rh4Sn13and CeŚlebarski1, White2, Fijałkowski3 et al. 2012Phys. Rev. B

“…La 3 Rh 4 Sn 13 superconducts below a critical temperature T c = 2.6 K. Moreover, the magnetic susceptibility, measured between T c and 300 K in a magnetic field of 0.1 T, obeys a T 2 -dependence very well, indicating the presence of ferromagnetic spin-fluctuations (as presented in panel (b)). A spin fluctuation characteristic temperature T SF ∼ 1090 K is estimated by analyzing the data with the spin-fluctuation model 27 Figs. 6-8 compare the low-temperature specific heat of Ce 3 Rh 4 Sn 13 and Ce 3 Co 4 Sn 13 .…”

Heavy fermion behavior in uranium compounds

“…It is hoped that some kind of Fermi liquid description will apply to the heavy fermion state at low enough temperature. This regime is probably reached in the case of the spin-fluctuators UA12 [6] and UPt 3 [7] near 1 K where the temperature variation of the electrical resistivity is approaching T 2 as expected for a Fermi liquid ( fig. 4) [8].…”