Seminarium Oddziału Badań Magnetyków

13:30 czwartek, 06-06-19
sala nr 6 (bud. II)

Anisotropic low-temperature thermodynamic and magnetotransport properties of single-crystalline UCoSi2

dr hab. Daniel Gnida

UCoSi2 belongs to the family of ternary uranium silicides UTSi2 (T = Fe, Co, Ni, Pt) crystallizing with an orthorhombic crystal structure of the CeNiSi2-type [1]. Recently, it was found for UCoSi2 that its specific heat divided by temperature is proportional to –logT between 2 and 10 K, which could be considered as a non-Fermi liquid behavior [2]. Taking into account that gradual suppression of ferromagnetism in the solid solution UNi1-xCoxSi2 (0 < x < 1) occurs in the vicinity of x » 1, it was suggested that the ground state properties of UCoSi2 can be related to the closeness to quantum critical point governed by the ferromagnetic spin fluctuations [2].

To clarify the actual nature of the anomalous specific heat behavior in UCoSi2 we investigated  the low temperature properties of single crystals grown in a tetra-arc furnace using Czochralski method. Magnetic susceptibility (c), magnetization (s) and electrical resistivity (r) measurements were carried out in three principal crystallographic direction of the orthorhombic unit cell.

The results revealed that UCoSi2 exhibits strongly anisotropic properties. Exemplarily,  the b-axis component of the electrical resistivity tensor is markedly different from the resistivity measured along the crystallographic directions a and c. The temperature variation rb(T) shows logT slopes above Tmax ≈ 24 K and below Tmin ≈ 2 K, reminiscent of Kondo lattices. At the lowest temperatures, rb(T) is of Fermi liquid type. The crossover temperature from logT to T2 dependencies defines the Kondo energy scale TK ≈ 1 K.

While the overall behavior of the b-axis resistivity may point to fairly localized nature of the 5f electrons in UCoSi2, the temperature variations of the c and a components of the resistivity tensor are reminiscent of spin fluctuation systems, like UAl2 [3], UPt3 [4] or Coles alloys [5].  The rc(T) exhibits a knee at Tsf = 1.4 K that can be considered as the spin fluctuation temperature. Remarkably, the value of Tsf is similar to that of TK derived from rb(T). At lower temperatures, rc is proportional to AT2, as expected for scattering conduction electrons on spin fluctuations. The coefficient A decreases in strong magnetic fields, however the T2 behavior is preserved even in 14 T.


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