Magnon specific heat of single-crystal borocarbidesRNi2B2C

M. El Massalami

¹

,

R.E. Rapp

²

,

Francisco A. Chaves

³

et al.

Abstract

Zero-field specific heats of the single crystals RNi 2 B 2 C (RϭEr, Ho, Dy, Tb, Gd͒ were measured within the temperature range 0.1 KϽTϽ25 K. Linearized spin-wave analysis was successfully applied to account for and to rationalize the thermal evolution of the low-temperature magnetic specific heats of all the studied compounds ͑as well as the one reported for TmNi 2 B 2 C) in terms of only two parameters, namely, an energy gap ⌬ and a characteristic temperature . The evolution of and ⌬ across the studied compounds correlates very well with the known magnetic properties. , as a measure of the effective Ruderman-Kittel-Kasuya-Yosida exchange couplings, scales reasonably well with the de Gennes factor. ⌬, on the other hand, reflects predominately the anisotropic properties: ϳ2 K for GdNi 2 B 2 C, ϳ6 K for ErNi 2 B 2 C, ϳ7 K for TbNi 2 B 2 C, and ϳ8 K for each of HoNi 2 B 2 C and DyNi 2 B 2 C. The equality in ⌬ of HoNi 2 B 2 C and DyNi 2 B 2 C, coupled with the similarity in their magnetic configurations, indicates that a variation of x in the solid solution Ho x Dy 1Ϫx Ni 2 B 2 C (xϽ0.8 and T c ϽT N ) would not lead to any softening of ⌬. This supports the hypothesis of Cho et al. ͑Ref. 35͒ concerning the influence of the collective magnetic excitations on the superconducting state. This work underlines the importance of spin-wave excitations for a valid description of low-temperature thermodynamics of borocarbides.

Specific heat investigation on the magnetic phase diagrams of RNi2B2C (ElMassalami1, Saeed2, Chaves3 et al. 2010Journal of Magnetism and Magnetic MaterialsSelf Cite0000View full textAdd to dashboardCite

“…(1) and the obtained fit parameters are D a ¼ 2:9 7 0:1 K and D ¼ 5:6 70:1 K which are close to the values reported in Ref. [19]. As both D a and D a are field independent, then the insertion of these values into Eq.…”

“…Field-dependent magnon specific heat of RNi 2 B 2 C A theoretical expression for the description of the zero-field C mag ðT; HÞ of the AFM-ordered borocarbide have been reported previously [19]. Along similar theoretical considerations we calculated the field-dependent C mag ðT; HÞ of these AFM samples for the low-field limit wherein the applied field is lower than that of the spin flop field ðH o H sf Þ.…”

Effect of pressure on the superconducting properties and magnetism in HoNi2B2C

“…This result means the effect of pressure on spin fluctuation is small because A is related to the magnitude of spin fluctuation. The magnitude of A is smaller than the value A = 3.0 × 10 −3 cm K −2 , which is expected from Kadowaki-Woods plot and by using the value γ = 17.5 mJ/mol K 2 [6,7]. The coefficient A is proportional to the square of the density of state of conduction electrons at Fermi level N(0) [8].…”

Anomalous low-temperature behavior of PrT2B2C and

“…For PrNi 2 B 2 C; C M ðToT N Þ evolves as 0:13ð1ÞT 3 J=molK indicative of a magnon contribution due to gapless spin wave excitations within a three-dimensional (3d) AF structure [20,26]: indeed PrNi 2 B 2 C orders into a 3d AF ground structure [1]. For PrCo 2 B 2 C; the expression of thermal evolution of C M ðTÞ is not as simple as that for PrNi 2 B 2 C [7].…”

“…Indeed, a resistivity of the type r m pT 2 does arise from magnon-electron scattering within a ferromagnet manifesting a gapless quadratic dispersion relation [19]. However, this is not the case for these AF borocarbides where the magnon dispersion is of the type [20] _o…”