Critical behavior of magnetization in URhAl:Quasi-two-dimensional Ising system with long-range interactions

Abstract

The critical behavior of dc magnetization in the uranium ferromagnet URhAl with the hexagonal ZrNiAl-type crystal structure has been studied around the ferromagnetic transition temperature T_C. The critical exponent beta for the temperature dependence of the spontaneous magnetization below T_C, gamma for the magnetic susceptibility, and delta for the magnetic isotherm at T_C have been obtained with a modified Arrott plot, a Kouvel-Fisher plot, the critical isotherm analysis and the scaling analysis. We have determined the critical exponents as beta = 0.287 +- 0.005, gamma = 1.47 +- 0.02, and delta = 6.08 +- 0.04 by the scaling analysis and the critical isotherm analysis. These critical exponents satisfy the Widom scaling law delta=1+gamma/beta. URhAl has strong uniaxial magnetic anisotropy, similar to its isostructural UCoAl that has been regarded as a three-dimensional (3D) Ising system in previous studies. However, the universality class of the critical phenomenon in URhAl does not belong to the 3D Ising model (beta = 0.325, gamma = 1.241, and delta = 4.82) with short-range exchange interactions between magnetic moments. The determined exponents can be explained with the results of the renormalization group approach for a two-dimensional (2D) Ising system coupled with long-range interactions decaying as J(r)~r^-(d+sigma) with sigma = 1.44. We suggest that the strong hybridization between the uranium 5f and rhodium 4d electrons in the U-Rh_I layer in the hexagonal crystal structure is a source of the low dimensional magnetic property. The present result is contrary to current understandings of the physical properties in a series of isostructural UTX uranium ferromagnets (T: transition metals, X: p-block elements) based on the 3D Ising model.

11 pages, 8 figures

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Cited by in corpus (5)

• Ferromagnetism on an atom-thick and extended 2D-metal-organic framework
• Negative thermal expansion and itinerant ferromagnetism in Mn${}_{1.4}$Fe${}_{3.6}$Si${}_3$
• Novel critical behavior of magnetization in URhSi:Similarities to uranium ferromagnetic superconductors UGe${}_2$ and URhGe
• Localization of 5f-electrons and pressure effects on magnetism in U intermetallics in the light of spin-fluctuation theory
• Different universality classes of isostructural U$TX$ compounds ($T$ = Rh, Co, Co${}_{0.98}$Ru${}_{0.02}$; $X$ = Ga, Al)