Phase diagram of UGe₂.:Whether there are quantum phase transitions ?

Abstract

The phase diagram of several itinerant ferromagnets reveals the common feature. The phase transition temperature decreases with pressure increase and reaches zero value at some critical pressure Pc such that at low enough temperatures one can expect critical behavior specific for quantum phase transition. It is not the case, however. Being the second order at ambient pressure the transition from paramagnetic to ferromagnetic state at high pressures -low temperatures is transformed to the discontinuous jump.We discuss the magneto-elastic mechanism of development of the first order type instability at the phase transition to the ferromagnet state in strongly anisotropic ferromagnet UGe2. Using the parameters characterizing the properties of UGe2 we argue the effectiveness of this mechanism transforming the very weak first order type transition to the really observable one.

Unconventional critical scaling of magnetization in ferromagnetic uranium superconductorsUGe2and URhGe

“…Recently, the pressure effect on the ferromagnetic transition has been re-considered from different points of view. When the ferromagnetic transition temperature is strongly pressure-dependent, the magneto-elastic interaction or the critical fluctuation of the order parameter provides development of the first order instability at the phase transition [65][66][67]. Neutron Larmor diffraction study reveals that magneto-elastic coupling is strengthened at the pressures where superconductivity appears in UGe 2 [68].…”

Superconductivity in uranium ferromagnets

“…where M k = M (r)e −ikr d 3 r. The last term in this expression corresponds to magnetostatic energy [35,105]. The corresponding thermodynamic potential and the specific heat found in the similar uniaxial segnetoelectric model are [106]…”

“…Then, we consider the phase transition to ferromagnetic state in UGe 2 [35] and in Fermi liquid. Finally, we expose the general structure of superconducting ordering in ferromagnetic metals without inversion symmetry as it is in UIr.…”

Topological properties of ferromagnetic superconductors

“…In this paper, we argue that a promising area for observing time-reversal invariant topological superconductivity is, ironically, in systems that exhibit a coexistence of ferromagnetism and superconductivity [6][7][8][9][10][11][12][13] . Examples of materials in this category include UGe 2 14,15 , URhGe [16][17][18] , and UCoGe 14,[19][20][21][22] .…”