We have performed a comparative study of the magnetization process and the magnetic susceptibility under pressure on a stoichiometric UCoAl single crystal and an off-stoichiometric U09Co1.05Al1.05 single crystal of the anisotropic itinerant-5f-electron metamagnet UCoAl. Both UCoAl and U0.9Co1.05Al1. 05 exhibit a metamagnetic transition to the ferromagnetic state with a magnetic moment M ≍ 0.3μB (U atom)−1 in magnetic fields applied along the c axis. The critical field Bc of the transition increases with increasing pressure and temperature. The temperature dependence of the susceptibility shows a broad maximum at a temperature T max that gradually increases with increasing pressure. At ambient pressure, the transition in UCoAl is of first order below 12 K and of second order at 12–20 K. Broadeningof the transition inU0.9Co1.05Al1.05 at low temperatures is attributed rather to a variation in the B c value over the crystal (which can be described by Gaussian distribution with a half-width of 0.7 T a...

Influence of the inhomogeneous distribution of components on itinerant-5f-electron metamagnetism in UCoAl under high pressures

Physics of anisotropic itinerant 5f-electron metamagnetism in UCo1−xTxAl (T=Fe, Ni)

Magnetic phase diagram of UCoAl

Alloying and pressure effects on itinerant-electron metamagnetism of the UCoAl-based compounds

The effect of external hydrostatic pressure on magnetic properties is studied for the UCo0.995Os0.005Al single crystal. At ambient pressure, the ground state is ferromagnetic. Even lowest applied pressure 0.11 GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition is observed only in magnetic fields along the c axis of the crystal, similar to previously studied itinerant electron metamagnet UCoAl. Temperature dependence of the susceptibility for various pressures shows a broad maximum at Tmax ~ 20 K. The experimental data are analyzed with the theory of itinerant electron metamagnetism, which considers anisotropic thermal fluctuations of the uranium magnetic moment. The observed pressure dependence of the susceptibility at Tmax and the temperature for the disappearance of the first-order metamagnetic transition are explained with the theory.

Pressure-induced itinerant electron metamagnetism in UCo 0.995 Os 0.005 Al ferromagnet

Metamagnetic transition and susceptibility maximum phenomena observed for UCoAl are discussed by the spin fluctuation model for the itinerant-electron metamagnetism. The expansion coefficients of the free energy up to the tenth power of the magnetization are determined so as to fit to the observed magnetization curve at 1.8 K. By making use of these coefficients the susceptibility maximum and the metamagnetic transition at finite temperature are estimated and compared with experiment.

V Mushnikov

Papers

Metamagnetic transition and susceptibility maximum of UCoAl