Chapter 1 Magnetism of ternary intermetallic compounds of uranium

Giant magnetoresistance (GMR) effects are observed in several classes of bulk magnetic materials. The resistance changes at metamagnetic transitions connected with reorientation of 4f moments are only moderate due to the relatively weak coupling of the 4f and conduction electrons. Much larger GMR effects can be achieved by mechanisms involving the d states (RhFe, RCo2), though the most spectacular resistance variations are connected with metamagnetic transitions in U‐intermetallic antiferromagnets. This phenomenon can be interpreted as due to Fermi surface gapping (due to magnetic superzones) and/or due to spin‐dependent scattering in analogy with magnetic multilayers.

/pdf/giant-magnetoresistance-effects-in-intermetallic-compounds-45w399d188.pdf

Giant magnetoresistance effects in intermetallic compounds (invited)

UPdSn orders antiferromagnetically below 40 K and undergoes another magnetic phase transition at about 27 K, which is connected with a re-arrangement of the antiferromagnetic structure. The magnetic properties of UPdSn are strongly anisotropic with the c-axis as the hard-magnetization direction. For UAuSn, the maximum at 36 K in the χ(T) curve may also indicate the onset of antiferromagnetism. However, the very broad anomaly in the specific heat, the poorly resolved 119Sn Mossbauer spectra and the magnetic history phenomena at lower temperatures do not point to long-range magnetic order. The possibility of a frozen non-periodic arrangement of U magnetic moments is discussed in connection with atomic disorder within the Au-Sn sublattice. The distinction between the electron properties of UAuSn and UPdSn is reflected in the different values of the γ coefficient of the low-temperature specific heat, which is remarkably small for UPdSn (5 mJ/mol K2) in contrast to UAuSn (80 mJ/mol K2). A possible localization of the 5f states in UPdSn is envisaged.

Magnetic, Electrical, and Specific-Heat Properties of UPdSn and UAuSn

We report on high-field magnetization ( M ( B )) measurements ( B ≤ 35 T) of antiferromagnetic heavy-fermion UPd 2 Al 3 at liquid helium temperatures. The data taken on well-characterized single-crystalline samples reveal a large anisotropy. For a field directed in the hexagonal plane ( B || a -axis) a sharp jump, Δ M ⋍0.94μ B /U-atom, occurs at B c = 18.0 T, while for a field along the hexagonal axis (hard axis) the magnetization is small and almost linear up to 35 T. The jump at B c = 18.0 T for B || a reflects the antiferromagnetic phase boundary.

High-field magnetization of heavy-fermion UPd2Al3

Publisher Summary This chapter discusses the intermetallic compounds of actinides, and summarizes the electronic properties of actinide intermetallic compounds with a special emphasis on the magnetic behavior. The sequentially increasing occupation of 5f states dominates the electronic properties in the series of actinide elements. In the heavy actinides, on the other hand, the decrease of the energy due to the formation of a spin polarized (non-bonding) electronic state favors the localization of the 5f states. The specific nature of the 5f states in a particular actinide element has consequences for its magnetic and other electronic properties. The chapter also discusses the properties of binary and ternary compounds, the influence of the incorporation of H and B in intermetallic compounds, morphous and icosahedral compounds, and trans-thorium compounds where the 5f-electrons play a dominant role. Materials involving Th are included mainly in cases where they can serve as suitable "background" compounds with unoccupied 5f states.

Chapter 4 Intermetallic compounds of actinides

Electrical resistivity measurements have been performed on a series of mono- and polycrystalline U(Pt1-xPdx)3 compounds (x ⩽ 0.15) in the temperature range 1.4-300 K. On alloying with Pd the spin-fluctuation-like resistivity of pure UPt3 transforms into a more complex curve for x = 0.02 and x = 0.05 revealing a transition at 3.3 K and 5.6 K, respectively. At higher Pd concentrations (x = 0.10,0.15) the resistivity curves change to a Kondo-type of behaviour. In the same concentration range a second phase appears in the X-ray patterns.

/pdf/resistivity-of-the-heavy-fermion-u-pt-pd-3-alloys-3ujd86wu0m.pdf

Resistivity of the heavy-fermion U(Pt,Pd)3 alloys

The electrical resistivity of a single-crystalline whisker of UPdIn at 4.2 K was measured in magnetic fields up to 35 T applied along the c -axis of the hexagonal structure. The resistivity values become drastically suppressed in magnetic fields where the metamagnetic transitions appear on the magnetization curve. Taking into account these results, Fermi surface nesting due to the noncompensated antiferromagnetic structure with the propagation vector along the c -axis is suggested to be a source of the large values of the electrical resistivity in zero magnetic field.

/pdf/magnetoresistance-and-metamagnetic-transitions-in-updin-74xjylsae5.pdf

A.J. Riemersma

Papers

Resistivity of the heavy-fermion U(Pt,Pd)3 alloys

Magnetoresistance and Metamagnetic Transitions in UPdIn

Hall effect of single-crystalline U(Pt,Pd)3 in high magnetic fields