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Multiaxial magnetic structures in cubic compounds: Uranium monopnictides and manganese alloys
Abstract
The inclusion of anisotropic terms of tetragonal symmetry in the exchange interaction of polyatomic cubic crystals is investigated. This explains the two kinds of multiaxial structures found in U monopnictides and Mn intermetallics on the basis of wave vector k point symmetry and configuration of the unit cell.
This document is part of Subvolume B6α 'Actinide monopnictides' of Volume 27 'Magnetic properties of non-metallic inorganic compounds based on transition elements' of Landolt-Börnstein - Group III Condensed Matter. A survey of data is provided. Substances contained in this document (element systems and chemical formulae) A-N-U: (U1-xAx)N. Am-Bi: AmBi. Am-N: AmN. Am-P: AmP. Am-Sb: AmSb. Am-X: AmX (X = N...Bi, O). An-An'-N: An1-xAn'xN (An, An' = actinide). An-As: AnAs (An = Th...Cm). An-Bi: AnBi (An = U...Cm). An-C: AnC (An = Th, U, Np, Pu, Am). An-N: AnN (An = Th...Cf). An-Sb: AnSb (An = U, Np, Pu). An-X: AnX (X = pnictogen), AnX (An = Ac...Cf; X = C, N...Bi). An-X-Y: AnX1-xYx (X = pnictogen, Y = chalcogen). An-Y: AnY (An = Th...Pu). As-Cf: CfAs. As-Cm: CmAs. As-Np: NpAs. As-P-U: UAs1-xPx. As-Pa: PaAs. As-Pu: PuAs. As-Sb-U: U(Sb1-xAsx). As-Th: ThAs, Th-ThAs. As-Th-U: U1-xThxAs. As-U: UAs, U-UAs. As-U-Y: U1-xYxAs. Bi-Cf: CfBi. Bi-Cm: CmBi. Bi-Np: NpBi. Bi-Pu: PuBi. Bi-Th: ThBi, Th-Bi. Bi-U: UBi, U-Bi. Bk-N: BkN. Bk-X: BkX (X = N...Sb). C-N-Pu: PuC1-xNx, PuN0.56C0.28. C-N-Th: ThC1-xNx. C-N-U: UN1-xCx. C-Np: NpC, NpC1-x. C-O-Pu: Pu(C, O). C-O-U: UC1-xOx. C-Pa: PaC. C-Pu: PuC, PuC1-x. C-Pu-U: (U,Pu)C. C-Th: ThC, Th-C, ThCx. C-Th-U: U1-xThxC. C-U: UC, UC1+x, UC1-x. Ce-N: CeN. Ce-X: CeX (X = pnictogen). Cf-N: CfN. Cf-Sb: CfSb. Cf-X: CfX (X = N, As, Sb, Bi). Cm-N: CmN. Cm-P: CmP. Cm-Sb: CmSb. Cm-X: CmX (X = N...Bi). Gd-X: GdX (X = N...Sb). La-Sb: LaSb. Ln-N-Th: Th1-xLnxN (Ln = Y,La, Ce, Pr, Nd). Ln-N-U: (U1-xLnx)N (Ln=La, Ce, Pr, Nd, Sm, Gd, Dy, Er). N-Np: NpN. N-Np-U: U1-xNpxN. N-O-Th: Th-N-O system. N-Pa: PaN. N-Pu: PuN, PuNx. N-Np-Pu: Np1-xPuxN. N-Pu-U: U1-xPuxN. N-Th: ThN, Th3N4. N-U: UN, U2N3. Nd-P-U: U1-xNdxP. Np-P: NpP. Np-Pu-X: (Pu, Np)X (X = pnictogen). Np-Sb: NpSb. Np-X: NpX (X = C, N...Bi). O-U: UO. P-Pr-U: U1-xPrxP. P-Pu: PuP. P-R-U: U1-xRxP (R = Pr, Pr, Nd). P-Th: ThP, Th-P, ThP0.95, ThPx. P-Th-U: U1-xThxP. P-U: UP, U-P, UP1-x. Pu-Sb: PuSb. Pu-Sb-U: U1-xPuxSb. Pu-Sb-Y: Pu1-xYxSb. Pu-X: PuX (X = As, Sb, Bi). Sb-Te-U: USb1-yTey. Sb-Th: ThSb. Sb-Th-U: U1-xThxSb. Sb-U: USb. Sb-U-Y: U1-xYxSb. Th-X: ThX (X = C, N...Bi, S). U-X: UX (X = C; N...Bi, S). U-Y: UY (Y = chalcogen).
This document is part of Subvolume B6α 'Actinide monopnictides' of
Volume 27 'Magnetic properties of non-metallic inorganic compounds based
on transition elements' of Landolt-Börnstein - Group III Condensed
Matter. It contains Figures R (General data).
Actinides and their compounds are a most fruitful test material for new theoretical ideas and for discoveries of new phenomena which enrich solid state physics in general. The physical properties of actinide compounds are reviewed with particular emphasis on their magnetic characteristics. Due to their complexity, mainly the simplest compounds are treated, some of which have properties that can be theoretically explained. The actinides discussed include: include uranium, plutonium, and neptunium compounds with NaCl-type lattice; solid solutions and other NaCl-type compounds; AnX2-type, AnXY-type and An3X4 actinide compounds; intermetallic actinide compounds; and actinide oxides and halides.
Sign reversal of the rhombohedral linear birefringence at Tc2 = 129 K is ascertained by principal refractive index data on single T-domains of antiferromagnetic α-MnS. Thus for the first time the disputed existence of a structural phase transition at Tc2 is unambiguously confirmed. It is probably connected with a transition from a compressed collinear type-II (T > Tc2) into an elongated multiaxis spin structure (T < Tc2).
The origins and consequences of magnetocrystalline anisotropy energy (MAE) and magnetoelastic coupling in terms of the electronic structure of 4f and 5f elements are reviewed. In the heavy rare-earth metals, the large molecular fields dominate and the MAE arises primarily from the crystalline electric field (CEF) with modifications due to the magnetostriction. In lighter rare earths, the molecular fields can be small and the MAE energy may then be dominated by multipolar interactions. The light actinide metals do not order magnetically, however, compounds of light actinide metals have a rich variety of magnetic ordering strongly influenced by the MAE energy and magnetoelastic effects, with CEF and multipolar interactions frequently being of the same order as exchange interactions.
Recent neutron scattering experiments have shown that the
low-temperature magnetic structures of most uranium pnictides are of the
multiple-k--> type. In order to describe these, we use a simple model
Hamiltonian consisting of an anisotropic exchange interaction between
nearest- and next-nearest-neighbor ions and a crystal-field term. We
show that the exchange determines the type (AFM-I, IA) and the
polarization of the magnetic structure. Single- and multiple-k-->
structures have the same exchange energy, though the spins are aligned
along different high-symmetry directions: The crystal field determines
which of these spin structures has the lowest energy. This model
provides an explanation for the antiferromagnetic type-I structure of
UN, UP, and USb and the type-IA structure of UAs, as well as for the
possible number of k--> components.
We develop a new approach to bilinear exchange interactions in cubic rare-earth compounds, in terms of irreducible representations of the cubic symmetry group. Within a generalized susceptibility formalism, we include isotropic and anisotropic interactions to derive the magnetic excitation modes of an antiferromagnet. The modes for a ferromagnet and paramagnet are also studied. Finally, we present dispersion curves for the longitudinal and transverse modes which show the influence of anisotropic bilinear interactions.
The magnetic structures and transformations in the ordered phases of the Mn-Pt system have been investigated in a wide concentration range by magnetic, x-ray, and neutron diffraction methods. The properties of the Mn3Pt1-yRhy and Mn3-zFezPt systems have also been studied. The triangular and the collinear antiferromagnetic structures, both found in the Mn3Pt phase, undergo a first-order transformation into each other at a critical value of the lattice parameter where the next-nearest-neighbor interaction changes sign. In the MnPt phase a simple antiferromagnetic structure occurs with the directions of the magnetic moments dependent on concentration and temperature. There is no direct connection between the anisotropy energy and the lattice dimensions. The MnPt3 phase has simple ferromagnetic structure. The measured transition temperatures are summarized in magnetic phase diagrams. The magnetic structures and transformations of the Mn-Pt system are explained by assuming nearest- and next-nearest-neighbor interactions dependent on the interatomic distances. The magnetic phase diagram of the Mn3Pt phase calculated in the molecular-field approximation is in agreement with the experimental observations.
We present the results of calculations for the equilibrium magnetic behavior of a fcc lattice of U3+(f3, J=(9/2)) ions coupled by the hybridization-mediated two-ion interaction. The calculations are for L-S intraionic coupling, and have been performed both with and without crystal-field interactions being present. We relate our results to the equilibrium magnetic behavior and thermal phase transitions in UP, UAs, and USb.