High-resolution neutron diffraction study of the U1-xNdxCo2Ge2 (x = 0.25) compound shows a separation into two phases, each order antiferromagnetically at a different temperature. The temperature dependence of the magnetic moment is deduced for both phases. The results are in agreement with previous low-resolution neutron diffraction measurements, (C) 2000 Elsevier Science B.V. All rights reserved.

The individual sizes and orientations of the magnetic moments of Tb and Co in different sites were studied by neutron diffraction of Tbn+1Co3n+5B2n (n=1, 2, 3, and ∞). Total magnetic moments obtained by our neutron diffraction measurements are in agreement with the literature and our superconducting quantum interference device measurements. The local atomic volumes dependence of Tb and Co magnetic moments are discussed using the Wigner–Seitz cell construction method.

Neutron diffraction, AC-susceptibility, and SQUID magnetization study of (Nd1−xTbx)Co2Ge2 solid solutions is summarized in the form of a tentative magnetic phase diagram. The magnetic ordering of the (Nd1−xTbx)Co2Ge2 system is compared to the (Nd1−xUx)Co2Ge2 system. The U effect on the magnetic structures is found to be more dominant than that of Tb on Nd.

UNi2Si2 orders magnetically at 124±1 K in an incommensurate (IC) phase, undergoes transition at 103±1 K to AF-I (+−+−) phase, and then another transition at 53±1 K to a ferrimagnetic (++−) phase. A.c.-susceptibility and neutron-diffraction studies of polycrystalline U(Ni,M)2Si2 solid solutions, with minor M=Co and Cu (U(Co1−yNiy)2Si2 with y=0.75, 0.90, and 0.95, and U(Ni1−zCuz)2Si2, with z=0.05, 0.10, and 0.25) confirm an IC phase for y=0.90 below 119±2 K down to 105±2 K and suggest (by a.c.-susceptibility only) IC phases below TN for compositions between y≈0.85 and z≈0.05. The above ferrimagnetic phase is observed at T≤12 K also for compositions between y≈0.93 and z≈0.03. The magnetic phase diagram in the vicinity of UNi2Si2 is redrawn and discussed.

Neutron-diffraction measurements on TbCo3B2, with the isotope B11, show ferromagnetic structure below 35(2) K. Ordered magnetic moments of Tb and Co were found to be in the basal planes directed parallel to each other. The Tb ordered moment is significantly smaller than its free-ion value. The Co ordered moment is nearly zero. Ac-susceptibility and SQUID magnetometer measurements agree with the neutron results.

Solid solutions of the $({\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}){\mathrm{Co}}_{2}{\mathrm{Ge}}_{2}$ system ($x=0.25,$ 0.50, 0.75) are found by neutron diffraction to have tetragonal ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type crystal structure (space group $I4/mmm$), same as their end compounds ($x$ $=0,$ 1). In the solid solutions, U and Nd atoms are randomly distributed in the basal planes. The end compounds and the solid solutions are paramagnetic at room temperature. At 12 K the (U,Nd) sublattice has the antiferromagnetic AF-I magnetic structure [+-+- stacking of ferromagnetic (U,Nd) planes along $c$], with moments parallel to the $c$ axis. It is found that within a ferromagnetic basal plane the U magnetic moments are parallel to the Nd magnetic moments, unlike (U,Tb), where they are antiparallel. This shows that the ``spin charge'' rule for lanthanides extends to U-lanthanide systems. Neutron-diffraction and ac-susceptibility results are compared in order to investigate the character of the magnetic transition in the solid solutions.

Using neutron diffraction, a second stage physintercalation of molecular N(2) into C(24)Rb has been observed in which the N(2) molecules reside inside every second Rb layer. The new phase, C(48)Rb(2)(N(2))(x), coexists below 175 K with pure C(24)Rb and the 1st stage C(24)Rb(N(2))(x). The tilt of the N(2) molecular axes relative to the graphene planes was determined versus T using the nuclear resonance photon scattering (NRPS) technique and found to be almost parallel to the graphene planes of the C(24)Rb sample.

Solid solutions of the $({\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}){\mathrm{Co}}_{2}{\mathrm{Ge}}_{2}$ system ($x=0.25,$ 0.50, 0.75) are found by neutron diffraction to have tetragonal ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type crystal structure (space group $I4/mmm$), same as their end compounds ($x$ $=0,$ 1). In the solid solutions, U and Nd atoms are randomly distributed in the basal planes. The end compounds and the solid solutions are paramagnetic at room temperature. At 12 K the (U,Nd) sublattice has the antiferromagnetic AF-I magnetic structure [+-+- stacking of ferromagnetic (U,Nd) planes along $c$], with moments parallel to the $c$ axis. It is found that within a ferromagnetic basal plane the U magnetic moments are parallel to the Nd magnetic moments, unlike (U,Tb), where they are antiparallel. This shows that the ``spin charge'' rule for lanthanides extends to U-lanthanide systems. Neutron-diffraction and ac-susceptibility results are compared in order to investigate the character of the magnetic transition in the solid solutions.

The pressure effect on the magnetic and crystallographic structures of the materials UCu2Ge2, and U(Ni0.05Cu0.95)2Ge2 are studied by neutron diffraction in the applied pressure range of ambient to 0.63 GPa, at room temperature and 60 K. The compressibilities of the materials are found to be isotropic, and very similar for both materials and temperatures. This isotropy is explained by a free-electron gas control of the compressibility. No pressure effect on the magnetic structures or on the magnitude of the magnetic moments was observed for both materials. This result is discussed in the framework of the RKKY model.

A neutron-diffraction study of U(Co1− yNiy)2Si2 and U(Ni1 − zCuz)2Si2 solid solutions in the vicinity of UNi2Si2 shows that the ferrimagnetic (+ + −) phase with k = (0, 0, 2/3) of the latter is observed also for materials with y = 0.95 and z = 0.05, below the AF-I phase with k = (0, 0, 1). This ferrimagnetism exists below 50 ± 4K in U(Co0.05Ni0.95)2Si2, with U moment of 1.75 ± 0.11 μB at 12 K, and coexists with an AF-I phase below 37 ± 5K in U(Ni0.95Cu0.05)2Si2, with U moment of 1.79 ± 0.15 μB at 12 K. The ferrimagnetic phase extends between y ≈ 0.93 and z ≈ 0.03. Its abrupt appearance upon a minor change in conduction-electron concentration is attributed to RKKY-like interactions.

Solid solutions of the (U1-xNdx)Co2Ge2 system (x = 0.25, 0.50, 0.75) are found by neutron diffraction to have tetragonal ThCr2Si2-type crystal structure (space group I4/mmm), same as their end compounds (x = 0, 1). In the solid solutions, U and Nd atoms are randomly distributed in the basal planes. The end compounds and the solid solutions are paramagnetic at room temperature; At 12 K the (U,Nd) sublattice has the antiferromagnetic AF-I magnetic structure [+ - + - stacking of ferromagnetic (U,Nd) planes along c], with moments parallel to the c axis. It is found that within a ferromagnetic basal plane the U magnetic moments are parallel to the Nd magnetic moments, unlike (U,Tb), where they are antiparallel. This shows that the "spin charge" rule for lanthanides extends to U-lanthanide systems. Neutron-diffraction and ac-susceptibility results are compared in order to investigate the character of the magnetic transition in the solid solutions.

Magnetic interactions in some intermetallic AM2X2 compounds and their solid solutions have been investigated using ac-susceptibility and neutron-diffraction measurements. The materials studied (A = U, Nd, Tb; M = Co, Ni, Cu; X = Si, Ge) have predominantly the tetragonal ThCr2Si2-type crystal structure, and ordered magnetic moments are found only on the A site aligned along the tetragonal axis in ferromagnetic basal planes. The magnetic phase diagrams of the U(M,M')2X2 solid solutions have been determined. The results suggest RKKY-like magnetic interactions in these systems, with variable magnetic structure and oscillatory behaviour of the ordering and paramagnetic Curie temperatures. The relative orientation of ordered A and Ln magnetic moments in the (A,Ln)Co2Ge2 solid solutions have been determined. It is antiparallel for the (U,Tb) and (Nd,Tb) cases and parallel for the (U,Nd) case, in accordance with the "spin-charge" concept.

The relative orientation of ordered magnetic moments of f-atoms (A,A′) occupying randomly the same site, has been studied by powder neutron diffraction in the magnetically-ordered state of (A,A′)Co2Ge2 solid solutions. These materials crystallize in the ThCr2Si2-type structure and order antiferromagnetically in the AF-I structure, characterized by ferromagnetic (A,A′) basal planes stacked alternately (+−+−) along the tetragonal axis, with A and A′ moments aligned along this axis. The `spin-charge' concept, which accounts for antiparallel orientation of light and heavy lanthanide moments in (Nd1−xTbx)Co2Ge2, is found to apply also to uranium and terbium moments in (U1−xTbx)Co2Ge2. The parallel orientation of uranium and neodymium moments, observed in (U1−xNdx)Co2Ge2, also follows the `spin-charge' concept. Uranium and terbium moment compensation (in basal planes of zero total moment) is anticipated for a (U1−xTbx)Co2Ge2 solid solution with x≈0.15.

The relative orientation of magnetic moments of uranium (5f-atom) and a lanthanide (Ln, 4f-atom), occupying randomly the same site, was investigated by neutron diffraction in the ordered state of the systems (U1 − xLnx)Co2Ge2 with light (LnNd) and heavy (LnTb) lanthanide. These materials crystallize in the ThCr2Si2-type structure. Most of them order in the antiferromagnetic AF-I structure, with alternate (+ −) stacking of (U, Ln) planes having net moment, and f-moments along the tetragonal axis. It is found that the U and Nd moments in (U1 − xNdx)Co2Ge2 are parallel, while the U and Tb moments in (U1 − xTbx)Co2Ge2 are antiparallel. This is apparently due to in-plane direct exchange between f-atoms, in agreement with the “spin-charge” concept, considering that the U moments behave like light Ln.

The relative orientation of magnetic 4f-moments of neodymium and terbium, randomly occupying the same site, was investigated by neutron diffraction in the ordered magnetic state of the solid solutions (Nd 1− x Tb x )Co 2 Ge 2 (ThCr 2 Si 2 -type crystal structure). The antiparallel magnetic ordering observed confirms the “spin-charge” concept for lanthanides.

Powder neutron diffraction of Zr(AlxFe1−x)2 intermetallics (x=0–1) has been performed at room temperature in an attempt to study the variation of their bonding properties as a function of x. The Debye–Waller factors indicate a minimum of the bonding strength for both the Zr and the Fe/Al sites in the Zr(AlxFe1−x)2 compounds at x=0.2. A similar minimum has also been observed by other experimental techniques, and it corresponds to the maximum hydrogen absorption in the above intermetallic system.

Upon cooling a single-phase sample of C24Rb under N-2 pressure, intercalation of N-2 into C24Rb starts immediately below RT. A single phase of C24Rb(N-2)(x) is formed, where N-2 resides at every Rb layer, and x increases monotonically as temperature decreases. In the temperature range 175 > T > 140K a phase transition occurs, and for T less than or equal to 140K three phases co-exist: C24Rb,C24Rb(N-2)(x) and C48Rb2(N-2)(x). The third phase, has a stacking where N-2 resides at every second Rb layer, hence, it is second stage compound in the intercalation of N-2 in C24Rb.