We report on the magnetic behaviour of Npln(3) as inferred from single crystal magnetization and neutron diffraction measurements and from powder Np-237 and Sn-119 Mossbauer data. Magnetization curves reveal a 'ferromagnetic' like order below 14 K, [1 1 1] being the easy axis, and the presence of two distinct magnetic phases at lower temperatures. Mossbauer and neutron diffraction data point towards the existence of a modulated AF phase below 9 K. However, a simple ferromagnetic order at 10 K < T < 14 K seems to be excluded from the Mossbauer experiments.

Neutron-scattering and specific-heat measurements of the heavy-fermion superconductor URu2Si2 under hydrostatic pressure and with Rh-doping, U(Ru0.98Rh0.02)(2)Si-2, show the existence of two magnetic phase transitions. At T-m similar to 17.5 K, a second-order phase transition with strong anomalies in the specific heat and other macroscopic and transport properties are accompanied by an antiferromagnetically ordered dipolar moment of only 0.03 mu(B). At T-M < T-m under pressure, p >= 5 kbar, or small Rh doping, a first-order phase transition gives rise to small anomalies in the specific heat and a large ordered moment of similar to 0.3 mu(B), but with the same magnetic structure. The results can be understood in terms of a hidden order parameter psi, which is linearly coupled to the ordered moment m. It follows that m and psi have the same symmetry and hence both break time-reversal symmetry. (c) 2005 Elsevier B.V. All rights reserved.

Results of polarized neutron diffraction on the compound CeB6 are used to obtain its magnetization density distribution. The measurements are performed at two different points of the magnetic phase diagram (phase I and II). The data are analysed in direct space using the maximum entropy method, as well as in reciprocal space using the cerium form factor expansion and anisotropy. The conclusion is that, in both phases, the magnetization is localized on the cerium sites only. This result is in contradiction to a recent paper by Saitoh et al (2002 J. Phys. Soc. Japan 71 2369), claiming that, in phase II, a localized spin moment was observed at non-atomic sites.

DyIn3 orders at T-N = 20 K and undergoes a second spontaneous magnetic transition at 16.5 K. From bulk magnetization measurements, performed on a single crystal along the three main axes of the cubic AuCu3-type structure, the magnetic phase diagrams have been established. The crystalline electric field (CEF) scheme, in the paramagnetic phase, and the magnetic structures of the spontaneous and low field-induced phases have been probed by neutron techniques. All the magnetic phases studied are found to be multiple q with q belonging to the (1/2, 1/2, 0) star. In the low temperature phase (T < 16.5 K) the structure is double q with moments along twofold axes, whereas above 16.5 K it becomes triple q with moments along threefold axes. The analysis of the experimental results within the periodic molecular field model leads to a coherent interpretation of the spontaneous magnetic transitions, mainly driven by bilinear exchange and CEF interactions. Though the existence of quadrupolar interactions is definitively proved by the stabilization of multiple q magnetic structures, quadrupolar coefficients are found to be one order of magnitude smaller than those previously reported for NdIn3 and TbIn3.

Spin correlation in Cu–O chains of YBCO are studied. The results were obtained at T=110 K by neutron polarization analysis with 3He filter as analzyer. Experimental data indicate a magnetic peak at k=0.75, which corresponds to the holes concentration in the chain c=0.5. There is another anomaly at k=0.5 (c=0), which may be connected with the sample inhomogenity and some admixtures of copper oxide. The cross-section in the peak at k=0.75 is 5 mb/sr.

Single-crystalline sample of UNiAl which orders antiferromagnetically below T-N = 19.3 K in a complex way (q = (0.1, 0.1 0.5)) has been investigated by neutron diffraction under pressure up to 4.9kbar. Although electrical resistivity measurements reveal a drastic changed of the low-temperature transport properties around 3 kbar suggesting a change of the magnetic-structure propagation we have not found any indication for such a change. As the pressure increases, U magneticmoment magnitudes decrease slightly and the magnetic structure gets less perfect. However, the antiferromaganetic structure of UNiAl remains stable in the whole temperature and pressure range studied. (C) 2001 Elsevier Science BY. All rights reserved.

A number of magnetic and structural phase transitions in EuMn2O5 is observed below TN ≃ 40K by neutron diffraction on a single crystal. The magnetic structure just below TN is incommensurate with the propagation vector (1200.3). A ferroelectric transition occurs at TN with the polar displacements of Mn3+ ions along axis a. Three-dimensional polarization analysis has shown, that magnetic moments lie in a–c plane down to T1≃ 22K. Second structural transition, mainly due to the polar shifts of the Mn4+ ions along c, is observed at T1. It is accompanied by a magnetic phase transition and by appearance of the b-component of spins.

The magnetic structure of nonstoichiometric LuFe4+deltaAl8-delta and YFe4+deltaAl8-delta compounds with a small Fe excess (delta similar to0.40) was investigated by Mossbauer spectroscopy, magnetization measurements, and both polarized and unpolarized neutron-scattering experiments on single crystals. The small excess of Fe atoms substitute Al at the 8j positions and have a pronounced effect on the magnetic properties. The Neel temperature decreases from similar to 190 to 100 K and the magnetic ordering changes from the cycloid modulation found in the stoichiometric compounds to an amplitude modulated wave with a much shorter period.

A number of superstructure reflections (h/2k/2l/2) with h,k,l=2n+1 are observed in the intermediate phase II of CeB6 by resonant X-ray scattering at the LII and LIII absorption edges of Ce. This gives evidence of a zero-field ordering with wave vector k0=2π/a[1/21/21/2]. The intensities of the reflections (5/21/21/2), (5/23/23/2) and (7/21/21/2) in nonresonant conditions, where reliable calculations can be made, are consistent neither with the Jahn–Teller pair distortion nor with the Γ3 quadrupolar ordering proposed in the literature as possible zero-field ordering mechanisms. Apparently, the Γ5 quadrupolar ordering accompanied by displacements of the boron atoms should also be considered, but the experimental data do not allow to draw definite conclusions.

Itinerant magnets with large orbital moments are uncommon. We show that UGa3 is such a material where the itinerant magnetism is carried by the 5f states. The definitive evidence comes from neutron diffraction measurements of the magnetization distribution, where a significant difference is observed in the momentum dependence of the scattering amplitude above and below TN. The change in the magnetization distribution when the antiferromagnetic order appears is due to the antiparallel coupling of large atomic 5f spin and orbital moments below TN, whereas above TN there is spin degeneracy and no disordered local moments.

In the UxLa1-xS system there is an abrupt loss of the long-range ferromagnetic ordering found in pure US at a critical concentration x c ∼ 0.57, which is far above the percolation limit. As the magnetic ground state in such a system can be strongly affected by small variations of the 5f localization, we have investigated a set of samples with different x by polarized neutron diffraction and X-ray magnetic circular dichroism (XMCD). The neutron results are consistent with early measurements performed on pure US. Even at the lowest U content (x = 0.15, below x c ) the shape of the induced form factor (f (Q)) is comparable with that found for x = 1 and is well reproduced by either a U4+ or a U3+ state. The ratio between the orbital and the effective spin moments in the XMCD measurements confirms this result, but the evolution of the shape at the M5 edge suggests an abrupt change in the distribution of the electrons (holes) in the 5f density of states around x c .

Neutron diffraction and magnetization measurements of the diluted crystal Fe1−xMgxBr2 (x∼0.15) were performed. Successive phase transitions at zero applied field at TN1∼12 K and TN2∼10 K were found. A transverse ferromagnetic moment was detected just below TN2.

A number of superstructure reflections (h/2 k/2 l/2) with h, k, l = 2n + 1 are observed in the intermediate phase II of CeB6 by resonant X-ray scattering at the L-II and L-III absorption edges of Ce. This gives evidence of a zero-field ordering with wave vector k(0) = 2 pi /a [1/2 1/2 1/2]. The intensities of the reflections (5/2 1/2 1/2), (5/2 3/2 3/2) and (7/2 1/2 1/2) in nonresonant conditions, where reliable calculations can be made, are consistent neither with the Jahn-Teller pair distortion nor with the Gamma (3) quadrupolar ordering proposed in the literature as possible zero-field ordering mechanisms. Apparently, the rs quadrupolar ordering accompanied by displacements of the boron atoms should also be considered, but the experimental data do not allow to draw definite conclusions. (C) 2001 Elsevier Science B.V. All rights reserved.

The magnetic structure of nonstoichiometric ${\mathrm{LuFe}}_{4+\ensuremath{\delta}}{\mathrm{Al}}_{8\ensuremath{-}\ensuremath{\delta}}$ and ${\mathrm{YFe}}_{4+\ensuremath{\delta}}{\mathrm{Al}}_{8\ensuremath{-}\ensuremath{\delta}}$ compounds with a small Fe excess $(\ensuremath{\delta}\ensuremath{\sim}0.40)$ was investigated by M\"ossbauer spectroscopy, magnetization measurements, and both polarized and unpolarized neutron-scattering experiments on single crystals. The small excess of Fe atoms substitute Al at the $8j$ positions and have a pronounced effect on the magnetic properties. The N\'eel temperature decreases from \ensuremath{\sim}190 to 100 K and the magnetic ordering changes from the cycloid modulation found in the stoichiometric compounds to an amplitude modulated wave with a much shorter period.

The magnetic structure of HoBe13 and its evolution under an applied magnetic field have been examined using neutron diffraction and bulk magnetization measurements on a single crystal. In the absence of an external field this cubic compound orders at T-N = 5.7(1)K into a regular helical magnetic structure with propagation vector k = [001/3]. Third order harmonics appear at 4.4(1) K and are attributed to a deformation of the helical structure below this temperature. When a magnetic field is applied along a [001] axis two magnetic transitions occur. First the magnetic domain with propagation vector parallel to the field is favored and, with the addition of the induced ferromagnetic component, by about 4 kG we have a single-domain conical structure, The surprising observation was that at higher fields (15 kG at 1.4 K) the other two domains reappear and become the preferred ones. This reentrant behavior is due to the change of the magnetic structure to a canted arrangement, involving a ferromagnetic component along the applied field and a transverse collinear antiferromagnetic component. When the magnetic field is applied along a [110] axis only one transition is observed from the helical to the conical structure. The magnetic phase diagram of HoBe13 has been constructed.