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Magnetic anisotropy of U{sub 2}Pd{sub 2}In

Description: Magnetic susceptibility studies of the U{sub 2}Pd{sub 2}In single crystal show that in the paramagnetic state larger {chi}-values are found for field along the basal plane than along the c-axis. However, below T{sub N} = 37 K, where U-moments form a non-collinear magnetic structure within the basal plane, a cross-over of the two {chi}-branches occurs. The single crystal results may explain the origin of the exotic magnetization results obtained on powder samples.
Date: September 1, 1995
Creator: Prokes, K.; Nakotte, H. & Havela, L.
Partner: UNT Libraries Government Documents Department

Non-Fermi-liquid scaling in U(Cu,Al){sub 5} compounds

Description: We report on the electronic properties of various UCu{sub x}Al{sub 5-x} compounds (2.9{le}x{le}3.5). These compounds crystallize in the hexagonal CaCu{sub 5} structure. For all compounds, we find that the low-temperature specific heat diverges logarithmitically, which may be taken as an indication of non-Fermi-liquid scaling in these materials. Also we find a large magnetic anisotropy in all compounds studied, and we show that the magnetic anisotropy should not be neglected in the analysis of other bulk properties. Though for some of UCu{sub x}Al{sub 5-x} polycrystals non-Fermi-liquid scaling is found also in the magnetic susceptibility, comparison with single-crystal results on UCu{sub 3}Al{sub 2} indicates that any temperature dependence may be due to averaging anisotropic response over all crystallographic directions.
Date: August 1, 1996
Creator: Nakotte, H.; Buschow, K.H.J.; Brueck, E. & Klaasse, J.C.P.
Partner: UNT Libraries Government Documents Department

GMR in intermetallics

Description: Typical examples of giant magnetoresistance (GMR) effects observed in intermetallic compounds at various conditions are reviewed and some comparisons with the GMR magnetic multilayer systems are shown. Possibilities of tuning material parameters desired for applications are discussed in context of present understanding of the mechanisms responsible for GMR in this class of materials. 18 refs.
Date: April 1, 1996
Creator: Sechowsky, V.; Havela, L.; Nakotte, H. & Brueck, E.
Partner: UNT Libraries Government Documents Department

Electronic properties of U{sub 2}Pt{sub 2}Sn

Description: U{sub 2}Pt{sub 2}Sn is crystallizing in an ordered version (space group P4{sub 2}/mnm) of the tetragonal U{sub 3}Si{sub 2}-type of structure. Clear anomalies in the magnetic susceptibility, specific heat and electrical resistivity around 15 K indicate that U{sub 2}Pt{sub 2}-Sn orders antiferromagnetically below this temperature. As expected for an antiferromagnet, the susceptibility and specific heat anomalies are shifted to lower temperatures upon application of external magnetic field. The specific-heat coefficient {gamma} = 327 mJ/mol f.u. K{sup 2} remains unchanged in fields up to 5T. The antiferromagnetic ground state of U{sub 2}Pt{sub 2}Sn can be concluded also from the metamagnetic transition around 22 T in the magnetization at 4.2 K and from magnetic reflections in the neutron-diffraction pattern at low temperatures.
Date: September 1, 1995
Creator: Prokes, K.; de Boer, F.R. & Nakotte, H.
Partner: UNT Libraries Government Documents Department

Crystallographic and magnetic structure of UCu{sub 1.5}Sn{sub 2}

Description: We report on the crystallographic and magnetic structures of the antiferromagnet UCu{sub 1.5}Sn{sub 2}, as determined by x-ray and neutron powder diffraction. It forms in the tetragonal CaBe{sub 2}Ge{sub 2} structure type, with space group P/4nmm, and we find no site disorder between two different Sn 2c sites, in contrast with a previous report. UCu{sub 1.5}Sn{sub 2} orders antiferromagnetically with a Neel temperature of about 110 K. This is unusually high amongst uranium intermetallics. The uranium moments align along the c-axis in a collinear arrangement but alternating along the c-axis. The low-temperature uranium moment is 1.95{mu}{sub B}.
Date: September 1995
Creator: Purwanto, A.; Robinson, R. A.; Nakotte, H.; Swainson, I. & Torikachvili, M.
Partner: UNT Libraries Government Documents Department

Magnetic phase diagrams of UNiGe

Description: UNiGe undergoes two magnetic transitions in zero field. Here, the magnetic diagrams of UNiGe for B {parallel} b and B {parallel} c are reported. We performed temperatures scans of the magnetization in static magnetic fields up to 19.5T applied along the b and c axes. For both orientations 3 magnetic phases have been identified in the B-T diagrams. We confirmed the previously reported phase boundaries for B {parallel} c, and in addition we determined the location of the phase boundaries for B {parallel} b. We discuss a possible relationship of the two zero-field antiferromagnetic phases (commensurate: T<42K; incommensurate: 42K<T<50K) and the field-induced phase, which, at low temperatures, occurs between 18 and 25T or 4 and 10T for B {parallel} b or B {parallel} c, respectively. Finally, we discuss the field dependence of the electronic contribution {gamma} to the specific heat for B {parallel}c up to 17.5T, and we find that its field dependence is similar to the one found in more itinerant uranium compounds.
Date: November 1, 1997
Creator: Nakotte, H.; Hagmusa, I.H.; Klaasse, J.C.P.; Nakotte, H.; Lacerda, A.H.; Hagmusa, I.H. et al.
Partner: UNT Libraries Government Documents Department

Magnetism in single-crystalline CePtSn.

Description: CePtSn exhibits two antiferromagnetic transitions at low temperatures. We report on magnetoresistance and in magnetization studies of single-crystalline CePtSn in magnetic fields up to 18 T. The data were taken to establish the magnetic phase diagrams for CePtSn in fields applied along the principal directions.
Date: August 4, 1999
Creator: Bordallo, H. N.; Chang, S.; Lacerda, A. H.; Nakotte, H.; Takabatake, T. & Torikachvili, M. S.
Partner: UNT Libraries Government Documents Department

High-field magnetization studies of U{sub 2}T{sub 2}Sn (T=Co, Ir, Pt) compounds

Description: High-field magnetization measurements at 4.2 K on U{sub 2}T{sub 2}Sn (T = Co, Ir and Pt) compounds have been performed on free and fixed powders up to 57 T. An antiferromagnetic ground state of U{sub 2}Pt{sub 2}Sn is corroborated by a metamagnetic transition at 22 T with very small hysteresis going up and down with field. U{sub 2}Co{sub 2}Sn and U{sub 2}Ir{sub 2}Sn show no metamagnetic transition up to 57 T which is in agreement with the non-magnetic ground state of these compounds. In all cases, the maximum applied field is not sufficient to achieve saturation. The short-pulse measurements presented here are compared with previous results obtained in quasi-static fields up to 35 T.
Date: July 1, 1995
Creator: Prokes, K.; Nakotte, H. & de Boer, F.R.
Partner: UNT Libraries Government Documents Department

Effect of pressure on the electrical resistivity and magnetism in UPdSn

Description: The electrical resistivity of a UPdSn single crystal exerted to various hydrostatic pressures was measured as a function of temperature and magnetic field. Clear anomalies in the temperature dependence of resistivity along the c-axis mark the magnetic phase transitions between paramagnetic and antiferromagnetic (AF) state at TN and the AF 1 -AF2 transition at T I .L arge negative magnetoresistance effects have been observed not only in the AF state as a result of the metamagnetic transition to canted structure ai B,, but also at temperatures far above TN. The latter result is attributed to the existence of AF correlations or short range AF ordering in the paramagnetic range. The value of TN increases with increasing applied pressure, whereas TI simultaneously decreases. It is also found that 13, decreases with increasing pressure. As a consequence, the stability range of the AF- 1 phase expands with applied pressure partially on account of the ground-state AF-2 phase.
Date: January 1, 2002
Creator: Honda, F.; Alsmadi, A. K. (Abdel Khaleq); Sechovsky, V. (Vladimir); Kamarad, J.; Nakotte, H. (Heinrich); Lacerda, A. H. (Alex H.) et al.
Partner: UNT Libraries Government Documents Department

Antiferromagnetic order in uranium nickel(0.39) rhodium (0.61) aluminum.

Description: As the archetype magnetic intermetallic compounds IJNiAI (antiferromagnet, TN = 19K) and URhAI (ferromagnet, TC = 27K) [1] ., iJNi0.39Rh0.61A1 crystallizes in the hexagonal ZrNiAI-type structure . UNi0 .39Rh0.61A1 undergoes antiferromagnetic (AF) at TN = 13K . Here, we report on resistance and magnetoresistance studies on single-crystalline UNi0 .39Rh0.61A1 in magnetic field up to 18T applied along and perpendicular to the c-axis. 20-Tesla National High Magnetic Field Laboratory (NHMFL) at Los Alamos has been used to investigate such magnetic properties . This compound is found to exhibit highly anisotropic properties with the easy magnetization axis along the c-axis . While for fields applied along c-axis, 3T completely suppresses the AF ordering, antiferromagnetism persists up to the highest field of 18T applied perpendicular to the c-axis, see Fig.(1) which shows R(ohm) vs B (T) . The results are discussed in terms of variation of the 5f-ligand hybridization compared to the one of its parent compounds.
Date: January 1, 2003
Creator: El-Khatib, S.; Alsmadi, A. K. (Abdel Khaleq); Nakotte, H. (Heinrich); Andreev, A.V. (A.V.) & Lacerda, A. H. (Alex H.)
Partner: UNT Libraries Government Documents Department

Nonmagnetic crystal-electric-field ground state in the heavy-fermion compound PrInAg{sub 2}

Description: The authors have performed inelastic neutron scattering measurements that confirm that the crystal-electric-field split ground state in the heavy-fermion compound PrInAg{sub 2} is a nonmagnetic, non-Kramers doublet. This implies that a quadrupolar Kondo interaction is responsible for the enhanced thermodynamic properties observed at low temperatures. They also observe anomalous broadening of the inelastic peaks and suggest two possible causes for this broadening.
Date: June 18, 1998
Creator: Kelley, T.M.; Beyermann, W.P.; Robinson, R.A.; Nakotte, H.; Canfield, P.C. & Trouw, F.
Partner: UNT Libraries Government Documents Department

Effects of hydrogen absorption in TbNiAl and UNiAl

Description: Although hydrides of intermetallic compounds are used extensively as hydrogen-storage media, little is known about the exact nature of metal-hydrogen interactions. However, this knowledge is of essential importance for the understanding of thermodynamics and other properties. Hydrides (deuterides) of TbNiAl and UNiAl have been widely studied because of drastic increase of magnetic ordering temperature under hydrogenation. Here the authors report neutron-diffraction results of the three deuterides, TbNiAlD{sub 1.28}, TbNiAlD{sub 0.8}a nd UNiAlD{sub 2.23}.
Date: December 31, 1998
Creator: Bordallo, H.N.; Nakotte, H.; Schultz, A.; Kolomiets, A.V.; Havela, L. & Andreev, A.V.
Partner: UNT Libraries Government Documents Department

Low-energy excitations, symmetry breaking and specific heat in YbBiPt

Description: The heavy fermion compound YbBiPt has a very large linear coefficient of specific heat {gamma} = 8 Jmol{sup {minus}1} K{sup {minus}2} and this is understood, to first order, in terms of the observed low-energy neutron scattering response. However, at low temperatures, symmetry forbidden splittings at 1 and 2 meV respectively are observed. These levels give good qualitative agreement with the measured specific heat, but poor quantitative agreement. Indeed, the specific heat drops more rapidly with temperature that can be accounted for assuming a temperature-independent density of states. The authors also present new low-temperature crystallographic data, which rule out any significant structural distortions.
Date: December 31, 1998
Creator: Robinson, R.A.; Christianson, A.; Nakotte, H.; Beyermann, W.P. & Canfield, P.C.
Partner: UNT Libraries Government Documents Department

Thermal properties of UPdSn and UCuSn

Description: The authors report on the specific-heat and the thermopower of UPdSn and UCuSn, both of which order antiferromagnetically at low temperatures. Both compounds show similar behavior in the specific heat, and the large magnetic-entropy changes around T{sub N} are evidence for a large degree of 5f-electron localizations. The thermopower, on the other hand, behaves very different in the two compounds. While prominent features are seen in the temperature dependence of the thermopower of UCuSn, only weak changes are observed for UPdSn. This may indicate that, for these compounds, the thermopower response is due to mechanisms other than purely magnetic ones.
Date: September 1, 1996
Creator: Kawanaka, H.; Nakotte, H.; Brueck, E.; Prokes, K.; Kim-Ngan, N.H.; Takabatake, T. et al.
Partner: UNT Libraries Government Documents Department

Short range spin correlations in the CMR material La{sub 1.41}Sr{sub 1.6}Mn{sub 2}O{sub 7}

Description: The (La{sub 1{minus}x}Sr{sub x}){sub 2}Mn{sub 3}O{sub 7} compounds are layered materials that exhibit higher magneto-resistance than the corresponding 3D manganite perovskites. Quasi-elastic neutron scattering on a polycrystalline sample of La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} shows that the spin fluctuation spectrum of these layered CMR materials is qualitatively similar to those found in the perovskite manganites (La,Ca)MnO{sub 3}; their concentration, lifetime, and coherence length increase as T decreases to {Tc}. Unlike the perovskites the authors found a lower spin-diffusion constant above {Tc} of {approximately} 5 meV {angstrom}{sup 2}.
Date: December 1, 1997
Creator: Kelley, T.M.; Argyriou, D.N.; Robinson, R.A.; Nakotte, H.; Mitchell, J.F.; Osborn, R. et al.
Partner: UNT Libraries Government Documents Department

Magnetic phase diagram of Tb{sub 3}Co

Description: The orthorhombic Tb{sub 3}Co compound exhibits both ferromagnetic and antiferromagnetic behavior below the critical temperature T{sub t} = 72 K as evidenced by metamagnetic transitions along the a- and b-axes and ferromagnetic magnetization process along the c-axis. In the temperature interval between T{sub t} and the Neel temperature T{sub N} = 82 field-induced transitions along all three axes are observed. This behavior results from the complex noncomplanar magnetic structure of Tb{sub 3}Co. The metamagnetic transitions are accompanied by a significant magnetoresistance effect. The Tb{sub 3}Co single crystal has permanent magnet properties along the c-axis with the highest energy up to 140 Mg Oe at T < 4.2 K.
Date: August 1, 1997
Creator: Baranov, N.V.; Markin, P.E.; Nakotte, H. & Lacerda, A.
Partner: UNT Libraries Government Documents Department

Localized excitations in UPdSn

Description: The authors have measured the inelastic neutron-scattering response of UPdSn at various temperatures using the HET and PHAROS spectrometers at the ISIS and MLNSC facilities, respectively. UPdSn shows some quasielastic scattering, which may be attributed to the hybridization of the 5f electrons with the conduction electrons. Furthermore, they find a clear excitation around 40meV above 40K in addition to the phonon contribution. While this excitation may be indicative of crystal fields in UPdSn, its strong temperature dependence seems to contradict a simple crystal-field picture. Below T{sub N}, the unusual temperature dependence may be attributed to magnetically-driven distortions (and subsequent changes in the local surrounding of the U ions), but there is some evidence that other additional mechanism(s) may contribute above T{sub N}. Some possible mechanisms will be discussed.
Date: November 1, 1997
Creator: Nakotte, H.; Robinson, R.A.; Swan, T.; Kelley, T.; Bull, M.; McEwen, K.A. et al.
Partner: UNT Libraries Government Documents Department

Structural and magnetic properties of UCo{sub 1/3}T{sub 2/3}Al solid solutions (T = Ru, Pt, Rh).

Description: We report on neutron diffraction studies of UCo{sub 1/3}T{sub 2/3}Al (T = Ru, Pt, Rh). All three solid solutions form in the hexagonal ZrNiAl structure. The Ru-containing compound is found to be chemically ordered, while the Pt-containing compound is nearly disordered and the Rh-containing compound is purely disordered. All three compounds exhibit long-range magnetic order with rather small U moments.
Date: August 6, 1999
Creator: Andreev, A. V.; Bordallo, H. N.; Chang, S.; Nakotte, H.; Schultz, A. J.; Sechovsky, V. et al.
Partner: UNT Libraries Government Documents Department

Electronic properties of UCuSn

Description: Crystallographic analysis shows that UCuSn does not form in the hexagonal CaIn{sub 2} structure as reported previously, but is an ordered ternary compound and forms in an orthorhombic structure. Bulk and neutron-diffraction measurements reveal that UCuSn orders antiferromagnetically below 60 K. At 4.2 K, high-field magnetization reveal a complex magnetization process with two metamagnetic transitions. Furthermore, bulk investigations show an additional anomaly at 25 K, but a regular temperature dependence of various magnetic peaks down to the lowest temperature gives no evidence for a second magnetic transition. Possible scenarios responsible for the drastic changes in the electronic properties around 25 K are discussed.
Date: September 1, 1995
Creator: Nakotte, H.; Purwanto, A.; Robinson, R.A.; Prokes, K.; Boer, F.R. de; Havela, L. et al.
Partner: UNT Libraries Government Documents Department

Magnetic properties and crystal structure of RENiA1 and UniA1 hydrides.

Description: RENiAl (RE = rare-earth metal) and UNiAl compounds crystallizing in the hexagonal ZrNiAl-type structure (space group P{bar 6}2m) can absorb up to 2 and 3 hydrogen (deuterium) atoms per formula unit, respectively. Hydrogenation leads to a notable lattice expansion and modification of magnetic properties. However, the impact of hydrogenation on magnetism is the opposite for 4f- and 5f-materials: TN(T{sub c})is lowered in the case of rare-earth hydrides, while for UNiAlH(D){sub x} it increases by an order of magnitude. Here we present results of magnetic and structure studies performed of these compounds, focusing on the correlation between magnetic and structural variations and discussing possible reasons of the striking difference in effect of hydrogenation on rare-earth and actinide intermetallics.
Date: August 11, 1999
Creator: Bordallo, H. N.; Drulis, H.; Havela, L.; Iwasieczko, W.; Kolomiets, A. V.; Nakotte, H. et al.
Partner: UNT Libraries Government Documents Department

Magnetic and crystallographic structures in UTX intermetallic compounds

Description: Uranium, along with other actinides and lanthanides, forms a large group of ternary intermetallic compounds of stoichiometry UTX (T = transition metal, X = p-electron metal). These compounds are formed in several structure types and the occurrence and stability of particular structures with respect to the transition metal content suggests reasonable systematics. The authors have also investigated the magnetic structures of selected UTX compounds and it is revealing to relate the crystallographic and magnetic structures, because of the relationship between the magnetic symmetry and that of the U-atom environment produced by the 5f-ligand hybridization, and the consequent anisotropic exchange. Those of ZrNiAl structure type are collinear, with moments along the hexagonal c-axis. In the orthorhombic NiSiTi structure type, the moments are confined to the b- c plane (perpendicular to the uranium chains) and the structures are often incommensurate. In the hexagonal CaIn{sub 2} (or GaGeLi) structure type, the magnetic structures form in an orthorhombic cell, and at least in the disordered centric group, again the moments lie perpendicular to the nearest-neighbor uranium spacing. This work presents a phenomenology of trends in UTX ternary compounds. It is shown that there is an apparent strong hybridization parallel to nearest neighbor U-U directions, with ferromagnetic coupling in the same directions. There may be a systematic relationship between the hybridization anisotropy and the magnetic anisotropy, in which the quantization axes are the same and the moments point along directions of relatively weak hybridization.
Date: August 1, 1993
Creator: Robinson, R. A.; Lawson, A. C.; Sechovsky, V.; Havela, L.; Kergadallan, Y.; Nakotte, H. et al.
Partner: UNT Libraries Government Documents Department