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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Evolution of short-range magnetic correlations in ferromagnetic Ni-V alloys

Here we experimentally study how the magnetic correlations develop in a binary alloy close to the ferromagnetic quantum critical point with small-angle neutron scattering (SANS). Upon alloying the itinerant ferromagnet nickel with vanadium, the ferromagnetic order is continuously suppressed. The critical temperature T c vanishes when vanadium concentrations reach the critical value of x c =0.116 indicating a quantum critical point separating the ferromagnetic and paramagnetic phases. Earlier magnetization and μ⁢SR data have indicated the presence of magnetic inhomogeneities in Ni 1-x ⁢V x and, in particular, recognize the magnetic clusters close to x c , on the paramagnetic and on the ferromagnetic sides with nontrivial dynamical properties [R. Wang et al., Phys. Rev. Lett. 118, 267202 (2017)]. We present the results of SANS study with full polarization analysis of polycrystalline Ni 1-x⁢ V x samples with x=0.10 and x=0.11 with low critical temperatures T c <50 K. For both Ni-V samples close to x c we find isotropic magnetic short-range correlations on the nanometer scale persisting at low temperatures. They are suppressed gradually in higher magnetic fields. In addition, signatures of long-range ordered magnetic domains are present below T c . The fraction of these magnetic clusters embedded in the ferromagnetic ordered phase grows toward x c and agrees well with the cluster fraction estimate from the magnetization and μ⁢SR data. Our SANS studies provide new insights into the nature of the inhomogeneities in a ferromagnetic alloy close to a quantum critical point.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Containerless processing of undercooled melts

The investigation focused on the control of microstructural evolution in Mn-Al, Fe-Ni, Ni-V, and Au-Pb-Sb alloys through the high undercooling levels provided by containerless processing, and provided fundamental new information on the control of nucleation. Solidification analysis was conducted by means of thermal analysis, x-ray diffraction, and metallographic characterization on samples processed in a laboratory scale drop tube system. The Mn-Al alloy system offers a useful model system with the capability of phase separation on an individual particle basis, thus permitting a more complete understanding of the operative kinetics and the key containerless processing variables. This system provided the opportunity of analyzing the nucleation rate as a function of processing conditions and allowed for the quantitative assessment of the relevant processing parameters. These factors are essential in the development of a containerless processing model which has a predictive capability. Similarly, Ni-V is a model system that was used to study duplex partitionless solidification, which is a structure possible only in high under cooling solidification processes. Nucleation kinetics for the competing bcc and fcc phases were studied to determine how this structure can develop and the conditions under which it may occur. The Fe-Ni alloy system was studied to identify microstructural transitions with controlled variations in sample size and composition during containerless solidification. This work was forwarded to develop a microstructure map which delineates regimes of structural evolution and provides a unified analysis of experimental observations. The Au-Pb-Sb system was investigated to characterize the thermodynamic properties of the undercooled liquid phase and to characterize the glass transition under a variety of processing conditions. By analyzing key containerless processing parameters in a ground based drop tube study, a carefully designed flight experiment may be planned to utilize the extended duration microgravity conditions of orbiting spacecraft.

Perepezko, J. H.↗
DOE OSTI2020

Materials Data on VNi2 by Materials Project

Ni2V crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. V is bonded to two equivalent V and ten equivalent Ni atoms to form VV2Ni10 cuboctahedra that share corners with two equivalent VV2Ni10 cuboctahedra, corners with ten equivalent NiV5Ni7 cuboctahedra, edges with twelve equivalent VV2Ni10 cuboctahedra, edges with twelve equivalent NiV5Ni7 cuboctahedra, faces with four equivalent VV2Ni10 cuboctahedra, and faces with fourteen equivalent NiV5Ni7 cuboctahedra. Both V–V bond lengths are 2.52 Å. There are two shorter (2.52 Å) and eight longer (2.53 Å) V–Ni bond lengths. Ni is bonded to five equivalent V and seven equivalent Ni atoms to form NiV5Ni7 cuboctahedra that share corners with five equivalent VV2Ni10 cuboctahedra, corners with seven equivalent NiV5Ni7 cuboctahedra, edges with six equivalent VV2Ni10 cuboctahedra, edges with eighteen equivalent NiV5Ni7 cuboctahedra, faces with seven equivalent VV2Ni10 cuboctahedra, and faces with eleven equivalent NiV5Ni7 cuboctahedra. There are six shorter (2.52 Å) and one longer (2.55 Å) Ni–Ni bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VNi3 by Materials Project

Ni3V is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. V is bonded to twelve Ni atoms to form VNi12 cuboctahedra that share corners with four equivalent VNi12 cuboctahedra, corners with eight equivalent NiV4Ni8 cuboctahedra, edges with eight equivalent VNi12 cuboctahedra, edges with sixteen equivalent NiV4Ni8 cuboctahedra, faces with four equivalent VNi12 cuboctahedra, and faces with fourteen NiV4Ni8 cuboctahedra. There are four shorter (2.49 Å) and eight longer (2.52 Å) V–Ni bond lengths. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded to four equivalent V and eight Ni atoms to form NiV4Ni8 cuboctahedra that share corners with twelve equivalent NiV4Ni8 cuboctahedra, edges with eight equivalent VNi12 cuboctahedra, edges with sixteen NiV4Ni8 cuboctahedra, faces with four equivalent VNi12 cuboctahedra, and faces with fourteen NiV4Ni8 cuboctahedra. There are four shorter (2.49 Å) and four longer (2.52 Å) Ni–Ni bond lengths. In the second Ni site, Ni is bonded to four equivalent V and eight equivalent Ni atoms to form NiV4Ni8 cuboctahedra that share corners with four equivalent NiV4Ni8 cuboctahedra, corners with eight equivalent VNi12 cuboctahedra, edges with twenty-four NiV4Ni8 cuboctahedra, faces with six equivalent VNi12 cuboctahedra, and faces with twelve NiV4Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V3Ni by Materials Project

NiV3 crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. V is bonded in a 6-coordinate geometry to two equivalent V and four equivalent Ni atoms. Both V–V bond lengths are 2.33 Å. All V–Ni bond lengths are 2.61 Å. Ni is bonded to twelve equivalent V atoms to form a mixture of edge and face-sharing NiV12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VNi3 by Materials Project

Ni3V is beta Cu3Ti-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. V is bonded to four equivalent V and eight equivalent Ni atoms to form VV4Ni8 cuboctahedra that share corners with four equivalent VV4Ni8 cuboctahedra, corners with eight equivalent NiNi12 cuboctahedra, edges with twenty-four NiV4Ni8 cuboctahedra, faces with eight equivalent VV4Ni8 cuboctahedra, and faces with ten NiV4Ni8 cuboctahedra. All V–V bond lengths are 2.52 Å. All V–Ni bond lengths are 2.53 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded to four equivalent V and eight Ni atoms to form NiV4Ni8 cuboctahedra that share corners with twelve equivalent NiV4Ni8 cuboctahedra, edges with eight equivalent VV4Ni8 cuboctahedra, edges with sixteen NiV4Ni8 cuboctahedra, faces with four equivalent VV4Ni8 cuboctahedra, and faces with fourteen NiV4Ni8 cuboctahedra. There are four shorter (2.50 Å) and four longer (2.52 Å) Ni–Ni bond lengths. In the second Ni site, Ni is bonded to twelve Ni atoms to form NiNi12 cuboctahedra that share corners with four equivalent NiNi12 cuboctahedra, corners with eight equivalent VV4Ni8 cuboctahedra, edges with eight equivalent VV4Ni8 cuboctahedra, edges with sixteen equivalent NiV4Ni8 cuboctahedra, faces with two equivalent VV4Ni8 cuboctahedra, and faces with sixteen NiV4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.52 Å.

36 MATERIALS SCIENCE↗