S. Foner's research while affiliated with Massachusetts Institute of Technology and other places
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Publications (342)
Pulsed-field magnetization measurements up to 40 T by Faraday rotation were made for random alloy Cd1−xMnx Te with 0.1 < x < 0.5. At liquid helium temperature the magnetization can be separated into the sum of two components: a paramagnetic Brillouin-like part that saturates by B=15 T, and a part linear in B. For large x, the linear part dominates...
Dilute magnetic semiconductors (DMS), such as Cd1−xMnxTe, are excellent hosts for the study of disordered magnetic systems. In these diluted random alloys, neighboring magnetic ions form clusters through short range spin exchange interactions. A number of experiments [1-8] have been devoted to the investigation of the nearest-neighbor (NN) coupled...
The angular dependence of the upper critical fields, Hc(θ) for a set of NbTi-Ge superlattices were studied at various temperatures. The behavior of Hc(θ) at lower temperatures deviates from the Tinkham expression which is expected to be valid only in the Ginzberg-Landau regime close to Tc. We examine a model for calculating Hc(θ) involving the lowe...
Low-temperature magneto-luminescence studies are used to examine the in-plane valence-band dispersion in GaAs/GaPAs strained-layer-superlattice structures. The results provide a direct observation of valence-band mixing effects in strained-layer systems.
Theoretical and experimental studies of the effect of valence-band mixing upon the magneto-tran...
Contains reports on six research projects.
Magnetization steps from Mn2+ pairs in several single crystals of Zn1−xMnxO (0.0056<~x<~0.030), and in one powder (x=0.029), were observed. They were used to determine the four largest exchange constants (largest J’s), and the single-ion axial anisotropy parameter D. The largest two exchange constants, J1/kB=−18.2±0.5K and J1′/kB=−24.3±0.5K, were o...
A theory for the equilibrium low-temperature magnetization M of a diluted Heisenberg antiferromagnetic chain is presented. Only the nearest-neighbor (NN) exchange interaction is included, and the distribution of the magnetic ions is assumed to be random. Values of the magnetic fields Bi at the magnetization steps (MST's) from finite chains with two...
All materials possess a magnetic moment; techniques for measuring that bulk macroscopic property are defined here as magnetometry. This article reviews the most common techniques for measuring the total magnetic moments of small samples (volume ≤1 cm³ and/or mass ≤1 g). Several factors contribute to the bulk magnetic moment of a sample. Essentially...
The Fe3+ dimer in μ-oxalatotetrakis(acetylacetonato)Fe2(III) is ideally suited for a magnetization-step study. Using pulsed magnetic fields up to 500 kOe (50 T), all five predicted magnetization steps (MST’s) from this dimer were observed. The MST’s appeared as peaks in the differential susceptibility dM/dH. Using the convention in which the exchan...
Nanoparticles of ferrimagnetic NiFe2O4 and antiferromagnetic NiO exhibit a variety of anomalous magnetic properties. The lower coordination of surface spins is responsible in both cases for the observed behavior. This conclusion is supported by calculations of field-dependent spin distributions in these nanoparticles.
The differential susceptibility dM/dH of [Fe(salen)Cl]2 where salen is N,N′ethylenebis(salicylideneiminato), was measured in pulsed magnetic fields up to 550 kOe. The samples were in a capsule that was immersed in a liquid-helium bath maintained at a temperature 1.5<~Tbath<~4.2K. Three magnetization steps (MST’s) arising from energy-level crossings...
Magnetization-steps spectroscopy is used to determine exchange constants in dilute magnetic semiconductors and in molecular magnetism. The differential susceptibility dM/dH of [Fe salen Cl]2 was measured in pulsed magnetic fields up to 55 T. The samples were immersed in a 1.5 K liquid-helium bath. Three magnetization steps (MST's) arising from the...
The superconducting properties and microscopic characterization are presented for Nb3Sn, (Nb,Ta)3Sn and (Nb,Ti)3Sn conductors made using several different fabrication routes. The element concentration profiles at the grain boundaries, determined using STEM, leads to a pinning model that includes the pinning by normal boundaries and by the grain bou...
Anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz et al.).5 These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mössbauer spectra indicated that all of the material was magnetically ord...
Several anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously (Berkowitz, et al., Phys. Rev. Lett. 34, 594, 1975). These properties included low magnetization with a large differential susceptibility at high fields and shifted hysteresis loops after field cooling, while Mössbauer spectra indicated that...
Nanoparticles of ferrimagnetic NiFe2O4 and antifeiromagnetic NiO exhibit a variety of anomalous magnetic properties. The NiFe2O4 particles’ behavior is inteipreted in terms of a canted or disordered spin-glass-like surface state which is coupled to a core with bulk properties. This model is supported by calculations of spin distributions in these n...
The principles of several of the most popular macroscopic magnetic measurement techniques are discussed for the vibrating sample magnetometer, SQUID magnetometer, ac susceptometer, ac force magnetometer, and torque magnetometers. These types of instruments are available commercially as stand-alone computer-controlled systems, Selected examples of r...
The reaction of ferric chloride and β-diketones (HL) in alkaline methanol solution represents a good synthetic route to hexairon(III) clusters [MFe6-(OCH3)12(L)6]+ (M = Na, Li), which exhibit an unusual sixfold molecular symmetry. Single-crystal X-ray diffraction showed that the six octahedrally coordinated iron(III) ions define a ring and are link...
Nickel ferrite nanoparticles exhibit anomalous magnetic properties at low temperatures: low magnetization with a large differential susceptibility at high fields, hysteresis loops which are open up to 160 kOe, time-dependent magnetization in 70 kOe applied field, and shifted hysteresis loops after field cooling. We propose a model of the magnetizat...
On its 40th anniversary, I describe how the vibrating sample magnetometer (VSM) was developed and, later, how the very low frequency VSM, a flux‐integration device, was developed. The important features of the moving sample technique, detection coil symmetry, calibration, sensitivity, and image effects are discussed briefly. Some VSM adaptations di...
Several anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously by Berkowitz et al. These properties included low magnetization with a large differential susceptibility at high fields, shifted hysteresis loops after field cooling below 50 K, and Mössbauer spectra indicating a fraction of the material bein...
Critical current densities of multi-filamentary Nb3Al wire made with the Jelly-Roll process (JR) and mono-core powder metallurgy process (PM) wire were measured as a function of temperature and magnetic field. The temperature dependence of the resistive critical field Bc2 was measured in PM wires. There is a significant difference between these res...
The first of three expected magnetization steps (MSTs), due to the nearest-neighbor (NN) antiferromagnetic exchange J1 between Co2+ pairs in CdS(Co) and CdSe(Co), is observed by differential magnetization measurements in pulsed magnetic fields up to 60 T. In contrast with earlier results on CdS(Mn) which showed MSTs in pulsed fields much narrower b...
Faraday rotation experiments in pulsed magnetic fields to 60 T were used to determine the nearest-neighbor d-d exchange interaction constant ${\mathit{J}}_{1}$ for Co in ${\mathrm{Cd}}_{1\mathrm{$-${}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$S. A single broad step is observed in the magnetization at ${\mathit{B}}_{1}$=41 T. After correcting for sing...
The concentrations of elements at the grain boundaries and inside the grains of the A15 phase were measured in a variety of commercial and laboratory Nb<sub>3</sub>Sn, (Nb,Ta)<sub>3</sub>Sn and (Nb,Ti)<sub>3</sub>Sn multifilamentary wires. Scanning Transmission Electron Microscopy (STEM) was used to determine the concentrations with high spatial re...
This paper gives a brief historical review of the development of high magnetic fields and high field superconductors including brief summaries of the early developments of high magnetic fields and the Francis Bitter National Magnet Laboratory (FBNML). The start of the first revolution (when large critical currents in Nb<sub>3</sub>Sn were observed...
Cu artificial pinning centers (APCs) measuring 20 or 5 nm across were introduced to Nb<sub>3</sub>Sn and Nb<sub>3</sub>Sn(Ta) wire by means of powder metallurgy. The APCs increased the filament hardness by less than 10%. Stress anneals could be applied without affecting the Cu APC content or morphology. The Cu APCs led to a fine grained Nb<sub>3</s...
Cu(Sn) artificial pinning centers (APCs) were introduced into multifilamentary Nb 3 Sn wire using powder metallurgy Nb+Cu rods. In the composite Nb+Cu filaments the Cu ribbons had a thickness of either 20 or 5 nm before reaction. During the 600 °C anneal the APCs enhanced the reaction rate and reduced the Nb 3 Sn grain size to ≪20 nm. The Cu concen...
Pulsed field differential magnetization, dM/dB, and Faraday rotation measurements are reviewed in selected dilute magnetic semiconductors which required fields above 30 T for determining the antiferromagnetic exchange interactions between isolated pairs of magnetic ions or larger clusters. In some cases, nonequilibrium effects result in a narrowing...
We present an extensive study of the magnetization properties of high quality YBa2Cu3O7 and conventional low-temperature superconducting single crystals using a vibrating sample magnetometer. The experimental conditions cover a wide range of temperatures, applied fields (up to 30 T), and sweep rates. The experimentally measured linear relationship...
The synthesis of [Fe(OMe)2(O2CCH2Cl)]10, a molecular ferric wheel, from basic iron chloroacetate and ferric nitrate in methanol is described. Spectroscopic analysis of methanol solutions used to prepare the compound revealed a (μ-oxo)(μ-carboxylato)diiron(III) intermediate having terminal oxygen donor ligands. The structure of the crystalline ferri...
In superconductors the critical current densities are limited by the ability of the pinning centers in the material to pin flux lines. In A15-type superconductor wires, such as Nb3Sn, the pinning centers are the boundaries of A15 grains formed during the reaction heat treatment between the Nb and Sn at 650-750°C. The pinning behavior in these wires...
In conventional composite structures a property F can often be related to the properties of the individual components through the rule of mixtures (ROM). Metal-matrix structures in which the second metal B is finely dispersed can have properties that deviate strongly from the ROM. Several binary systems have been extensively investigated, notably C...
Superconducting Nb<sub>3</sub>Sn wire was produced by means of the
powder metallurgy process using Nb-2.9 at.% Ti and Sn-6.2 at.% Ga
powders to which small quantities of Cu, Ag or Cu+Ag powders were added.
Using heat treatments at 950°C and 750°C, these additions
increased the overall critical current density to 10<sup>8</sup> A/cm
<sup>2</sup> at...
The onset of the upper critical field Bc2(T) measured up to 60 T in powdered single-phase K3C60 and Rb3C60 yields Tc=19.5 and 28.4 K, Bc2(4.2 K)=30 and 55 T, (dBc2/dT)T=Tc=-2.80 and -3.85 T/K, and Ginzburg-Landau coherence lengths at 0 K of 31 and 24 Å, respectively. Bc2(T) appears to be that of a ‘‘conventional’’ superconductor showing paramagneti...
Analysis of fired rails from electromagnetic railgun indicates gross surface melting near the breach end of the rails. This effect is most likely caused by joule heating and arc erosion. To improve the mechanical behavior of the rail material, alloys of copper, such as Cu-0.6 Nb, has been used in the past with moderate success. More recently anothe...
Several scaling relations are inferred from magnetization data taken in fields up to 20 T on single crystal YBa2Cu3-xNixO7 where 0 less-than-or-equal-to x less-than-or-equal-to 0.03. A Bean-like critical state exists in the samples at high fields (less-than-or-similar-to 20 T) and low temperatures (4.2 K) regardless of x. Strong systematics are als...
Phase formation kinetics in Nb/Al multilayered thin films having overall compositions of 25, 33, 50, and 75 at. % Al have been investigated using scanning calorimetry, x‐ray diffraction, and cross‐sectional transmission electron microscopy. The first phase to form upon annealing the Nb/Al layered structure of all samples is the NbAl 3 intermetallic...
Powder metallurgy (PM) was used to fabricate Cu-Nb microcomposites both at the laboratory and intermediate industrial scales.
Ultimate tensile strengths (UTSs) of 1.6 and 1.035 GPa were obtained for the laboratory-and intermediate-scale composites,
respectively. Filament morphology and the microstructure of various microcomposites were examined wit...
The temperature dependence of the magnetic susceptibility for 1.5≪T≪300 K, the field dependence of the magnetization M(H), for 0≪H≪23 T and 1.5≪T≪15 K, and the temperature dependence of the heat capacity C(T), for 5≪T≪95 K are reported for the insulating distorted‐perovskite systems PrBaO 3 , TbBaO 3 , TbSrO 3 , and CeBaO 3 , and the pseudoternary...
Transport and magnetization measurements are presented for
YBa<sub>2</sub>Cu<sub>3-x</sub>Ni<sub>x</sub>O<sub>7</sub> single
crystals, where x ranges from 0.0 to 0.03. The presence of
nickel systematically sharpens the resistive transition of the material
in a high magnetic field, but it does not correlate with the critical
current as determined fr...
Superconducting Nb<sub>3</sub>Sn wire was produced by a powder
metallurgy method using Nb or Nb-2.9 at.% Ti powder in combination with
Sn- x at.% Ga powders ( x =3, 4.2, 6.2, and 9.0). Ga
additions to the Sn caused considerable solid solution hardening, which
improved its workability. It made the Nb-Sn(Ga) powder combination
convenient for swaging...
The values of critical temperatures for alloys of Pb- and SnMoâSâ were shown to be lower than those of the respective pure Chevrel phases. Chemical compositional analysis of the compounds revealed that the decreased {Tc} in the alloys are due to the off-stoichiometric compositions in the alloys. Although alloying slightly increased the values of th...
The values of critical temperatures for alloys of Pb- and SnMo{sub 6}S{sub 8} were shown to be lower than those of the respective pure Chevrel phases. Chemical compositional analysis of the compounds revealed that the decreased {Tc} in the alloys are due to the off-stoichiometric compositions in the alloys. Although alloying slightly increased the...
Phase Formation kinetics in the reaction of Nb/Al multilaycred thin films were investigated using scanning calorimetry, x-ray diffraction, and transmission electron microscopy. The first phase to form upon annealing the Nb/Al layered structure is the NbAl 3 intermetallic. Its formation is clearly identified by the calorimetry to be a two stage proc...
We investigated the phase formation sequence in the reaction of multilayer thin films of Nb/Al with overall compositions of 25 and 33 at.% AI. We report novel phenomena which distinguish thin-film reactions unequivocally from those in bulk systems. For sufficiently thin layers composition and stability of product phases are found to deviate signifi...
A powder metallurgy process using elemental powders was employed to fabricate Cu-Nb microcomposite wires. An ultimate tensile strength (UTS) of 1400 MPa and resistivity of 2.3μΩ cm were measured at 300 K for a Cu-15 vol % Nb composite. Details of the process and of the effect of deformation and heat treatment on the strength, filament morphology an...
We have developed a technique for preparation of cross-sectional transmission electron microscopy samples of reacted and unreacted Nb/Al multilayer thin films on sapphire substrates. The choice of substrate was found to be extremely important. Sapphire sputters more slowly than Nb and Nb-compounds and therefore makes it possible to obtain the elect...
We have investigated the phase formation sequence for the reaction of Nb and Al in multilayer films using cross‐sectional transmission electron microscopy and x‐ray diffraction. NbAl 3 is the first intermetallic phase to form. Contrary to previous reports, we find evidence from cross‐sectional transmission electron microscopy that the sigma phase,...
Magnetization steps (MSTs) were observed in Zn1-xCoxSe and Zn1-xCoxS using temperatures T < 1 K, steady magnetic fields up to 200 kOe, and pulsed fields up to ∼400 kOe. Unlike the MSTs observed earlier in other materials, these MSTs are due to pairs of distant-neighbor spins rather than to pairs of nearest-neighbor spins. For Zn1-xCoxSe the results...
Recently the NSF Division of Materials Research Panel on Large Magnetic Fields concluded that the opportunities for research and technology in high magnetic fields are compelling for support of a new national magnet laboratory with the following components as goals: (i) dc hybrid magnet facilities (water‐cooled magnets surrounded by superconducting...
The effect of an aluminum oxide layer at the interface of Al/Nb on phase formation in thin‐film binary diffusion couples was studied. Al/Nb bilayers with or without aluminum oxide at the interface were prepared by electron‐beam evaporation. The samples were annealed at a constant heating rate of 50 °C/min to temperatures in the range 800–950 °C, an...
The compound PrFe4P12, which has the cubic LaFe4P12 modified CoAs3 ‐type structure, orders antiferromagnetically, with TN=6.2 K and with several field‐induced magnetic transitions for T<TN, up to 5 T for T≪TN. Heat capacity measurements show the transition is a bulk effect, with magnetic entropy consistent with a magnetic doublet or triplet crystal...
A series of measurements of the structural, electrical, magnetic, and thermal properties are presented for the (Y1-xPrx)Ba2Cu3O7-y system. Orthorhombic samples for 0≤x≤1.0 were prepared for all the experiments performed. Unlike nearly all other systems where rare earth (R) are substituted for the Y cation in superconducting YBa2Cu3O7-y the substitu...
Internal quantum structures of Mn2+ spin clusters in Cd1-xMnxTe are studied by Faraday-rotation measurements up to 60 T at T~4 K. For x=0.1 we observe the contribution of Mn2+ triplet clusters, as well as the saturation of Mn2+ pairs. Overall good agreement between the experiments and a nearest-neighbor cluster model is obtained. By quantitative an...
The compound PrFeâPââ, which has the cubic LaFeâPââ modified CoAsâ-type structure, orders antiferromagnetically, with {ital T}{sub {ital N}}=6.2 K and with several field-induced magnetic transitions for {ital T}>{ital T}{sub {ital N}}, up to 5 T for {ital T}{much lt}{ital T}{sub {ital N}}. Heat capacity measurements show the transition is a bulk...
Resistive transitions of single crystal
Ba2YCu3-χNiχO7 were
studied in magnetic field up to 20 tesla. For dop concentrations of
χ = 0.01 and χ 0.03, the transition temperature in zero field
decreased from the undoped value of 88K to 82K and 76K respectively,
while the transition width †T (10%-90%) is still less than 1K.
Moreover, Ni-doping has a dr...
Magnetization steps due to nearest-neighbor Mn2+ pairs in Cd0.977Mn0.023S and Zn0.97Mn0.03S are much narrower in pulsed fields than expected from thermal broadening, and show a fine structure. These narrow steps imply a pair spin-lattice relaxation time much longer than 0.5 ms. An interpretation of the narrow steps, based on the Dzyaloshinski-Moriy...
Pulsed-field magnetization measurements in dilute magnetic semiconductors were made up to 55 T at 1.4 K in order to determine the nearest-neighbor antiferromagnetic exchange JNN for Mn2+ pairs. For Cd1-xMnxTe (x=0.047), JNN/kB=-6.2±0.2 K. This ‖JNN‖ was sufficiently small so that all five predicted ‘‘magnetization pair steps’’ due to pairs were obs...
The sequence of phases formed in the low-temperature reaction of
niobium and aluminium to form the A15 superconductor, Nb<sub>3</sub>Al,
was studied in high areal reduction powder metallurgy processed wire
samples. The reaction path observed was the same as that reported
previously for multilayer Nb/Al thin films. The reaction proceeds
without the...
Powder-metallurgy-processed Nb-25-at.% Al wires were annealed at
temperatures just below the melting temperature. Depending on anneal
conditions, the entire Nb-Al part of the wire could be rapidly quenched
as a metastable Al Nb(Al) solid solution with an Al concentration
exceeding 23 at.%. This A2 phase is sufficiently ductile to be bent
without in...
Powder metallurgy processing of Nb<sub>3</sub>Sn(Ti) wire was
scaled up to 75-mm-diameter billets, each containing 4 kg of pressed
powder composite. Prealloyed Nb-1.5-wt.% Ti powder was used for optimum
high-field properties. An initial hot extrusion step provided complete
consolidation and excellent integrity of the powder composite. Using the
ext...
Alternative approaches for producing stationary (nondestructive) pulsed fields above available dc fields are considered. Multilayer, high strength, wire-wound, steel reinforced, Cu/Nb metal-matrix microcomposite pulsed magnets achieving up to 68.4 T for a 5.6 ms half-period were developed. Such magnets are the preferred technology for further devel...
Previously reported temperature increases above 4.2 K in an immersion geometry in liquid <sup>4</sup>He at fields ≫19 T have been verified and examined. Magnetic forces (B dB/dx) above a threshold level of ∼21 T<sup>2</sup>/cm were found to trap <sup>4</sup>He bubbles near the center of the field. Significant heat input to the region (from conducti...
A description is given of a high-strength metal-matrix microcomposite Cu/Nb conductor used in a multilayer wire-wound pulsed field magnet. The 0.5-in inner diameter magnet was precompressed in a hardened-steel structure and cooled to 77 K. A maximum field of 68.4 T was generated for a 5.6-ms half-period at the maximum energy available with the avai...
Measurements are presented of the critical current density, J c , and parallel upper critical field, H c2‖ , for the refractory superconductor/insulator multilayer system NbN/AlN. A dramatic increase in J c , together with an increase of H c2‖ , is observed with decreasing NbN layer thickness. The J c enhancement arises from flux pinning in the AlN...
The structural, magnetic, and superconducting properties of the mixed compounds La/sub 1.85/Sr/sub 0.15/Cu/sub 1-//sub x/M/sub x/O/sub 4/ (0<x<0.3) (M = Ni or Zn) and YBa/sub 2/Cu/sub 3//sub -//sub x/Ni/sub x/O/sub 7//sub -//sub y/ (x = 0.25 or 0.5) were studied. dc resistance, Meissner, and shielding measurements have shown that both magnetic Ni a...
We present measurements of the properties of epitaxial thin films of superconducting YBa2Cu3O7-δ, with Tc about 90 K, transition widths of ∼2.5 K, and critical currents in excess of 105A/cm2 at 77 K. The temperature dependence of the upper critical field exceeds 4 T/K for fields parallel to the film (i.e., H⊥ to the c axis) and the anisotropy of th...
Studies are reported of the upper critical fields of Nb0.53Ti0.47-Ge multilayers consisting of thick Ge layers and varying-thickness Nb0.53Ti0.47 layers. Both the angular dependence and the temperature dependence of the upper critical fields indicate a dimensional crossover at a Nb0.53Ti0.47 layer thickness near 200 Å. All the 2D samples display a...
The photoluminescence intensity of InGaAs/GaAs strained layer single quantum wells with p-type doping was measured as a function of magnetic field. Two different experimental techniques were used, and both show a reduction of intensity with complete suppression occurring at B=35T. Self-consistent potential and energy level calculations indicate com...
The upper critical fields Bc2(T) were measured up to 28 T for R1Ba2Cu3O7-y, where R=Nd, Eu, Gd, Dy, Ho, Er, and Tm, and for YBa2Cu3O7-y. The midpoints (dBc2/dT)T=Tc cluster about (2.8±0.2) T/K, the Tc's=(93±2) K show a slight systematic decrease from Nd to Tm, and the extrapolated values of Bc2(0) cluster about (160±20) T. The wide range of normal-...
We have measured the upper critical field Bc2(T) of Y2-xBaxCuO4-y with x=0.4 near Tc in dc fields up to 20 T and at 77 K with pulsed fields to 45 T. The data yield (dBc2/dT)T=Tc=1.3 T/K and Tc=89.5 K for the midpoint of the resistive transitions, and (dBc2/dT)T=Tc=5+/-1 T/K and Tc=95.1 K for the onset. The estimates for Bc2(0) range from 80 to 320...
The upper critical fields Bc2(T) of La2-xSrxCuO4(x=0.15 and x=0.20) were measured near Tc in dc fields to 23 T and at 4.2 K with pulsed fields to 45 T. Resistive midpoint transitions for the x=0.15 sample yield &=2.2 T/K, Tc=38.1 K, and Bc2(0)=58 T assuming a dirty type-II superconductor with no Pauli paramagnetic limiting. Data for the onset yield...
We have measured the upper critical field B/sub c//sub 2/(T) of Y/sub 2-//sub x/Ba/sub x/CuO/sub 4-//sub y/ with x = 0.4 near T/sub c/ in dc fields up to 20 T and at 77 K with pulsed fields to 45 T. The data yield (dB/sub c//sub 2//dT)/sub T //sub = //sub T>c/ = 1.3 T/K and T/sub c/ = 89.5 K for the midpoint of the resistive transitions, and (dB/su...
Powder metallurgy (P/M) processed Nb 3 Sn(Ti) wires were made with alloyed Nb(Nb-1.2wt%Ti) powders using a Cu-45wt% (Nb-1.2wt%Ti) composite. Nominal areal reductions of about 10<sup>4</sup>were used and Sn was introduced by means of a central Sn core. With a Sn-5wt%Cu core a critical current density J c = 10<sup>4</sup>A/cm<sup>2</sup>at 4.2K was m...
The magnetization of the diluted antiferromagnetic system ${\mathrm{Cd}}_{1\mathrm{$-${}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te with 0.1$\le${}x$\le${}0.5 is examined up to fields of 40 T at liquid-helium temperature. The measured magnetization can be separated into the sum of two components: a paramagnetic Brillouin-type part that saturates by...
A series of multifilamentary (Nb-4at%Ta) 3 Sn wires with varying Sn content was examined inorder to optimize the high field performance. Various Sn thicknesses were plated onto sections of 0.15 mm (.006") o.d. multifilamentary wire for external bronze processing. Long heat treatments achieved almost complete conversion of the filaments to A15. A sy...
The upper critical fields B/sub c/â(T) of Laââ/sub x/Sr/sub x/CuOâ(x = 0.15 and x = 0.20) were measured near T/sub c/ in dc fields to 23 T and at 4.2 K with pulsed fields to 45 T. Resistive midpoint transitions for the x = 0.15 sample yield (dB/sub c/â/dT)/sub T //sub = //sub =/ = 2.2 T/K, T/sub c/ = 38.1 K, and B/sub c/â(0) = 58 T assuming a dirty...
In order to demonstrate the potential of powder metallurgy (P/M) process for fabrication of high field superconductors, intermediate scale (5 cm o.d. 15 cm long) billets were fabricated and processed industrially by hot extrusion. Precompacted powder composites of Cu-45wt%Nb and Cu-45wt%(Nb-1.2wt%Ti), each weighing more than 2kg, were extruded as s...
Low field magnetization measurements, including time dependent thermoremanent magnetization, on UxY1-xB4, show spin-glass behavior for 0.1 < x < 0.55. The paramagnetic-spin glass phase boundary is reentrant, with the freezing temperature reaching about 14 K for x = 0.3. The temperature dependence of the magnetic viscosity scales for the x = 0.2 and...
Magnetic polarons are ferromagnetic spin clusters created by the exchange interaction of a carrier spin (electron or hole) with localized spins embedded in a semiconductor lattice. They were first studied in magnetic semiconductors [1]; more recently, there have been extensive investigations [2] of polaron behavior in diluted magnetic semiconductor...
A multilayer wire‐wound pulsed field magnet was fabricated using a new metal‐matrix microcomposite Cu/Nb conductor. The 0.5‐in.‐i.d. magnet used square cross‐section Cu/Nb wire, precompressed in a hardened steel container and cooled to 77 K, to generate 68.4±1 T for a 5.6‐ms half‐period. The maximum field was generated using a 100‐kJ, 4‐kV capacito...
A dc magnetic field of 33.6±0.3 T was produced in a hybrid magnet whose central field was enhanced by a 3.5 T contribution from holmium pole pieces. The working (sample) volume was a 2‐mm gap between the 19‐mm‐diam×32‐mm‐long pole pieces tapered to 12‐mm‐diam faces. The magnetic field was measured with high‐field/low‐temperature Hall‐effect sensors...
The temperature dependence of the magnetic susceptibility, the low-temperature specific heat, and the field dependence of the high-field magnetization were measured for the pseudobinary system U(Inââ/sub x-italic/Sn/sub x-italic/)â for 0< or =x-italic< or =1. The results show a clear evolution from long-range antiferromagnetism for x-italic0.8 (Sn...
Powder metallurgy processed Nb 3 Sn(Ti) superconducting wires were fabricated with Sn x wt. % Ti cores for 0≤x≤3, 16 or 22 vol % cores, and a Cu 45 wt. % Nb composite. The processing used swaging, cold hydrostatic extrusions, wire drawing and heat treatments of 750 °C for two to four days. Nominal areal reductions of 10<sup>4</sup> were used. Hydri...
The temperature dependence of the magnetic susceptibility, the low-temperature specific heat, and the field dependence of the high-field magnetization were measured for the pseudobinary system U(In1-xSnx)3 for 0x1. The results show a clear evolution from long-range antiferromagnetism for x<0.45 (In rich) to a heavy-fermion region for 0.45x0.80 and...
Several approaches to fabricating Nb//3Al superconducting wires have been published in the last decade. These processes include: the Swiss roll, rapid quenching, mechanical alloying and powder metallurgy processing. This paper will address powder metallurgy (P/M) processing of Nb//3Al and Nb//3Sn. The recent measurements of critical current densiti...
Magnetization data in fields up to 210 kOe were obtained on Zn1-xMnxTe samples with x=0.031 and 0.040. At Tapeq21.4 K, a magnetization step was observed near 150 kOe. This step is attributed to a level crossing for pairs of nearest-neighbor (NN) Mn spins. The magnetic field at the center of the step gives J/kB=-10.0±0.8 K for the NN exchange consta...
The UX3 systems with X = Ga, In, Tl, Si, Ge, Sn and Pb are a particularly interesting class of uranium compounds because both their magnetic and electronic properties are drastically influenced by f-spd hybridization. We report resistivity, low temperature specific heat, magnetic susceptibility and high field magnetization results for the U(In1−xSn...
Evidence for magnetic field induced superconductivity in the pressure induced superconductor Eu0.9Ho0.1Mo6S8 is reported. Resistive measurements of Hc2 vs. T were made at four hydrostatic pressures (6, 8, 10, and 12 kbar) in applied magnetic fields up to 19 T and temperatures down to 1.3 K. By using hydrostatic pressure to fine tune Tc, and the exc...
A linear variation of magnetic susceptibility versus temperature is observed for UAl/sub 2/ for 3 K< or =T< or =10 K and for applied fields of 0.1, 1, 2, and 5 T. Although a quadratic dependence is not observed within this temperature range, the results are consistent with specific-heat measurements.
The upper critical fields, H/sub c/2, of SnMoâS/sub 8-x/O/sub x/ and PbMoâS/sub 8-x/O/sub x/ Chevrel-phase materials with controlled oxygen content were measured with dc and pulsed magnetic fields. The present results and those of many earlier investigations are explained by the presence of oxygen. Observations of increases in T/sub c/ and the vari...
A variety of ambient and high‐pressure experimental results reveal the interplay between magnetism and superconductivity in Ho‐doped samples of the pressure‐induced superconductor, EuMo 6 S 8 . Ho concentrations up to 50 at. % of the rare‐earth ions were used. High‐resolution magnetic measurements are consistent with the crystalline electric field...
A variety of ambient and high-pressure experimental results reveal the interplay between magnetism and superconductivity in Ho-doped samples of the pressure-induced superconductor, EuMo/sub 6/S/sub 8/. Ho concentrations up to 50 at. % of the rare-earth ions were used. High-resolution magnetic measurements are consistent with the crystalline electri...
Powder metallurgy processed Nb-Al wire with overall critical current densities, J c , at 4.2K up to 10<sup>4</sup>A/cm<sup>2</sup>at 19T has been investigated in more detail, Kramer plots and directly measured H c2 values of samples with different heat treatments show an increase in H c2 at 4.2K up to 24.5T. Test coils, using long lengths of wire,...
Analytical electron microscopic observations of longitudinal cross-sections of Nb-8 wt.% Al powder metallurgy processed wire are presented. Grains were found of unreacted Nb, Nb-Al which was identified as Al5 Nb-Al by convergent beam electron diffraction (CBED), and Nb-Al grains identified as Nb 2 Al by CBED. No unreacted Al is found. High resoluti...
Citations
... This class of materials is commonly referred to as metastable intermolecular composites [3][4][5][6][7]. The architectures of the majority of nano-energetics consist of powdered systems [2,[8][9][10][11][12][13][14][15][16][17][18][19] or multi-layered laminate structures [1,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. ...
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... + 8.8794 where X is the mole fraction of C in Mg(B 1-X C X ) 2 . [12,16,17] a) b) Figure 9 -a) a-axis lattice parameter (in Å) calculated from XRD peak positions and b) lattice C-content X in Mg(B 1-X C X ) 2 calculated from the data in Table I. applicability of the flux line lattice shear model (FLL) [31,32,37] following the general form: ...
... This results in correlation of ferromagnetism with carrier concentration and provides conditions for using the material as an effective spin injector [36]. The Hamiltonian which describes the magnetic properties of transition metal ion doped DMS NPs is the s-d(f) Hamiltonian proposed for ferromagnetic semiconductors [37] H s−d = H sp + H el + H sp−el . ...
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