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A method may include annealing a material including iron and nitrogen in the presence of an applied magnetic field to form at least one Fe 16 N 2 phase domain. The applied magnetic field may have a strength of at least about 0.2 Tesla (T).
In this grant, we executed a multi-year plan to develop an advanced Faraday-effect polarimeter-interferometer system to address both fluctuation and equilibrium diagnostic needs by providing a measurement of the plasma internal magnetic field fluctuations (including non-axisymmetric 3-D perturbations) and plasma vertical position. This diagnostic included both fast time response and low phase noise so that both the temporal dynamics of equilibrium quantities as well as high-frequency electromagnetic fluctuations could be measured simultaneously, adding new and unique measurement capabilities for the core of high-temperature plasmas. The combined polarimeter-interferometer diagnostic development was applied primarily to the tokamak magnetic configuration, focusing on high-performance regimes including H-mode, reversed shear advanced tokamak scenarios, and non-inductive current drive.
The invention provides a method for measuring the magnetic field of an electromagnetic component having the steps of: instrumenting one or more portions of an electromagnetic component by placing an optical fiber in electromagnetic communication with the one or more portions of said electromagnetic component; energizing the electromagnetic component; interrogating the optical fiber using light and an optical detector; and determining changes in the magnetic field incident on the optical fiber based on the detected changes in the light received by the optical detector.
Mn{sup II}(TCNE)I(OH{sub 2}) was isolated from the reaction of tetracyanoethylene (TCNE) and MnI{sub 2}(THF){sub 3}, and has a 2-D structure possessing an unusual, asymmetric bonded {mu}{sub 4}-[TCNE]{sup {sm_bullet}-}. Direct antiferromagnetic coupling between the S = 5/2 Mn{sup II} and S = 1/2 [TCNE]{sup {sm_bullet}-} leads to magnetic ordering as a canted antiferromagnet at a T{sub c} of 171 K.
We report the controlled integration, via dip pen nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 μ{sub B}) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 10{sup 2}, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.
Spin electronic structure of the Graphene/Pt interface has been investigated. A large induced spin-orbit splitting (∼80 meV) of graphene π states with formation of non-degenerated Dirac-cone spin states at the K{sup ¯}-point of the Brillouin zone crossed with spin-polarized Pt 5d states at Fermi level was found. We show that this spin structure can be used as a spin current source in spintronic devices. By theoretical estimations and micromagnetic modeling based on the experimentally observed spin-orbit splitting, we demonstarte that the induced intrinsic magnetic field in such structure might be effectively used for induced remagnetization of the (Ni-Fe)-nanodots arranged atop the interface.
We present a micromagnetic study of a ferromagnetically exchange-coupled composite free layer design for perpendicular magnetic tunnel junctions. The thermal stability factor and critical switching current density depend on the exchange coupling strength and effective anisotropy ratio between the sublayers of the composite free layer. The energy barrier increases with an increase of the exchange coupling strength until it reaches a plateau in the strong-coupling limit. An optimal exchange coupling strength exists that leads to the minimal critical switching current and a significant improvement of the figure of merit defined as the ratio between the energy barrier and critical switching current. This behavior is obtained for smaller device sizes with uniform reversal and larger sizes with domain wall reversal.
We use neutron scattering to investigate spin excitations in Sr ( Co 1 - x Ni x ) 2 As 2 , which has a c -axis incommensurate helical structure of the two-dimensional (2D) in-plane ferromagnetic (FM) ordered layers for 0.013 ≤ x ≤ 0.25 . By comparing the wave vector and energy dependent spin excitations in helical ordered Sr ( Co 0.9 Ni 0.1 ) 2 As 2 and paramagnetic SrCo 2 As 2 , we find that Ni doping, while increasing lattice disorder in Sr ( Co 1 - x Ni x ) 2 As 2 , enhances quasi-2D FM spin fluctuations. However, our band structure calculations within the combined density functional theory and dynamic mean field theory ( DFT + DMFT ) failed to generate a correct incommensurate wave vector for the observed helical order from nested Fermi surfaces. Furthermore, since transport measurements reveal increased in-plane and c -axis electrical resistivity with increasing Ni doping and associated lattice disorder, we conclude that the helical magnetic order in Sr ( Co 1 - x Ni x ) 2 As 2 may arise from a quantum order-by-disorder mechanism through the itinerant electron mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions.
Presentation describes project to develop spectroscopic diagnostic and modeling capability to measure temperatures, electron densities, and magnetic fields.
High energy–density, low–cost batteries are critically important to a variety of applications ranging from portable electronics to electric vehicles (EVs) and grid–scale storage. While tremendous research effort has been focused on new materials or chemistries with high energy–density potential, design innovations such as low–tortuosity thick electrodes are another promising path toward higher energy density and lower cost. Growing demand for fast–charging batteries has also highlighted the need for negative electrodes that can accept high rate charging without metal deposition; low tortuosity can be a benefit in this regard. However, a general and scalable fabrication method for low–tortuosity electrodes is currently lacking. Here an emulsion–based, magnetic–alignment approach to producing thick electrodes (>400 µm thickness) with ultrahigh areal capacity (up to ≈14 mAh cm –2 vs 2–4 mAh cm –2 for conventional lithium ion) is reported. The process is demonstrated for LiCoO 2 and meso–carbon microbead graphite. The LiCoO 2 cathodes are confirmed to have low tortuosity via DC–depolarization experiments and deliver high areal capacity (>10 mAh cm –2 ) in galvanostatic discharge tests at practical C–rates and model EV drive–cycle tests. Lastly, this simple fabrication method can potentially be applied to many other active materials to enable thick, low–tortuosity electrodes.
Purpose: To determine whether a relationship exists between the tumor volume (TV) or relative choline content determined using magnetic resonance spectroscopy imaging (MRSI) at 3T and the clinical prognostic parameters for patients with localized prostate cancer (PCa). Methods and Materials: A total of 72 men (mean age, 67.8 {+-} 6.2 years) were stratified as having low-risk (n = 26), intermediate-risk (n = 24), or high-risk (n = 22) PCa. MRSI was performed at 3T using a phased-array coil. Spectra are expressed as the total choline/citrate, total choline plus creatine/citrate, and total choline plus polyamines plus creatine/citrate ratios. The mean ratio of the most pathologic voxels and the MRSI-based TV were also determined. Results: The mean values of the total choline/citrate, total choline plus creatine/citrate, and total choline plus polyamine plus creatine/citrate ratios were greater for Stage T2b or greater tumors vs. Stage T2a or less tumors: 7.53 {+-} 13.60 vs. 2.31 {+-} 5.65 (p = .018), 8.98 {+-} 14.58 vs. 2.56 {+-} 5.70 (p = .016), and 10.32 {+-} 15.47 vs. 3.55 {+-} 6.16 (p = .014), respectively. The mean MRSI-based TV for Stage T2b or greater and Stage T2a or less tumors was significantly different (2.23 {+-} 2.62 cm{sup 3} vs. 1.26 {+-} 2.06 cm{sup 3}, respectively; p = .030). This TV correlated with increased prostate-specific antigen levels (odds ratio, 1.293; p = .012). Patients with high-risk PCa had a larger TV than did the patients with intermediate-risk PCa. A similar result was found for the intermediate-risk group compared with the low-risk group (odds ratio, 1.225; p = .041). Conclusion: Biomarkers expressing the relative choline content and TV were significant parameters for the localization of PCa and could be helpful for determining the prognosis more accurately.
In the last few years, the superconducting transition temperature, T c , of hydrogen-rich compounds has increased dramatically, and is now approaching room temperature. However, the pressures at which these materials are stable exceed one million atmospheres and limit the number of available experimental studies. Superconductivity in hydrides has been primarily explored by electrical transport measurements, whereas magnetic properties, one of the most important characteristic of a superconductor, have not been satisfactory defined. Here, we develop SQUID magnetometry under extreme high-pressure conditions and report characteristic superconducting parameters for Im-3m-H 3 S and Fm-3m-LaH 10 —the representative members of two families of high-temperature superconducting hydrides. We determine a lower critical field H c1 of ~0.82 T and ~0.55 T, and a London penetration depth λ L of ~20 nm and ~30 nm in H 3 S and LaH 10 , respectively. The small values of λ L indicate a high superfluid density in both hydrides. These compounds have the values of the Ginzburg-Landau parameter κ ~12–20 and belong to the group of “moderate” type II superconductors, rather than being hard superconductors as would be intuitively expected from their high T c s.
A sample holder design for high temperature measurements in a commercial MPMS SQUID magnetometer from Quantum Design is presented. It fulfills the requirements for the simultaneous use of the oven and reciprocating sample option (RSO) options, thus allowing sensitive magnetic measurements up to 800 K. Alternating current susceptibility can also be measured, since the holder does not induce any phase shift relative to the ac driven field. It is easily fabricated by twisting Constantan Copyright-Sign wires into a braid nesting the sample inside. This design ensures that the sample be placed tightly into a tough holder with its orientation fixed, and prevents any sample displacement during the fast movements of the RSO transport, up to high temperatures.
A compact coil setup, in conjunction with a high power current pulser, is presented; developed especially for time- and spin-resolved photoemission spectroscopy measuring the sample in magnetic remanence at room temperature. A novel approach is presented where the sample is switched in the stray field of a coil pair. This enables the electrical biasing of the sample without altering the electron trajectories due to field gradients introduced by the coils. The pulser driving the coils reaches a peak power of 1 MW at 1 kA with a switching frequency up to 10 kHz suitable for experiments, for example, with state of the art repetition rates of femtosecond laser systems.
We report on domain nucleation in nanowires consisting of Co/Pt multilayers with perpendicular magnetic anisotropy that are patterned by electron-beam lithography, sputter deposition, and lift-off processing. It is found that the nucleation field can be tuned by changing the geometry of the wire ends. A reduction of the nucleation field by up to 60% is achieved when the wire ends are designed as tips. This contrasts with the behavior of wires with in-plane anisotropy where the nucleation field increases when triangular-pointed ends are used. In order to clarify the origin of the reduction of the nucleation field, micromagnetic simulations are employed. The effect cannot be explained by the lateral geometrical variation but is attributable to a local reduction of the perpendicular anisotropy caused by shadowing effects due to the resist mask during sputter deposition of the multilayer.
The temperature dependence of the magnetic hyperfine field (B{sub hf}) at Mn atom sites was measured in LaMn{sub 2}(Si{sub (1−x)}Ge{sub x}){sub 2}, with 0 ≤ x ≤ 1, compounds with perturbed γ−γ angular correlation spectroscopy using {sup 111}In({sup 111}Cd) as probe nuclei in the temperature range from 20 K to 480 K. The results show a transition from antiferromagnetic to ferromagnetic ordering for all studied compounds when Ge gradually replaces Si and allowed an accurate determination of the Néel temperature (T{sub N}) for each compound. It was observed that T{sub N} decreases when Ge concentration increases. Conversely, the Curie temperature increases with increase of Ge concentration. This remarkable change in the behavior of the transition temperatures is discussed in terms of the Mn-Mn distance and ascribed to a change in the exchange constant J{sub ex}.
Collimation of positrons produced by laser-solid interactions has been observed using an externally applied axial magnetic field. The collimation leads to a narrow divergence positron beam, with an equivalent full width at half maximum beam divergence angle of 4° vs the un-collimated divergence of about 20°. A fraction of the laser-produced relativistic electrons with energies close to those of the positrons is collimated, so the charge imbalance ratio (n{sub e−}/n{sub e+}) in the co-propagating collimated electron-positron jet is reduced from ∼100 (no collimation) to ∼2.5 (with collimation). The positron density in the collimated beam increased from 5 × 10{sup 7} cm{sup −3} to 1.9 × 10{sup 9} cm{sup −3}, measured at the 0.6 m from the source. This is a significant step towards the grand challenge of making a charge neutral electron-positron pair plasma jet in the laboratory.
Using first-principles calculations within density functional theory, we investigate the electronic and magnetic properties of different 3d transition metal-Si atomic lines on silicon Σ3 (112) grain boundary, which can be formed through grain boundary segregation. We find that (i) Fe atoms occupy the substitutional sites at the grain boundary and form an Fe-Si atomic line, but the interaction between the Fe atoms is antiferromagnetic. (ii) The ferromagnetic stability increases with the atomic number of the transition metals and Co-Si atomic line is more stable in the ferromagnetic phase and shows a semimetallic behavior. We suggest that this special TM-Si atomic line formed by thermodynamically favorable transition metal segregation on Si grain boundary could be used in design of spin-dependent quantum devices.