Design of soft magnetic materials
Abstract

We present a strategy for the design of ferromagnetic materials with exceptionally low magnetic hysteresis, quantified by coercivity. In this strategy, we use a micromagnetic algorithm that we have developed in previous research and which has been validated by its success in solving the “Permalloy Problem”—the well-known difficulty of predicting the composition 78.5% Ni of the lowest coercivity in the Fe–Ni system—and by the insight it provides into the “Coercivity Paradox” of W. F. Brown. Unexpectedly, the design strategy predicts that cubic materials with large saturation magnetizationmsand large magnetocrystalline anisotropy constantκ1will have low coercivity on the order of that of Permalloy, as long as the magnetostriction constantsλ100, λ111are tuned to special values. The explicit prediction for a cubic material with low coercivity is the dimensionless number$$({c}_{11}-{c}_{12}){\lambda }_{100}^{2}/(2{\kappa }_{1})=81$$$\left({c}_{11}-{c}_{12}\right){\lambda }_{100}^{2}/\left(2{\kappa }_{1}\right)=81$for 〈100〉 easy axes. The results would seem to have broad potential application, especially to magnetic materials of interest in energy research.

Authors:
;
Publication Date:
NSF-PAR ID:
10362711
Journal Name:
npj Computational Materials
Volume:
8
Issue:
1
ISSN:
2057-3960
Publisher:
Nature Publishing Group
National Science Foundation
##### More Like this
1. Abstract

We present a proof of concept for a spectrally selective thermal mid-IR source based on nanopatterned graphene (NPG) with a typical mobility of CVD-grown graphene (up to 3000$$\hbox {cm}^2\,\hbox {V}^{-1}\,\hbox {s}^{-1}$$${\text{cm}}^{2}\phantom{\rule{0ex}{0ex}}{\text{V}}^{-1}\phantom{\rule{0ex}{0ex}}{\text{s}}^{-1}$), ensuring scalability to large areas. For that, we solve the electrostatic problem of a conducting hyperboloid with an elliptical wormhole in the presence of anin-planeelectric field. The localized surface plasmons (LSPs) on the NPG sheet, partially hybridized with graphene phonons and surface phonons of the neighboring materials, allow for the control and tuning of the thermal emission spectrum in the wavelength regime from$$\lambda =3$$$\lambda =3$to 12$$\upmu$$$\mu$m by adjusting the size of and distance between the circular holes in a hexagonal or square lattice structure. Most importantly, the LSPs along with an optical cavity increase the emittance of graphene from about 2.3% for pristine graphene to 80% for NPG, thereby outperforming state-of-the-art pristine graphene light sources operating in the near-infrared by at least a factor of 100. According to our COMSOL calculations, a maximum emission power per area of$$11\times 10^3$$$11×{10}^{3}$W/$$\hbox {m}^2$$${\text{m}}^{2}$at$$T=2000$$$T=2000$K for a bias voltage of$$V=23$$$V=23$V is achieved by controlling the temperature of the hot electrons through the Joule heating. By generalizing Planck’s theory to any grey body and derivingmore »

2. Abstract

We present a multiwavelength analysis of the galaxy cluster SPT-CL J0607-4448 (SPT0607), which is one of the most distant clusters discovered by the South Pole Telescope atz= 1.4010 ± 0.0028. The high-redshift cluster shows clear signs of being relaxed with well-regulated feedback from the active galactic nucleus (AGN) in the brightest cluster galaxy (BCG). Using Chandra X-ray data, we construct thermodynamic profiles and determine the properties of the intracluster medium. The cool-core nature of the cluster is supported by a centrally peaked density profile and low central entropy ($K0=18−9+11$keV cm2), which we estimate assuming an isothermal temperature profile due to the limited spectral information given the distance to the cluster. Using the density profile and gas cooling time inferred from the X-ray data, we find a mass-cooling rate$Ṁcool=100−60+90M⊙$yr−1. From optical spectroscopy and photometry around the [Oii] emission line, we estimate that the BCG star formation rate is$SFR[OII]=1.7−0.6+1.0M⊙$yr−1, roughly two orders of magnitude lower than the predicted mass-cooling rate. In addition, using ATCA radio data at 2.1 GHz, we measure a radio jet power$Pcav=3.2−1.3+2.1×1044$erg s−1, which is consistent withmore »

3. Abstract

We present analysis of 17,043 proton kinetic-scale current sheets (CSs) collected over 124 days of Wind spacecraft measurements in the solar wind at 11 samples s−1magnetic field resolution. The CSs have thickness,λ,from a few tens to one thousand kilometers with typical values around 100 km, or within about 0.1–10λpin terms of local proton inertial length,λp. We found that the current density is larger for smaller-scale CSs,J0≈ 6 nAm−2· (λ/100 km)−0.56, but does not statistically exceed a critical value,JA,corresponding to the drift between ions and electrons of local Alvén speed. The observed trend holds in normalized units:$J0/JA≈0.17·(λ/λp)−0.51$. The CSs are statistically force-free with magnetic shear angle correlated with CS spatial scale:$Δθ≈19°·(λ/λp)0.5$. The observed correlations are consistent with local turbulence being the source of proton kinetic-scale CSs in the solar wind, while the mechanisms limiting the current density remain to be understood.

4. Abstract

A method for modelling the prompt production of molecular states using the hadronic rescattering framework of the general-purpose Pythia event generator is introduced. Production cross sections of possible exotic hadronic molecules via hadronic rescattering at the LHC are calculated for the$$\chi _{c1}(3872)$$${\chi }_{c1}\left(3872\right)$resonance, a possible tetraquark state, as well as three possible pentaquark states,$$P_c^+(4312)$$${P}_{c}^{+}\left(4312\right)$,$$P_c^+(4440)$$${P}_{c}^{+}\left(4440\right)$, and$$P_c^+(4457)$$${P}_{c}^{+}\left(4457\right)$. For the$$P_c^+$$${P}_{c}^{+}$states, the expected cross section from$$\Lambda _b$$${\Lambda }_{b}$decays is compared to the hadronic-rescattering production. The$$\chi _{c1}(3872)$$${\chi }_{c1}\left(3872\right)$cross section is compared to the fiducial$$\chi _{c1}(3872)$$${\chi }_{c1}\left(3872\right)$cross-section measurement by LHCb and found to contribute at a level of$${\mathcal {O}({1\%})}$$$O\left(1%\right)$. Finally, the expected yields of$$\mathrm {P_c^{+}}$$${P}_{c}^{+}$production from hadronic rescattering during Run 3 of LHCb are estimated. The prompt background is found to be significantly larger than the prompt$$\mathrm {P_c^{+}}$$${P}_{c}^{+}$signal from hadronic rescattering.

5. Abstract

We perform path-integral molecular dynamics (PIMD), ring-polymer MD (RPMD), and classical MD simulations of H$$_2$$${}_{2}$O and D$$_2$$${}_{2}$O using the q-TIP4P/F water model over a wide range of temperatures and pressures. The density$$\rho (T)$$$\rho \left(T\right)$, isothermal compressibility$$\kappa _T(T)$$${\kappa }_{T}\left(T\right)$, and self-diffusion coefficientsD(T) of H$$_2$$${}_{2}$O and D$$_2$$${}_{2}$O are in excellent agreement with available experimental data; the isobaric heat capacity$$C_P(T)$$${C}_{P}\left(T\right)$obtained from PIMD and MD simulations agree qualitatively well with the experiments. Some of these thermodynamic properties exhibit anomalous maxima upon isobaric cooling, consistent with recent experiments and with the possibility that H$$_2$$${}_{2}$O and D$$_2$$${}_{2}$O exhibit a liquid-liquid critical point (LLCP) at low temperatures and positive pressures. The data from PIMD/MD for H$$_2$$${}_{2}$O and D$$_2$$${}_{2}$O can be fitted remarkably well using the Two-State-Equation-of-State (TSEOS). Using the TSEOS, we estimate that the LLCP for q-TIP4P/F H$$_2$$${}_{2}$O, from PIMD simulations, is located at$$P_c = 167 \pm 9$$${P}_{c}=167±9$ MPa,$$T_c = 159 \pm 6$$${T}_{c}=159±6$ K, and$$\rho _c = 1.02 \pm 0.01$$${\rho }_{c}=1.02±0.01$ g/cm$$^3$$${}^{3}$. Isotope substitution effects are important; the LLCP location in q-TIP4P/F D$$_2$$${}_{2}$O is estimated to be$$P_c = 176 \pm 4$$${P}_{c}=176±4$ MPa,$$T_c = 177 \pm 2$$${T}_{c}=177±2$ K, and$$\rho _c = 1.13 \pm 0.01$$${\rho }_{c}=1.13±0.01$ g/cm$$^3$$${}^{3}$. Interestingly, for the water model studied, differences in the LLCP location from PIMD and MD simulations suggest that nuclear quantum effectsmore »