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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Cavity-assisted magnetization switching in a quantum spin-phonon chain

Néel order switching in antiferromagnets has typically required intense optical driving, leading to substantial heating and limited efficiency. By placing antiferromagnets inside a terahertz-driven optical cavity, we propose a multi-particle mechanism for Néel order switching that benefits from reduced heating. Our analysis reveals that phonons are indispensable to this mechanism. A driven cavity mode couples to a spin-phonon chain, with all excitations dissipating energy through external baths. Mean-field analysis shows that cavity photons induce sublattice spin-density imbalance—an intrinsic symmetry-breaking effect absent without the cavity. Contrary to known (1–10 V/nm) laser fields required to switch the Néel order, our mechanism enables switching at remarkably low laser fields (1–5 V/μm), selectively targeting low-energy and perpendicular magnon modes. By virtue of the suppressed heating, the switching remains highly tunable through laser fluence, damping, and photon loss, establishing a low-dissipation route toward cavity-assisted opto-spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Observation of Room-Temperature Range Magnetocaloric Effect in PrSr{sub 1−x}Pb{sub x}Mn{sub 2}O{sub 6} (0.4 ≤ x ≤ 0.6) Double-Perovskite Manganite System

The Pr(Sr{sub 1−x}Pb{sub x})Mn{sub 2}O{sub 6} (0.4 ≤ x ≤ 0.6) double-perovskite manganite samples have been produced by using a sol-gel method. The Rietveld refinement method has been used to analyse the structural properties, and the results show that all samples are crystallized in monoclinic structure with P21/n space group without any impurity phase. The temperature dependence of magnetization measurement shows that samples exhibit paramagnetic to ferromagnetic phase transition by decreasing temperature. The values of the T{sub C} are determined as 286, 280 and 278 K for x= 0.4, 0.5 and 0.6 in Pr(Sr{sub 1−x}Pb{sub x})Mn{sub 2}O{sub 6} samples, respectively. Isothermal applied magnetic field-dependent magnetization curves are used to determine both order of magnetic phase transition and magnetic entropy change (ΔS{sub M}) value. −ΔS{sub M} values are found as 3.68, 3.15 and 2.85 J kg{sup − 1} K{sup − 1} for PSPM-4, PSPM-5 and PSPM-6 samples, respectively. Additionally, magnetic phase transition of the samples is identified as second-order magnetic phase transition that indicates accompanying small thermal and magnetic hysteresis to the samples during the phase transition. Relative cooling power (RCP) values are determined as 282, 233 and 268 J kg{sup − 1} for PSPM-4, PSPM-5 and PSPM-6 samples, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A study of the physical properties of single crystalline Fe 5 B 2 P

Single crystals of Fe 5 B 2 PP were grown by self-flux growth technique. Structural and magnetic properties are studied. The Curie temperature of Fe 5 B 2 P is determined to be 655 ± 2 K. The saturation magnetization is determined to be 1.72 μ B /Fe at 2 K. The temperature variation of the anisotropy constant K 1 is determined for the first time, reaching 0:50 MJ/m 3 at 2 K, and it is comparable to that of hard ferrites. The saturation magnetization is found to be larger than the hard ferrites. The first principle calculations of saturation magnetization and anisotropy constant are found to be consistent with the experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural and magnetic properties of the CeCo 5 –CeZn 5 solid solution and potential improvements upon iron substitution

In an effort to create high-performance permanent magnets with reduced critical rare earth content, we explored the CeCo 5-x T x (T = transition metal or metalloid) family of compounds to investigate the effect of substitution on the material’s magnetic properties. In our exploration of the CeCo 5-x Zn x system, we discovered a continuous solid solution at 900 °C between the CeCo 5 and CeZn 5 binary phases with ferromagnetism existing from the CeCo 5 compound to the intermediate CeCo 2.75 Zn 2.25 compound. Single crystal studies were also conducted revealing a relatively large anisotropy field of 11.5 T at 300 K for Ce 0.96 Ta 0.04 Co 4.35 Zn 0.65 . Here, the addition of iron Ce 0.79 Ta 0.07 Co 3.77 Fe 0.89 Zn 0.47 yielded further increases in Curie temperature and saturation magnetization to 800 K and 85.5 emu/g, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Development of a He{sup 3}−He{sup 4} sub Kelvin active magnetic regenerative refrigerator (AMRR) with no moving parts

Current state of the art particle and photon detectors such as Transition Edge Sensors (TES) and Microwave Kinetic Inductance Detectors (MKID) use large arrays of sensors or detectors for space science missions. As the size of these space science detectors increases, future astrophysics missions will require sub-Kelvin cooling over larger areas. This leads to not only increased cooling power requirements, but also a requirement for distributed sub-Kelvin cooling. We propose an active Magnetic Regenerative Refrigerator (AMRR) that uses a Superfluid Magnetic Pump (SMP) to circulate liquid He{sup 3}−He{sup 4} through a magnetic regenerator to provide the necessary cooling at sub-Kelvin temperatures. Such system will be capable of distributing the cooling load to a relatively large array of objects. One advantage of using a fluid for heat transfer in such systems is to isolate components such as the superconducting magnets from detectors that are sensitive to magnetic fields. Another advantage of the proposed tandem AMRR is that it does not need Gas Gap Heat Switches (GGHS) to transfer heat during various stages of the magnetic cooling. Our proposed system consists of four superconducting magnets, one superleak, and three heat exchangers. It will operate continuously with no moving parts and it will be capable of providing the necessary cooling at sub-Kelvin temperatures for future space science applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Spin reorientation transition and near room-temperature multiferroic properties in a W-type hexaferrite SrZn{sub 1.15}Co{sub 0.85}Fe{sub 16}O{sub 27}

In this Letter, we investigate the magnetic and multiferroic properties of a W-type hexaferrite SrZn{sub 1.15}Co{sub 0.85}Fe{sub 16}O{sub 27}. Due to the strong planar contribution to the anisotropy provided by Co{sup 2+} ions, this hexaferrite shows a spin reorientation transition from easy-axis to easy-cone at 302 K, which is different from the onset temperature of ferroelectric polarization, 275 K. By applying magnetic field, a remarkable drop of polarization is observed, suggesting a large magnetoelectric effect in this multiferroics. The difference between spin reorientation and ferroelectric phase transition temperature as well as the origin of magnetoelectric effect are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Near fifty percent sodium substituted lanthanum manganites—A potential magnetic refrigerant for room temperature applications

Nearly half of lanthanum sites in lanthanum manganites were substituted with monovalent ion-sodium and the compound possessed distorted orthorhombic structure. Ferromagnetic ordering at 300 K and the magnetic isotherms at different temperature ranges were analyzed for estimating magnetic entropy variation. Magnetic entropy change of 1.5 J·kg{sup −1}·K{sup −1} was observed near 300 K. An appreciable magnetocaloric effect was also observed for a wide range of temperatures near 300 K for small magnetic field variation. Heat capacity was measured for temperatures lower than 300 K and the adiabatic temperature change increases with increase in temperature with a maximum of 0.62 K at 280 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The magnetic phase transition in Mn{sub 1.1}Fe{sub 0.9}P{sub 1−x}Ge{sub x} magnetocaloric alloys

Mn-Fe-P-Ge alloys are promising, low cost, high performance candidates for magnetic cooling applications based on the magnetocaloric effect. These alloys undergo a magnetic phase transition which induces a large entropy change (ΔS). Experimental and modeling studies were conducted to study this transition for varying Ge content. Landau theory and the Bean-Rodbell model were applied to Mn{sub 1.1}Fe{sub 0.9}P{sub 1−x}Ge{sub x} (x = 0.26, 0.3, and 0.32) melt spun ribbons to model the phase transition and the associated entropy change. The critical behavior of these alloys was studied. The critical composition range at which the cross over from first order to second order magnetic transition occurs was determined. The calculated thermodynamic values and critical temperatures were in good agreement with our experimental results. A high maximum entropy change (ΔS) of ∼44.9 J kg{sup −1} K{sup −1} was observed in Mn{sub 1.1}Fe{sub 0.9}P{sub 0.74}Ge{sub 0.26} in a 5 T applied magnetic field. The results suggest that Mn-Fe-P-Ge alloys are very attractive materials for near room temperature magnetic cooling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Large entropy change accompanying two successive magnetic phase transitions in TbMn{sub 2}Si{sub 2} for magnetic refrigeration

Structural and magnetic properties in TbMn{sub 2}Si{sub 2} are studied by variable temperature X-ray diffraction, magnetization, electrical resistivity, and heat capacity measurements. TbMn{sub 2}Si{sub 2} undergoes two successive magnetic transitions at around T{sub c1} = 50 K and T{sub c2} = 64 K. T{sub c1} remains almost constant with increasing magnetic field, but T{sub c2} shifts significantly to higher temperature. Thus, there are two partially overlapping peaks in the temperature dependence of magnetic entropy change, i.e., −ΔS{sub M} (T). The different responses of T{sub c1} and T{sub c2} to external magnetic field, and the overlapping of −ΔS{sub M} (T) around T{sub c1} and T{sub c2} induce a large refrigerant capacity (RC) within a large temperature range. The large reversible magnetocaloric effect (−ΔS{sub M}{sup peak} ∼ 16 J/kg K for a field change of 0–5 T) and RC (=396 J/kg) indicate that TbMn{sub 2}Si{sub 2} could be a promising candidate for low temperature magnetic refrigeration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Magnonic beam splitter: The building block of parallel magnonic circuitry

We demonstrate a magnonic beam splitter that works by inter-converting magnetostatic surface and backward-volume spin waves propagating in orthogonal sections of a T-shaped yttrium iron garnet structure. The inter-conversion is enabled by the overlap of the surface and volume spin wave bands. This overlap results from the demagnetising field induced along the transversely magnetised section(-s) of the structure and the quantization of the transverse wave number of the propagating spin waves (which are therefore better described as waveguide modes). In agreement with numerical micromagnetic simulations, our Brillouin light scattering imaging experiments reveal that, depending on the frequency, the incident fundamental waveguide magnonic modes may also be converted into higher order waveguide modes. The magnonic beam splitter demonstrated here is an important step towards the development of parallel logic circuitry of magnonics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

ALICE—An advanced reflectometer for static and dynamic experiments in magnetism at synchrotron radiation facilities

We report on significant developments of a high vacuum reflectometer (diffractometer) and spectrometer for soft x-ray synchrotron experiments which allows conducting a wide range of static and dynamic experiments. Although the chamber named ALICE was designed for the analysis of magnetic hetero- and nanostructures via resonant magnetic x-ray scattering, the instrument is not limited to this technique. The versatility of the instrument was testified by a series of pilot experiments. Static measurements involve the possibility to use scattering and spectroscopy synchrotron based techniques (photon-in photon-out, photon-in electron-out, and coherent scattering). Dynamic experiments require either laser or magnetic field pulses to excite the spin system followed by x-ray probe in the time domain from nano- to femtosecond delay times. In this temporal range, the demagnetization/remagnetization dynamics and magnetization precession in a number of magnetic materials (metals, alloys, and magnetic multilayers) can be probed in an element specific manner. We demonstrate here the capabilities of the system to host a variety of experiments, featuring ALICE as one of the most versatile and demanded instruments at the Helmholtz Center in Berlin-BESSY II synchrotron center in Berlin, Germany.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Magnetocaloric cycle with six stages: Possible application of graphene at low temperature

The present work proposes a thermodynamic hexacycle based on the magnetocaloric oscillations of graphene, which has either a positive or negative adiabatic temperature change depending on the final value of the magnetic field change. For instance, for graphenes at 25 K, an applied field of 2.06 T/1.87 T promotes a temperature change of ca. −25 K/+3 K. The hexacycle is based on the Brayton cycle and instead of the usual four steps, it has six stages, taking advantage of the extra cooling provided by the inverse adiabatic temperature change. This proposal opens doors for magnetic cooling applications at low temperatures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Spin-glass transition in Ni carbide single crystal nanoparticles with Ni{sub 3}C − type structure

Hexagonal shaped nanoparticles about 60 nm in size were successfully synthesized in tetraethylene glycol solution containing polyvinylpyrrolidone. By the analysis of the electron diffraction pattern, these were identified as a single crystal of Ni carbide with Ni{sub 3}C − type structure. Their magnetization curve at 5 K was not completely saturated under a magnetic field of 5 T. The thermomagnetization curves after zero-field cooling and after field cooling exhibited the magnetic cooling effect at low temperatures. Furthermore, the 2nd order nonlinear term of AC magnetic susceptibility exhibited a negative divergence at about 17 K. It is concluded that Ni carbide single crystal nanoparticles with the Ni{sub 3}C − type structure exhibit spin-glass transition at low temperatures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Magnetocaloric properties of Eu{sub 1−x}La{sub x}TiO{sub 3} (0.01 ≤ x ≤ 0.2) for cryogenic magnetic cooling

We report magnetic and magnetocaloric (MCE) properties of polycrystalline Eu{sub 1−x}La{sub x}TiO{sub 3} samples over a wide composition range (0.01 ≤ x ≤ 0.20). It is found that the ground state changes from antiferromagnetic for x = 0.01 (T{sub N} = 5.2 K) to ferromagnetic for x ≥ 0.03 and the ferromagnetic Curie temperature increases from T{sub C} = 5.7 K for x = 0.03 to T{sub C} = 7.9 K for x = 0.20. The x = 0.01 sample shows a large reversible isothermal magnetic entropy change of −ΔS{sub m} = 23 (41.5) J/kg K and adiabatic temperature change of ΔT{sub ad} = 9 (17.2) K around 6.7 K for a field change of μ{sub 0}ΔH = 2 (5) Tesla. Although the peak value of −ΔS{sub m} decreases as La content increases, it is impressive in x = 0.2(−ΔS{sub m} = 31.41 J/kg K at T = 7.5 K for μ{sub 0}ΔH = 5 T). The large value of MCE arises from suppression of the spin entropy associated with the localized moment (J = 7/2) of Eu{sup 2+}:4f{sup 7} ions. This large MCE over a wide compositional range suggests that the Eu{sub 1−x}La{sub x}TiO{sub 3} series could be useful for magnetic cooling below 40 K.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Conventional superconductivity in single-crystalline BiPt

Binary Bi-Pd/Pt systems have attracted a lot of interest because of their topologically nontrivial nature along with superconductivity. We report the structural and superconducting properties of high-quality single-crystalline BiPt using a comprehensive range of experimental techniques, including X-ray diffraction, electron microscopy, muon spin rotation/relaxation (𝜇⁢SR), magnetization, resistivity, and heat capacity. Our findings establish that BiPt is a weak type-II superconductor with a transition temperature (𝑇 𝑐 ) of 1.2 K which exhibits pronounced anisotropic superconducting characteristics attributed to its hexagonal crystal structure. Magnetization and electronic transport studies reveal that BiPt lies within the dirty limit, while 𝜇⁢SR and heat capacity data indicate conventional 𝑠-wave superconductivity that maintains time-reversal symmetry. Here, this work provides valuable insights into the pairing symmetry and superconducting mechanism of topologically trivial BiPt, a sound comparison system for other Bi-based topologically nontrivial superconductors.

Demagnetization↗
DOE OSTI2021

Meissner-London Susceptibility of Superconducting Right Circular Cylinders in an Axial Magnetic Field

Analysis of magnetic susceptibility of nonellipsoidal samples is a long-standing problem in experimental studies of magnetism and superconductivity. Here the quantitative description of the Meissner-London response (no Abrikosov vortices) of right circular cylinders in an axial magnetic field is given. Three-dimensional adaptive finite-element modeling is used to calculate the total magnetic moment ( m ) in a wide range of London penetration depth ( λ ) to sample size ( a ) ratios, λ /a. Furthermore, by fitting numerical solutions, the closed-form empirical magnetic susceptibility is obtained involving only sample dimensions and λ, thus providing a recipe for determining the London penetration depth from the precision measurements of the magnetic susceptibility. Detailed protocols of the experimental data analysis using the developed approach are given. The results can be readily extended to the most frequently used cuboid-shaped samples.

3-dimensional systems↗