Paramagnetic Alloys Research Articles

Achieving strength–ductility synergy in novel paramagnetic Fe-based medium-entropy alloys through deep cryogenic deformation

Achieving strength–ductility synergy in novel paramagnetic Fe-based medium-entropy alloys through deep cryogenic deformation

Influence of magnetic field on the mechanical behavior of friction stir processed paramagnetic alloy

The study investigated the influence of an externally applied static magnetic field (MF) on the mechanical behavior of a friction stir processed paramagnetic 1100 aluminum (Al 1100) alloy. The aim was to take advantage of the solid-state friction stir processing (FSP) technique to modify the microstructure and further improve the properties by testing in the presence of MF. Al 1100 was tested in tension under different static MFs (B = 0, 150, 1000, 1400, 1800, and 2200 Gauss) perpendicular to the stress axis. The strong effect of a comparatively weak static MF was observed on the elongation of both base and processed Al 1100 alloy, in both rolling and transverse directions, attributed to the magneto-plasticity effect (MPE) where the motion of dislocations in crystals is influenced in the presence of magnetic fields. Amongst the different mechanisms associated with MPE, the major effect in the current study was observed from the magnetization force, spin transition, and increase in strain energy of dislocations. This knowledge will open new lanes to improve the properties of a processed sample by exposing it to an MF which is a non-contact, pollution-free route; saving time and cost by avoiding in-between thermo-mechanical steps to break the cast microstructure.

Influence of platinum content (X) in the LaNi5PtX catalyst and reaction conditions on the properties of ferromagnetic Ni-filled CNTs

This research highlights the synthesis of carbon nanostructures using the catalytic chemical vapor deposition (CCVD) method, a hybrid process combining chemical vapor deposition (CVD) and Gas-Solid Heterogeneous Catalysis (GSHC). Intermetallic catalysts, LaNi5Ptx (x = 0, 0.05, 0.5, 1.0), were fabricated through an arc melting procedure to serve as templates for the catalytic conversion of carbon precursors into solid materials. These catalysts, featuring the ferromagnetic transition metal Ni, tend to aggregate into larger particles, reducing the rate of hydrocarbon cracking at the catalyst surface. Rare earth metals like Lanthanum were introduced to form an alloy with a higher melting point to prevent thermal aggregation. Additionally, Pt was incorporated to modify the catalytic properties of the alloy. The study primarily explores the impact of catalyst composition on carbon nanotube (CNT) production. The introduction of platinum content to the catalyst influences the rate at which Ni is filled. The research aimed to alter the catalyst's composition by varying platinum doping in the Pauli paramagnetic lanthanum nickel alloy (LaNi5) to understand the growth mechanism and morphological variations of Ni-filled CNTs. Platinum and lanthanum oxides significantly influence nickel filling in CNTs, resulting in an increased filling rate as the catalyst's Pt content varies from 0 to 1.0. However, higher Pt doping content disrupts the CNT structure with spontaneous nickel encapsulation.

Electromagnetic Property Modulation of Flaky Ferromagnetic 304 Stainless-Steel Powders for Microwave Absorption at Elevated Temperatures

Soft magnetic metallic absorbents suffer from severe oxidation, reduction in permeability and deterioration in microwave absorption when exposed to high temperatures. In this study, we prepared flaky 304 stainless-steel powders as new microwave absorbents via deformation-induced ferromagnetism. The 304 stainless-steel powders showed significant increases in saturation magnetization (Ms) from 1.03 to 82.46 emu/g when their shape was changed from spheroids to flakes; the Ms further increased to 92.29 emu/g after heat treatment at 500 °C in air. The permeability of 304 alloy powders also showed an obvious increase after ball milling and remained roughly stable after heat treatment at 500 °C in air. Moreover, the permittivity exhibited a sharp decrease after heat treatment, enabling the improvement of impedance matching and microwave absorption. After heat treatment at 500 °C in air for 100 h, the simulated reflection loss of 304 stainless-steel powders with wax still showed attractive levels, giving a minimum value of −22 dB and remaining below −6 dB over 8.5–16.5 GHz at a thickness of 2 mm. Our work can help to include paramagnetic alloy systems as new microwave absorbents for working in harsh environments.

Development of Fast Decay-Energy Spectroscopy With Magnetic Microcalorimeters

Decay energy spectroscopy (DES) is an increasingly important radiometric technique arising from the unique thermal detection physics and the precision of low-temperature microcalorimetry. DES can enable high-precision analysis of very small amounts of radioactive material with simple and rapid sample preparation, making it a key new tool for nuclear safeguards, nuclear forensics, the improvement of nuclear data, measurements of absolute activity, and other applications. For problems in nuclear safeguards and nuclear forensics it is highly desirable to increase the count rates achievable in DES, while maintaining simple and rapid sample preparation. In this report we describe progress in a new project to achieve high count rates in DES by taking advantage of the physics of magnetic microcalorimetry. We describe the results of initial modeling and experiment to validate the idea, a sample fabrication technique suitable for nuclear materials laboratories, the preparation and initial tests of paramagnetic Au-Er alloy in thin foil form, and the development of a sensing coil geometry that will perform well with the increased-thickness sensor used in the new technique.

Effect of chromium variation on evolution of magnetic properties in laser direct energy additively processed CoCrxFeNi alloys

The soft magnetic behavior of laser directed energy deposited CoCrxFeNi (x = 0 - 24 at.% Cr) alloys has been investigated as a function of chromium content. The saturation magnetization of these CoCrxFeNi alloys monotonically decreased with increasing concentration of Cr, and exhibited paramagnetic behavior at room temperature for equiatomic CoCrFeNi alloy composition. Similarly, the Curie temperature (Tc) of the ferromagnetic CoFeNi alloy linearly decreased with Cr content, while the paramagnetic equiatomic alloy indicated a ferromagnetic transition temperature of 94 K. Interestingly, all the as-deposited alloys exhibited coercivity values less than 2 Oe irrespective of the Cr content. The results indicate that the magnetic behavior of the ferromagnetic CoFeNi alloy can be systematically tuned with addition of antiferromagnetic Cr, and the additive manufacturing route was successful in rapid processing alloys of any desired composition, in a high throughput manner, with negligible chemical variation. These findings are promising for the fabrication of components for applications demanding gradient magnetic coatings and alloys.

Investigation on Magnetization, Magnetocalory, Magnetoresistance, and Electric Properties of Ni-Mn Based Heusler Alloy

The magnetic and electrical characteristics of Ni-Mn quinary Heusler alloys are studied in the current work. The results concern the materials’ magnetic and electrical behavior. The physical property measurement system (PPMS) and superconducting quantum interference device (SQUID) were used at various magnetization levels to determine the results. The addition of Fe helps to form the alloy into a smart memory alloy with magnetocrystalline anisotropy, twin border mobility, and varied magnetic and martensite transition temperature characteristics. Character changes in the superparamagnetic (SPM) and paramagnetic (PM) alloys occur between 26 and 34 °C. The curves are supported by the alloy’s martensitic transition temperature change. A large refrigeration capacity is identified in the alloy. These properties are an indication of the alloys’ application prospects. Entropy change helps to detect the inverse magnetocaloric effect in the alloy, whereas adiabatic temperature change helps identify the origin and validity of reverse magnetic properties. The transition temperature changes occur when austenite’s sigma is larger than that of martensite, and as the magnetic field increases, the temperature declines. Isothermal magnetization curves, a large (MR)/B value at low and high magnetic fields, and temperatures near the transformation point suggest that small-crystal Heusler alloys have tremendous promise for low and high magnetic field magnetoresistance applications.

First-principles study on structural, mechanical, and electronic properties of REAuBi2 (RE = La–Pr, Sm) intermetallic compounds

Rare earth noble metals compounds have a variety of physical properties, such as heavy fermions, topological, superconductivity, and so on. In this paper, the cohesive energy, mechanical, electrical, and magnetic properties of REAuBi2 (RE=La-Pr, Sm) and the mechanical properties of REAu (RE=La-Pr, Sm) were studied by first-principles calculations. The calculated cohesive energies of REAuBi2 are negative, indicating the stable structures of REAuBi2. The comparison between the mechanical properties of REAuBi2 and REAu, including the bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio, under ideal conditions is carried out. Electronic density of states, band structure, and phonon spectrum of REAuBi2 are also studied and discussed. LaAuBi2 alloy is in the paramagnetic state, while PrAuBi2 and SmAuBi2 alloys are in antiferromagnetic order obtained by the results of Birch–Murnagha equation fitting of cell volume and energy.

Creating a Ferromagnetic Ground State with Tc Above Room Temperature in a Paramagnetic Alloy through Non-Equilibrium Nanostructuring.

Materials with strong magnetostructural coupling have complex energy landscapes featuring multiple local ground states, thus making it possible to switch among distinct magnetic-electronic properties. However, these energy minima are rarely accessible by a mere application of an external stimuli to the system in equilibrium state. A ferromagnetic ground state, with Tc above room temperature, can be created in an initially paramagnetic alloy by nonequilibrium nanostructuring. By a dealloying process, bulk chemically disordered FeRh alloys are transformed into a nanoporous structure with the topology of a few nanometer-sized ligaments and nodes. Magnetometry and Mössbauer spectroscopy reveal the coexistence of two magnetic ground states, a conventional low-temperature spin-glass and a hitherto-unknown robust ferromagnetic phase. The emergence of the ferromagnetic phase is validated by density functional theory calculations showing that local tetragonal distortion induced by surface stress favors ferromagnetic ordering. The study provides a means for reaching conventionally inaccessible magnetic states, resulting in a complete on/off ferromagnetic-paramagnetic switching over a broad temperature range.

Development of high-resolution capacitive Faraday magnetometers for sub-Kelvin region.

High-sensitivity capacitive Faraday magnetometers were developed for static DC magnetization measurements in a sub-Kelvin region that can be used with 3He-4He dilution refrigerators (∼50 mK) and 3He refrigerators (∼0.28K). For high-resolution magnetization measurements, the background magnetization of the force-sensing capacitor should be as small as possible, compared with the magnetization value of a measured specimen. In this study, we succeeded in reducing the background of the capacitor in both low- and high-field regions by compensating for the diamagnetic response of a thin quartz plate, making use of Pauli-paramagnetic alloys and Van Vleck paramagnets as a counter magnetization for a diamagnetic signal. Having established an ultra-high-sensitivity capacitor, we achieved a resolution of 10-5 (∼10-5-10-6) emu in the low- (high-) field region below (above) 1T. In particular, the newly developed capacitors with a Van Vleck paramagnet Pr0.1La0.9Be13 and paramagnetic MgAl alloys are demonstrated to be very useful for high-resolution magnetization measurements at milli-Kelvin temperatures in low and high magnetic fields, respectively.

Effect of Strain Rate and Measuring Temperature on Elastocaloric Effect and Multi-caloric Properties of Co37.5 Ni34.5 Al28 Paramagnetic Shape Memory Alloy

Effect of Strain Rate and Measuring Temperature on Elastocaloric Effect and Multi-caloric Properties of Co37.5 Ni34.5 Al28 Paramagnetic Shape Memory Alloy

A comparative study of solid-solution strengthening in Cr-Co-Ni complex concentrated alloys: The effect of magnetism

The effect of magnetism on the solid solution strengthening (SSS) of CrxCoyNi1–x–y alloys formulated by Varvenne’s and Toda-Caraballo’s (TC’s) models has been investigated comparatively by first-principles. It is found that for a reliable estimation of the model parameters for the paramagnetic (PM) and ferromagnetic (FM) alloys one should adopt the atomic radii and elastic moduli of the constituent metals corresponding to the same magnetic state. Furthermore, we show that Varvenne’s model underestimates the SSS when compared to the experimental data, while TC’s model correctly predicts the SSS of PM CrxCoyNi1–x–y alloys when adopting the PM parameters as inputs. Therefore, the magnetic states should be correctly accounted when estimating the atomic radii and elastic moduli of the constituent elements as input parameters for both models to capture the SSS in complex concentrated alloys properly.

Evolution of the Fe-on-Ti and Ti-on-Fe interfaces under thermal treatment

The different interface width and alloy composition of the Fe-on-Ti and Ti-on-Fe interfaces has been concluded recently from conversion-electron Mössbauer spectroscopy and x-ray reflectivity measurements of Ti/57Fe/Ti trilayers. Now it is shown by Mössbauer spectroscopy analysis that the asymmetric interfaces of the as-prepared samples result in different evolution of the phase compositions at the two interfaces under heat treatments below 300 °C. Room temperature conversion-electron Mössbauer spectroscopy measurements indicate that at the Ti-on-Fe interface the amount of both the paramagnetic and magnetic alloy components increase while at the Fe-on-Ti interface the amount of the paramagnetic alloy increases at the expense of the magnetic alloy component. The results are explained by the different thickness of the magnetic alloy at the two interfaces and the consequently different degree of layer formation.

Structural, thermo-elastic, electro-magnetic and thermoelectric attributes of quaternary CoNbMnX (X = Al, Si) Heusler alloys

This investigation consists of performing the structural, thermodynamic, electronic, magnetic and thermoelectric characteristics of the quaternary Heusler CoNbMnX (X = Al, Si) alloys using DFT within Wien2k code. Our calculations show that the atomic arrangement of the two alloys CoNbMnAl and CoNbMnSi is Type-I. From the elastic constant and the formation energy values, these compounds are predicted to be mechanically and thermodynamically stable, thus can be formed experimentally. The calculated values of their bulk modulus and cohesive energy values show that CoNbMnSi is more rigid than CoNbMnAl. From the analysis of the electronic properties, CoNbMnAl is identified to be paramagnetic and semiconductor alloy with 0.15 eV narrow indirect (Γ-X) band gap. Whereas, CoNbMnSi is characterized as a ferromagnetic alloy with half-metallicity character having a total magnetic moment of 1μB. The charge density contours and Fermi surface, predict a combined covalent and ionic bond between the atoms of CoNbMnX alloys. The calculated thermoelectric parameters assume that these alloys tend to behave as p-type with the same thermoelectric efficiency for either charge carriers; hole or electron. Depending on the high Seebeck coefficient value and ZT = 1 of the present alloys, potential applications are predicted, such as spin injection materials and spintronic applications.

Detecting and determining the nature of an anomalous x-ray optical effect in two-Layer substrate–coating systems

The authors have detected an anomalous X-ray optical effect in the Ni(1−x)Wx/TiN system, which consists of a rise in the intensity of certain diffraction lines of the substrate with increasing coating thickness. Based on the observed effect, this article has conceptualized the optimization of the architecture of two-layer systems with a substrate of TiN-coated NiW paramagnetic alloys, which provides an increase in the current-carrying capacity of second generation high temperature superconductors (2G HTS).

Theoretical modeling of interstitial carbon impurities in paramagnetic Fe-Mn alloys

We present a generalization of a model that takes into account the magnetic disorder of paramagnetic host with interstitial point defects towards the case of alloy hosts. In the framework of disordered local moment approach combined with magnetic sampling method, we calculate solution enthalpy of carbon impurity in the paramagnetic fcc Fe-Mn steels. First, we use the magnetic special quasirandom structure (M-SQS) method for simulation of the paramagnetic state in Fe-Mn alloys without impurity. Here, Fe and Mn atoms are randomly distributed at the sites of a supercell following the chemical SQS method. Next, to calculate the energies for various magnetic realizations around the interstitial carbon impurity, we vary the position of the impurity within the SQS. Our calculations show that in alloys containing $\ensuremath{\sim}20$ at. % Mn, the solution enthalpy of carbon reduces compared to the pure fcc-Fe. By analyzing the local and global effects of impurity on the properties of the matrix, we discuss various factors that could increase the carbon solubility in high-manganese austenitic steels.

Enhanced magnetostriction of Tb–Dy–Fe via simultaneous ⟨111⟩-crystallographic orientation and -morphological alignment induced by directional solidification in high magnetic fields

The giant magnetostriction exhibited by pseudobinary Tb–Dy–Fe compounds has attracted considerable attention for use in magneto-mechanical actuators and sensors. However, simultaneously producing a crystallographic orientation and a morphological alignment of the (Tb,Dy)Fe2 phase along the ⟨111⟩ direction has proven difficult and inhibits further increase in the desired property. This work demonstrates that, by coupling the directional solidification and a high magnetic field, a ⟨111⟩-orientation and -alignment were simultaneously created. In addition, the pores and the defects in the alloys were eliminated, leading to an enhancement of the magnetostrictive performance. Analyses indicate that the controlled growth of the (Tb,Dy)Fe2 crystal was owing to the collaboration of the multiple magnetic field effects on both the liquid and the solid phases during the directional solidification. Specifically, the magnetic torque induced a rotation of the crystals aligning their easy axis of magnetization (i.e., ⟨111⟩) along the magnetic field direction. Further, the Lorentz force stabilized the directional growth of the crystals by suppressing the convection, while the magnetic force exerted a compressive stress on the paramagnetic alloy melt to remove the gases in the melt. As a result, a highly ⟨111⟩-oriented and -aligned and defect-free Tb–Dy–Fe compound was produced. This strategy may also be expanded to other alloy systems whose phases exhibit a magnetic anisotropy and thereby fabricate anisotropic functional compounds.

Flattening of isothermal magnetic entropy change versus temperature curve in amorphous Fe–Mn–Mo–B ribbons

Microstructure, Curie temperature and isothermal magnetic entropy change of the amorphous Fe70Mn10Mo5B15 alloy in the as-quenched state and after annealing within the amorphous state at Ta1=723K and after the accumulative annealing at Ta1=723K and then at Ta2=753K for 0.5 h have been studied. The transmission Mössbauer spectra recorded at 300K are typical of a paramagnetic amorphous alloy and do not reveal distinct changes on annealing. The spectra in all cases are decomposed into a set of symmetric quadrupole doublets ascribed to the amorphous phase and a single line stemming from medium range ordered (MRO) regions which are paramagnetic at room temperature. The volume fraction of such MRO regions is small and increases only slightly on annealing. The Curie temperature of the amorphous phase decreases from 298 K in the as-quenched state to 268 K after the annealing at Ta1 and then increases to 282 K after the accumulative heat treatment at Ta1 and Ta2 due to invar effect. The isothermal magnetic entropy change of the alloy exhibits the “caret like” behavior with the peak values near the Curie points of the amorphous phase. The composites consisted of two adherent ribbons with different mass fraction (α) subjected to the annealing and made of two ribbons in the as-quenched state and after the heat treatment at Ta1 show the flat maxima of the magnetic entropy change in the temperature spans 14K and 34K for α=0.7 and α=0.5 in the former and latter composite, respectively. Parameter α denotes the mass fraction of the ribbon annealed at Ta1 in the composites. The flat maximum of the magnetic entropy change is obtained for the composite made of two ribbons with the same chemical composition but different thermal history. The refrigerant capacity (RC) of the amorphous Fe70Mn10Mo5B15 alloy is about 115 J/kg in the as-quenched state and decreases slightly on annealing. RC is enhanced for the composites in comparison with their components.

Influence of Mn content on the intrinsic energy barriers of paramagnetic FeMn alloys from longitudinal spin fluctuation theory

First-principles calculations were performed to investigate the influence of Mn content on the intrinsic energy barriers (IEBs) of paramagnetic FeMn alloys with face-centered cubic (fcc) structure. The IEBs were derived from the free energies accounting for longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the quantitative description of IEBs and their alloying dependencies at finite temperature. The unstable stacking and unstable twinning fault energies of the fcc phase slightly decrease with Mn content, whereas the intrinsic stacking fault energy (γisffcc) is predicted to monotonically increase. This latter finding contradicts the experimentally reported, local minimum of γisf in the fcc/hexagonal close-packed (hcp) coexistence region. The partitioning of Mn during the fcc/hcp phase transition is proposed to reconcile theory and experiment. Both temperature and impurities ([C] and Cr) hardly influence the monotonic concentration dependence of γisffcc but considerably alter the magnitude. The fcc/hcp interfacial energy is nearly independent of Mn concentration in contrast to the parabolic dependence predicted in thermodynamic modeling. In contrast to the fcc phase, the estimated intrinsic stacking fault energy of the ideal hcp structure monotonically decreases with Mn content and temperature. A high twinnability is predicted at 450 K within the stability field of the paramagnetic fcc FeMn alloys.

Elastic properties of paramagnetic austenitic steel at finite temperature: Longitudinal spin fluctuations in multicomponent alloys

We propose a first-principles framework for longitudinal spin fluctuations (LSFs) in disordered paramagnetic (PM) multicomponent alloy systems and apply it to investigate the influence of LSFs on t ...