Antiferromagnetic Alloys Research Articles

Enhancing the degradation rate and biomineralization nature of antiferromagnetic Fe-20Mn alloy by groove pressing.

The Fe-Mn alloys are potential candidates for biodegradable implant applications. However, the very low degradation rates of Fe-Mn alloys in the physiological environment are a major disadvantage. In this study, the degradation rate of a Fe-20Mn alloy was improved using the groove pressing (GP) technique. Hot rolled sheets of 2 mm thickness were subjected to GP operation at 1000°C. Uniform fine-grained (UFG) Fe-Mn alloys were obtained using the GP technique. The influence of GP on the microstructure, mechanical properties, degradation behavior in simulated body fluid (SBF), surface wettability, biomineralization, and cytocompatibility was investigated and compared to the annealed (A Fe-Mn) and rolled (R Fe-Mn) sample. The groove-pressed Fe-Mn (G Fe-Mn) alloy had a grain size of approximately 40 ± 16 μm whereas the A Fe-Mn and R Fe-Mn samples had grain sizes of 303 ± 81 and 117 ± 14.5 μm, respectively. Enhanced strength and elongation were also observed with the G Fe-Mn sample. The potentiodynamic polarization test showed the highest Icorr, lowest polarization resistance, and lowest Ecorr for the G Fe-Mn sample among all other samples indicating its higher degradation rate. The weight loss data from immersion tests also shows that the percentage of weight loss increases with time indicating the accelerated degradation behavior of the sample. The static immersion test showed an enhancement in weight loss of 0.46 ± 0.02% and 1.02 ± 0.05% for R Fe-Mn and G Fe-Mn samples, respectively, than A Fe-Mn sample (0.31 ± 0.03%) after 56 days in immersion in SBF. The greater biomineralization tendency in UFG materials is confirmed by the G Fe-Mn sample's stronger hydroxyapatite deposition. When compared to the A Fe-Mn and R Fe-Mn samples, the G Fe-Mn sample has a better wettability, which promotes higher cell adhesion and vitality, showing higher biocompatibility. This study demonstrates that Fe-20Mn processed by GP has potential applications for the manufacture of biodegradable metallic implants.

Antiferromagnetic Cr-Mn alloys: Crystal structure, magnetic anisotropy, and exchange bias in magnetron-sputtered polycrystalline thin films

In this paper we study the formation of the antiferromagnetic Cr-Mn alloys with body-centered cubic crystal structure, and their capability to act as a pinning layer for the exchange bias effect in magnetron-sputtered polycrystalline films. By means of X-ray diffractometry, executed in different geometries, we perform a thorough analysis of Ta/Cr-Mn/Ta films, which results in the construction of a room-temperature phase diagram of Cr-Mn. These results combined with magnetic measurements of films with adjacent antiferromagnetic Cr-Mn and ferromagnetic Fe20Ni80 layers allow us to establish the conditions for the observation of the exchange bias effect, the maximum blocking temperature Tb of which can be as high as 540 K. Employing a specialized measurement protocol, we estimate the effective anisotropy constant Keff, whose values help to explain thickness dependence of the exchange bias field in structures with a Cr-Mn pinning layer.

Magnetic properties, phase diagram and low-temperature specific heat of Ni50Mn50-xSbx alloys

This study examines the magnetic properties and temperature-composition phase diagram of the Ni50Mn50-xSbx alloys. The addition of Sb into the antiferromagnetic Ni50Mn50 alloy introduces ferromagnetic interaction, resulting in a sudden decrease in the Néel temperature. The characteristic regions of ferromagnetic (FM) and antiferromagnetic (AFM) interactions were determined on temperature-composition phase diagram, as well as compositional dependence of Néel temperature was computed. Increase of Sb content gives rise to an interplay between AFM and FM interactions, leading to the emergence of a spin glass-like state. We identified six distinct magnetic phases in the Ni50Mn50-xSbx system, encompassing AFM, paramagnetic, and FM martensite, as well as spin glass, and paramagnetic and FM austenite. Importantly, this behavior may extend to other Ni50Mn50-xZx (Z = In, Sn) alloys, where addition of Z elements leads to the introduction of FM interaction. Moreover, a significant impact of magnetic ordering on low-temperature specific heat is demonstrated. Neglecting the magnetic contribution in ferromagnetic phase leads to the overestimation of electronic specific heat coefficient by factor of 2.

Medical Imaging Compatibility of Magnesium- and Iron-Based Bioresorbable Flow Diverters.

Bioresorbable flow diverters are under development to mitigate complications associated with conventional flow-diverter technology. One proposed advantage is the ability to reduce metal-induced artifacts in follow-up medical imaging. In the current work, the medical imaging compatibility of magnesium- and iron-based bioresorbable flow diverters is assessed relative to an FDA-approved control in phantom models. Bioresorbable flow diverters, primarily composed of braided magnesium or antiferromagnetic iron alloy wires, were compared with an FDA-approved control flow diverter. The devices were assessed for MR imaging safety in terms of magnetically induced force and radiofrequency heating using 1.5T, 3T, and 7T field strength clinical scanners. The devices were deployed in phantom models, and metal-induced image artifacts were assessed in the 3 MR imaging scanners and a clinical CT scanner following clinical scan protocols; device visibility was assessed under fluoroscopy. The magnesium-based bioresorbable flow diverter, iron-based bioresorbable flow diverter, and the control device all demonstrated MR imaging safety in terms of magnetically induced force and radiofrequency heating at all 3 field strengths. The bioresorbable flow diverters did not elicit excessive MR imaging artifacts at any field strength relative to the control. Furthermore, the bioresorbable flow diverters appeared to reduce blooming artifacts in CT relative to the control. The iron-based bioresorbable flow diverter and control device were visible under standard fluoroscopy. We have demonstrated the baseline medical imaging compatibility of magnesium and antiferromagnetic iron alloy bioresorbable flow diverters. Future work will evaluate the medical imaging characteristics of the bioresorbable flow diverters in large-animal models.

Perpendicular magnetic anisotropy induced by antiferromagnetic Mn-Pd alloy films: Dual effects of exchange and spin-orbit coupling

Ferromagnetic (FM) films with perpendicular magnetic anisotropy (PMA) are crucial building blocks of state-of-the-art perpendicular magnetic devices. This study investigated the effects of triggering PMA in FM thin films by applying ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-based antiferromagnetic (AFM) thin films with strong AFM exchange coupling from Mn and high spin-orbit coupling from Pd atoms. Our results reveal that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films can trigger PMA in Co/Ni films with weak in-plane magnetic anisotropy at room temperature through either ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-facilitated interfacial perpendicular crystalline anisotropy (spin-orbit coupling, $x \ensuremath{\ge}10%$) or incorporation of them with antiferromagnet-induced exchange coupling ($x \ensuremath{\le}10%$). In Co/Fe films with strong in-plane magnetic anisotropy, Mn-rich ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films ($x \ensuremath{\le}10%$) can induce stable PMA at low temperatures through concurrently enhanced spin-orbit coupling and antiferromagnet-induced exchange coupling across the AFM--FM interface. Our research clarifies the dual effects of exchange and spin-orbit coupling in ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films, which trigger the PMA of adjacent FM films. This indicates that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films are promising candidates for achieving controllable PMA.

First-principles theoretical analysis of magnetically tunable topological semimetallic states in antiferromagnetic DyPdBi

A number of compounds in the family of rare-earth half-Heusler alloys have been predicted to be topologically nontrivial semimetals, classified as Weyl, triple-point, and Dirac semimetals based on the multiplicity of degeneracy of the nodal points or crossing of linearly dispersed electronic bands. Here, we present a first-principles theoretical characterization of the electronic topology of the antiferromagnetic half-Heusler alloy DyPdBi. In the antiferromagnetic state preserving ${C}_{3v}$ symmetry of the crystal, DyPdBi is a triple-point semimetal hosting four triply degenerate nodes along the threefold symmetry axis of the Brillouin zone. In contrast, the antiferromagnetic state of DyPdBi with local magnetic moments on Dy rotated to a direction perpendicular to the ${C}_{3}$ axis breaks the threefold rotational symmetry, and hosts four Weyl nodes in its Brillouin zone. Our calculations of the Berry curvature of their electronic states clearly show that the triple-point fermions of DyPdBi exhibit a signature peak in the anomalous Hall conductivity, while the Weyl fermions do not contribute to anomalous Hall conductivity. As these two topologically distinct magnetic states are separated by a small energy difference of $\ensuremath{\approx}$15 meV, we expect them to be switchable with a magnetic field or spin torque and distinguishable experimentally from anomalous Hall conductance.

An in-situ study of low thermal expansion and internal stress evolution in FeMn alloys

The mechanism of low thermal expansion phenomenon in antiferromagnetic FeMn alloys needs to be revealed. In this work, the evolution of lattice thermal expansion and internal stress in FeMn alloys was investigated by in-situ synchrotron X-ray diffraction during thermal cycling. Preceding the martensitic transformation, the coefficient of lattice thermal expansion (CLTE) decreased and the full width at half maximum (FWHM) of the diffraction peaks broadened abnormally. The evolution of the lattice thermal expansion and the FWHM were both reversible and isotropic. The additional reflection spots around the fundamental diffraction spots in the electron diffraction patterns of austenite and the dispersed nano-scale martensite embryos in austenite observed in the dark field TEM images proves the existence of premartensitic transformation. Similar phenomena were found in FeMn Invar alloy, which indicate that the Invar effect is closely related to the internal stress evolution caused by premartensitic transformation. • In this paper, many abnormal phenomena were observed in the Fe Mn alloys. The lattice thermal expansion behaviors and internal stress evolution in FeMn alloys was investigated by in situ synchrotron X-ray diffraction. The correlation between low thermal expansion property and premartensitic transformation were revealed by comparing the similar abnormal phenomena during Invar effect and the premartensitic transformation. The highlights are as follows: • During the Invar effect of Fe 27Mn alloy and preceding the martensitic transformation of Fe 24Mn alloy, the coefficient of thermal expansion decreased and the FWHM of diffraction peaks of austenite increased abnormally. The evolution of thermal lattice strain and FWHM was reversible and isotropic. • Transmission electron microscopy observations confirmed that there are massive martensite embryos embedded in austenite phase during Invar effect and premartensitic transformation. The existence of martensite embryos caused the abnormal increase of FWHM and may be related to the low thermal expansion behavior of FeMn alloy. • These similar phenomena imply a close relationship between the mechanism of Invar effect and the premartensitic transformation in FeMn alloy. • Our results may help to reveal the relationship between Invar effect and premartensitic transformation in antiferromagnetic Invar alloys, and lead to an in-depth understanding of the mechanism of low expansion property.

Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium

Spin torque is a promising tool for driving magnetization dynamics for computing technologies. These torques can be easily produced by spin-orbit effects, but for most conventional spin source materials, a high degree of crystal symmetry limits the geometry of the spin torques produced. Magnetic ordering is one way to reduce the symmetry of a material and allow exotic torques, and antiferromagnets are particularly promising because they are robust against external fields. We present spin torque ferromagnetic resonance (ST-FMR) measurements and second harmonic Hall measurements characterizing the spin torques in antiferromagnetic iron rhodium alloy. We report extremely large, strongly temperature-dependent exotic spin torques with a geometry apparently defined by the magnetic ordering direction. We find the spin torque efficiency of iron rhodium to be (207 \ifmmode\pm\else\textpm\fi{} 94)% at 170 K and (88 \ifmmode\pm\else\textpm\fi{} 32)% at room temperature. We support our conclusions with theoretical calculations showing how the antiferromagnetic ordering in iron rhodium gives rise to such exotic torques.

Flexible Spin Valves: Interlayer Interaction and Deformation Sensitivity

Exchange-coupled spin valves based on ferromagnetic alloys CoFeNi and antiferromagnetic alloy FeMn are obtained on flexible polyimide substrates by magnetron sputtering. The magnetoresistive properties of films and microstrips of spin valves are measured at various degrees of bending deformation of the sample. The behavior of the dependence of the deformation sensitivity of the spin valve on the interaction between the magnetic layers and on the arrangement of the anisotropy axes with respect to the deformation vector is characterized. It is found that the deformation sensitivity decreases with an increase in the interval between the fields of magnetization reversal of the free and fixed layers in the spin valve.

Consequences of Co-doping on the magnetic and magnetofunctional behavior of the antiferromagnetic Mn5Si3 alloy

The structural, magnetic, and electrical dc transport properties of Co-doped hexagonal Mn5Si3 alloys of nominal compositions Mn5−xCoxSi3 (x = 0.1, 0.3, 0.5) have been investigated. The doped alloys were found to crystallize in hexagonal D88 type structure. The shift in the collinear to non-collinear antiferromagnetic transition temperature towards the lower temperature is found to be slow with increasing Co-concentration compare to the Ni-doped alloys. However, both Ni and Co-doping provide positive chemical pressure in the system. Slower change in the valence electron concentration (e∕a ratio) with Co-doping plays the crucial role behind such observation. Incomplete field-induced non-collinear to collinear antiferromagnetic transition in the Co-doped alloys is another critical observation of the present work. A possible explanation for such behavior has been mooted in terms of local minimas’ disappearance between parent and product phases in the free energy landscape. Besides, various vital properties of Mn5Si3 alloy like, inverted hysteresis behavior, magnetocaloric effect, and magnetoresistance are found to be significantly affected by Co-doping.

Optical properties of the antiferromagnetic Heusler alloy Ru2CrGe

The results of optical measurements in the long wavelength infra-red (IR) range on the antiferromagnetic Heusler alloy Ru2CrGe with a Néel temperature of 13 K are reported. At 9 K there is absence of a Drude component in the absorption coefficient indicating the insulating nature of Ru2CrGe at this temperature. The absorption coefficient was observed to increase steeply around 50–70 cm−1 at all temperatures measured in this study.

Growth and Characterisation of Antiferromagnetic Ni2MnAl Heusler Alloy Films

Recent rapid advancement in antiferromagnetic spintronics paves a new path for efficient computing with THz operation. To date, major studies have been performed with conventional metallic, e.g., Ir-Mn and Pt-Mn, and semiconducting, e.g., CuMnAs, antiferromagnets, which may suffer from their elemental criticality and high resistivity. In order to resolve these obstacles, new antiferromagnetic films are under intense development for device operation above room temperature. Here, we report the structural and magnetic properties of an antiferromagnetic Ni2MnAl Heusler alloy with and without Fe and Co doping in thin film form, which has significant potential for device applications.

Understanding magnetic phase coexistence in Ru2Mn1−xFexSn Heusler alloys: A neutron scattering, thermodynamic, and phenomenological analysis

The random substitutional solid solution between the antiferromagnetic (AFM) full-Heusler alloy Ru$_2$MnSn and the ferromagnetic (FM) full-Heusler alloy Ru$_2$FeSn provides a rare opportunity to study FM-AFM phase competition in a near-lattice-matched, cubic system, with full solubility. At intermediate $x$ in Ru$_2$Mn$_{1-x}$Fe$_x$Sn this system displays suppressed magnetic ordering temperatures, spatially coexisting FM and AFM order, and strong coercivity enhancement, despite rigorous chemical homogeneity. Here, we construct the most detailed temperature- and $x$-dependent understanding of the magnetic phase competition and coexistence in this system to date, combining wide-temperature-range neutron diffraction and small-angle neutron scattering with magnetometry and specific heat measurements on thoroughly characterized polycrystals. A complete magnetic phase diagram is generated, showing FM-AFM coexistence between $x \approx 0.30$ and $x \approx 0.70$. Important new insight is gained from the extracted length scales for magnetic phase coexistence (25-100 nm), the relative magnetic volume fractions and ordering temperatures, in addition to remarkable $x$-dependent trends in magnetic and electronic contributions to specific heat. An unusual feature in the magnetic phase diagram (an intermediate FM phase) is also shown to arise from an extrinsic effect related to a minor Ru-rich secondary phase. The established magnetic phase diagram is then discussed with the aid of phenomenological modeling, clarifying the nature of the mesoscale phase coexistence with respect to the understanding of disordered Heisenberg models.

Nanocrystallization, magnetic properties and bending ductility of antiferromagnetic Mn-doped FeSiBCuPC alloys induced by micro-compressive stress annealing

Insufficient amorphous forming ability (AFA) and thermal instability have always been the bottleneck restricting the application of high Fe content iron-based nanocrystalline soft magnetic materials. In this work, the effects of micro-compressive stress annealing (MCSA) on microstructure, soft magnetic and mechanical properties of high Fe content FeSiBCuPCMn alloys were systematically investigated. We demonstrate that Mn doping effectively increases the AFA of the alloys and improves the thermal stability of the amorphous matrix. The change of coercivity (Hc) is closely related to the grain size, which depends on the Mn content and annealing process. It clearly shows that a small amount of Mn doping (≤3 at%) and MCSA can inhibit the excessive growth of α-Fe grains and reduce the grain size. Moreover, the low Mn-doped amorphous alloys exhibit good bending ductility even after annealing at appropriate conditions. After MCS-annealing at 420 °C for 10 min, the Mn-doped Fe85−xSi1.3B9P4Cu0.5C0.2Mnx (≤3 at%) nanocrystalline alloys exhibit comprehensive and excellent soft magnetic and mechanical properties, such as high Bs of 1.79–1.87 T, low Hc of 4.6–9.9 A/m and low Hv of 737–867.

Evolution of diverse Hall effects during the successive magnetic phase transitions in Mn2.5Fe0.6Sn0.9 Kagome-lattice alloy

Evolution of diverse Hall effects due to successive magnetic transitions has been observed in Mn2.5Fe0.6Sn0.9 by suitable chemical substitution of Fe in Mn3.1Sn0.9. This noncollinear antiferromagnetic alloy exhibits a Neel temperature of 325 K. Upon cooling from 325 K, a magnetic phase transition from noncollinear antiferromagnetism to ferromagnetism occurs at 168 K due to the tilting of magnetization towards c axis. Above this temperature, anomalous Hall resistivity ranged from 0.6 to 1.3 μΩ cm has been observed in noncollinear antiferromagnetic state. Below this temperature, a topological Hall effect (THE) starts to appear due to the non-vanishing scalar spin chirality arising from the noncoplanar spin structure. Further decreasing temperature to 132 K, another magnetic transition happens, resulting in the coexistence of ferromagnetism and antiferromagnetism, so that a Hall plateau with large hysteresis below 70 K is yielded. A hysteresis as high as ∼80 kOe is obtained in ρ xy -H at 15 K. However, the Hall plateau disappears and only anomalous Hall effect (AHE) persists when further decreasing the temperature to 5 K. The present study provides a picture of diverse magneto-transport properties correlated to the variable spin structures driven by magnetic phase transitions.

Mn-site doping and its effect on inverted hysteresis and thermomagnetic irreversibility behavior of antiferromagnetic Mn5Si3 alloy

The structural and magnetic behavior of Mn-site doped intermetallic manganese silicide alloys of nominal compositions Mn5−xAxSi3 (x = 0.05, 0.1, 0.2 and A = Ni, Cr) have been investigated with a focus to the inverted hysteresis behavior and thermomagnetic irreversibility. Room temperature x-ray powder diffraction data confirm that all the doped alloys crystallize in hexagonal D88 type structure with space group P63/mcm. The doped alloys are found to show paramagnetic–collinear antiferromagnetic (AFM2)–noncollinear antiferromagnetic (AFM1) transitions during cooling from room temperature. A significant decrease in the critical values of both AFM1–AFM2 transition temperatures and fields have been observed with the increasing Ni/Cr concentration. Inverted hysteresis loop, field-induced arrest, and thermomagnetic arrest, the key features of the undoped Mn5Si3 alloy, are found to be significantly affected by the Mn-site doping and eventually vanishes with 4% doping.

First-principles study of magnetism and phase stabilities of V2 based antiferromagnetic Heusler alloys

We investigate the phase stability and magnetism of V2 based antiferromagnetic semiconductors by first-principles calculations. We first analyze the phase stability of the designed alloys by calculating the convex hull and find that keeping Al atoms in the Z sites is crucial to guarantee the stability against the segregation. The V2YAl (Y=V, Nb, and Ta) systems have relatively small hull distances and Néel temperatures higher than 1000 K are evaluated. The strong antiferromagnetic coupling between V atoms is rapidly decreasing with increasing the number of electrons due to the appearance of ferromagnetic double-exchange interaction. By applying a uniaxial strain to induce tetragonal distortion, a relatively large magneto-crystalline anisotropy energy is obtained for V2TaAl. It is claimed that V2YAl are thought to be good candidates for antiferromagnetic spintronics including gate-tunable magnetic properties.

Effect of non-magnetic Ag-doping on magnetic and magnetofunctional properties of MnNiGe alloy

Systematic investigations on Ag-doped MnNiGe alloys of nominal compositions MnNi1−xAgxGe (x = 0.10, 0.15 and 0.20) have been performed through dc magnetic measurements in ambient as well as in high pressure conditions. All the Ag-doped alloys undergo martensitic type structural phase transition with a monotonic decrease in transition temperature with increasing Ag concentration. Room temperature x-ray powder diffraction data confirm the presence of both hexagonal and orthorhombic phase for 10% Ag-doped alloy whereas, 15% and 20% Ag-doped alloys are found to be purely hexagonal in nature. Gradual incorporation of ferromagnetic interaction with increasing Ag-concentration in otherwise antiferromagnetic alloy is clear from the magnetic investigations. Application of external hydrostatic pressure further favors ferromagnetism. In addition, these Ag-doped alloys also show a reasonably high magnetocaloric effect around the magnetic and structural transition temperatures which makes these alloys important for magnetic cooling applications. The robustness of the observed magnetocaloric properties have also been checked by high pressure measurements.

Transport properties of shell-ferromagnetic Heusler precipitates in decomposed Ni49.8Mn45.1Sn5.1 and decomposition limit for Ni50Mn50−xSnx alloys

Shell-ferromagnetism is observed in Mn-rich NiMn-based Heusler alloys as a result of phase-separation. Off-stoichiometric NiMn-based Heusler alloys decompose into a dual-phase composite when annealed under a magnetic field. As a result of this process, an initially anti-ferromagnetic Heusler alloy gains hard-ferromagnetic properties with a nearly 10 Tesla coercive field of a core/shell structured precipitate. In the present study, Ni50.1Mn42.1Sn7.8 and Ni50.4Mn36.6Sn13.0 alloys are investigated for magnetic and structural instabilities and shell-ferromagnetic decomposition to obtain information on the compositional limits of the decomposition. Furthermore, we investigate the magneto-transport properties of shell-ferromagnets obtained by annealing Ni49.8Mn45.1Sn5.1 in a magnetic-field.

Magnetic component of mixing enthalpy for BCC Fe-Cr alloys: ab initio based model

The standard magnetic model in the current CALPHAD modelling is based on the Inden–Hillert–Jarl model and can be used to ferromagnetic and antiferromagnetic alloys. In this work, we demonstrate that this model can also be applied to alloys with more complicated forms of magnetism. The concept of ‘effective magnetic moment’ has been introduced as a measure of the maximum magnetic entropy. To calculate this quantity, it is necessary to know the local magnetic moments on the atoms of the components. A case study on the Fe –Cr system has been performed by Density Functional Theory (DFT) formalism at 0 K. It is shown that the CALPHAD modelling using the concept of effective magnetic moment leads to good agreement with the data of ab-initio modeling of the magnetic contribution to the mixing energy of Fe-Cr alloys.