Mn-based Alloys Research Articles

Multiple magnetic transitions and anomalous magnetocaloric effect in an arc melting TbMn2 compound

Magnetic properties of Mn-base alloys are obviously influenced by Mn-content. In this work, multiple magnetic transitions and anomalous magnetocaloric effect of an arc melting TbMn2 intermetallic compound were measured and discussed. TbMn2 shows paramagnetic properties at room temperature. The small bulge at ∼ 230.3 K suggests the rise of a Griffiths phase. The long-range ferromagnetic ordering is established at TC ∼ 60.0 K. The observed antiferromagnetic transition at TN ∼ 45.0 K is caused by the collapse of Mn moments. At ∼ 20.2 K, an unexpected spin reorientation transition is probably due to the arrangement of the sublattice of rare earth. The field induced metamagnetic transition below TN results in an anomalous magnetocaloric effect.

Establishing universality in entropy change and critical behavior for magnetocaloric effect in Si-substituted Mn50Ni40Sn10 inverse Heusler alloy

Magnetic refrigeration working based on the magnetocaloric effect can be the perfect replacement of the conventional gas compression-based refrigeration technology and reduces its harmful effects on the environment. The boundary between a first-order and a second-order phase transition would be where the perfect magnetocaloric material would be found. Therefore, establishing the sequence of phase transitions clearly is essential for the characterization of other phase change materials and for applied magnetocaloric research. A quantitative fingerprint of second-order thermomagnetic phase transitions is reported here in Si-substituted high content Mn-based inverse Heusler alloy systems, which are found to be crystallized in cubic structures. The second-order nature of the phase transition has been confirmed from the Arrott plot analysis and a correlation between magnetocaloric effect and local exponent is established. Using the Arrott plot, the critical exponents are evaluated employing different techniques such as modified Arrott plot, Kouvel–Fisher method, and critical isotherm. Their values are found to be in great agreement with each other and follow the mean-field model signifying the presence of long-range ordering in the materials. The high value of isothermal magnetic entropy change and the reversibility justifies the suitability of the reported materials in the practical application as magnetic refrigerants.

Improving plasticity by Si-addition-induced coherent nanoprecipitates in Cu–Al–Mn alloy fabricated by laser powder bed fusion

In this paper, the Cu-10.8Al-8.3Mn-0.37Si alloy containing Mn5Si3 phase was obtained by adding Si element to the Cu-10.8Al-8.3Mn alloy. The two alloys were printed by laser powder bed fusion. The changes in the organization and tensile properties of the alloys and the mechanism were investigated. After Si addition, the Mn5Si3 nano phase precipitated in the alloy in addition to the β1 austenite phase. The Mn5Si3 phase was co-lattice with the β1 phase with an average size of 10 nm and was diffusely distributed. Standard tensile experiments showed that the yield strength of the Cu-10.8Al-8.3Mn-0.37Si alloy decreased by 57.7% and the elongation increased by 266% compared to the Cu-10.8Al-8.3Mn alloy, while the tensile strength remained essentially unchanged. The presence of Mn5Si3 phase provided nucleation points for martensite and promoted the generation of stress-induced martensite. Hence the yield strength was reduced. TEM results showed that the β1 phase in the Cu-10.8Al-8.3Mn-0.37Si alloy was fully transformed into stress-induced martensite after deformation, which displayed the transformation induced plasticity effect and hindered the slip of dislocations. Meanwhile, the Mn5Si3 phase was sheared by the stacking faults, which promoted the accumulation of hetero-deformation-induced stress. Therefore, the hardening capacity and plasticity of the Cu-10.8Al-8.3Mn-0.37Si alloy were enhanced. This work provides a new idea for the plasticity enhancement of Cu–Al–Mn-based shape memory alloys achieved by co-lattice nano-precipitated phase strengthening.

Effect of Alloying on the Hydrogen Sorption in Ti–Zr–Mn-Based Alloys. Pt. 1: C14-Type Laves-Phase-Based Alloys

The alloys of the Ti–Zr–Mn system based on the C14-type Laves phase are considered as ones of the most promising materials for safe storage and transportation of hydrogen. These alloys have appropriate parameters for activating the processes of absorption and release of hydrogen, a low cost, and a fairly high cyclic stability. In this work, the microstructure and phase composition of the starting alloys and the crystal structure of the hydrides synthesized from them are studied. Possible ways to reduce the cost of the final products are shown. The fact that changing the method of the alloy fabrication does not significantly affect its hydrogen absorption properties is shown. On the example of the considered alloys, it is shown that, as expected, alloying with an element with a larger atomic radius that forms a stable chemical compound with hydrogen results in an increase in the hydrogen capacity. This is explained by both the increased radius of the tetrahedral interstitial sites, where hydrogen atoms are located after dissolution, and the higher total amount of the element interacting with hydrogen.

High Magnetic Performance in MnGa Nanocomposite Magnets.

In view of their potential applicability in technology fields where magnets are required to operate at higher temperatures, the class of nanocomposite magnets with little or no rare earth (RE) content has been widely researched in the last two decades. Among these nanocomposite magnets, the subclass of magnetic binary systems exhibiting the formation of L10 tetragonal phases is the most illustrious. Some of the most interesting systems are represented by the Mn-based alloys, with addition of Al, Bi, Ga, Ge. Such alloys are interesting as they are less costly than RE magnets and they show promising magnetic properties. The paper tackles the case of MnGa binary alloys with various compositions around the Mn3Ga stoichiometry. Four MnGa magnetic alloys, with Mn content ranging from 70 at% to 75 at% were produced using rapid solidification to form the melt. By combining structural information arising from X-ray diffractometry and transmission electron microscopy with magnetic properties determined by vibrating sample magnetometry, we are able to document the nature and properties of the structural phases formed in the alloys in their as-cast state and upon annealing, the evolution of the phase structure after annealing and its influence on the magnetic behavior of the MnGa alloys. After annealing at 400 °C and 500 °C, MnGa alloys are showing a multiple-phase microstructure, consisting of co-existing crystallites of L10 and D022 tetragonal phase. As a consequence of these structurally and magnetically different phases, co-existing within the microstructure, promising magnetic features are obtained, with both coercive fields and saturation magnetization exceeding values previously reported for both alloys and layers of MnGa.

Current-Induced Magnetization Switching Behavior in Perpendicular Magnetized L10-MnAl/B2-CoGa Bilayer

Rare-earth-free Mn-based binary alloy L10-MnAl with bulk perpendicular magnetic anisotropy (PMA) holds promise for high-performance magnetic random access memory (MRAM) devices driven by spin-orbit torque (SOT). However, the lattice-mismatch issue makes it challenging to place conventional spin current sources, such as heavy metals, between L10-MnAl layers and substrates. In this work, we propose a solution by using the B2-CoGa alloy as the spin current source. The lattice-matching enables high-quality epitaxial growth of 2-nm-thick L10-MnAl on B2-CoGa, and the L10-MnAl exhibits a large PMA constant of 1.04 × 106 J/m3. Subsequently, the considerable spin Hall effect in B2-CoGa enables the achievement of SOT-induced deterministic magnetization switching. Moreover, we quantitatively determine the SOT efficiency in the bilayer. Furthermore, we design an L10-MnAl/B2-CoGa/Co2MnGa structure to achieve field-free magnetic switching. Our results provide valuable insights for achieving high-performance SOT-MRAM devices based on L10-MnAl alloy.

Optimized hydrogen storage properties of Ti–Zr–Mn–VFe-based alloys by orthogonal experiment for upscaled production

Ti–Mn-based hydrogen storage alloys have been widely developed for hydrogen compressors and storage because of their excellent hydrogen storage properties. However, there is still a need to develop a high-capacity hydrogen storage based on low-cost and large-scale preparation. Herein, cheap VFe80 intermetallic alloy is employed to replace the expensive V, and Ti–Zr–Mn–VFe-based alloys ((Ti1-yZry)1+xMn1.88-z(VFe)z, x = 0, 0.05, 0.1, y = 0.05, 0.1, 0.15, z = 0.34, 0.44, 0.54) with mainly C14 Laves phase structure were designed and prepared to optimize the composition by an orthogonal experiment. According to the orthogonal analysis, it is found that the maximum hydrogen storage capacity and hysteresis factor mainly are controlled by the content of VFe80 in the Ti–Zr–Mn–VFe-based alloys. The over-stoichiometry of A-side governs the plateau slope, and the content of Zr decreases hydrogen plateau pressure. The optimal Ti0.9Zr0.1Mn1.44(VFe)0.44 alloy achieves a revisable hydrogen storage capacity of 1.73 wt% with low plateau hysteresis factor (0.49) and plateau slope factor (0.73) at room temperature, the dehydrogenation enthalpy and entropy values respectively are 33.92 kJ/mol and 120.64 J/(mol∙K), which exhibits the best overall hydrogen storage properties. Furthermore, the optimal alloy was successfully produced on a large scale, which provides empirical value for upscaled production of AB2 Laves-phase hydrogen alloys.

Transformation behavior and inverse magnetocaloric effect in Ni45Co5Mn36.7In13.3-xGex melt-spun ribbons

In the present work the influence of Ge doping on crystal structure, microstructure, martensitic transformation (MT) and magnetocaloric effect (MCE) of Heusler-type Ni45Co5Mn36.7In13.3-xGex (x = 0, 2, and 3 at. %) metamagnetic shape memory alloys (MetaMSMAs) have been studied. Melt-spinning was used to prepare ribbons of these alloys since the ribbon shape ensures a high surface-to-volume ratio favoring a high heat exchange rate in a solid-state refrigeration. Furthermore, melt-spinning can induce a specific microstructure and stabilize metastable phases at room temperature. The ribbons were examined by X-ray diffraction at different temperatures, scanning electron microscopy, calorimetry, thermomagnetization, and magnetic field induced adiabatic temperature change measurements carried out across MT. It was found that Ge doping gave rise to enhanced antiferromagnetic interactions, stabilized martensitic phase, increased the MT temperature, causing larger magnetization jumps at MT and making narrower MT hysteresis. The x = 3 ribbon exhibited an inverse MCE at 303 K characterized by the isothermal magnetic entropy change value of |26.9|J/kgK at μ0H = 5 T and an adiabatic temperature change of ǀ1.5ǀ K at μ0H = 1.96 T. These values are comparable with the previously reported data on the Ni–Mn-based metamagnetic shape memory alloys in a bulk form.

Trace Ca alloying enhance simultaneously strength and ductility of squeeze-cast Al-5Cu-0.5Mn-based alloys

The strength-ductility inversion relationship of alloys is a persistent challenge in advanced materials design. Al-Cu series cast aluminum alloys that are considered as an exceptionally high-strength light alloy are not exclusive in structural applications due to their inherently poor plasticity. In this work, we employed a squeeze casting technique and Ca microalloying strategy for microstructure modulation to effectively address this difficulty. The addition of low concentrations of Ca (0.5 wt.% and 1 wt.%) elements to the as-cast Al-5Cu-0.5Mn alloy significantly enhances its plasticity by threefold at room temperature. Unexpectedly, even after T6 treatment, which typically compromises ductility for increased strength, the low-Ca micro-alloyed Al-5Cu-0.5Mn exhibited a further increase in its strength without sacrificing its ductility. The low-Ca addition to the alloy generates an ultrafine eutectic colony with a complex "core-shell" structure, which can serve as a carrier for localized stress transfer, effectively distributing the strain uniformly to more grains. Precipitation hardening of α-Al grains and spheroidization of lamellar ultrafine eutectic phases were simultaneously realized in the low-Ca alloy after T6 heat treatment, which resulted in comparable hardness of α-Al grains and eutectic colonies. The synergistic coordination of external strains through extensive strain-hardening induced by slip line and substantial microcrack generation by ultrafine eutectic colonies is evidenced by a series of in situ characterizations of the low-Ca alloys. Therefore, the uniform spreading deformation due to the transfer of strain-hardening effect and the alternating plastic deformation of α-Al grains and ultrafine eutectic colonies are the critical keys to overcoming the strength-plasticity paradox in low-Ca alloys. This study provides a perspective route for Al-Cu system cast aluminum alloys to be utilized as high-strength and tough structural materials.

Influence of Ge-doping on the collinear and non-collinear antiferromagnetic phases of Mn[formula omitted]Si[formula omitted] alloy

Effect of Ge-doping at the non-magnetic site (Si-site) of the Mn-based binary alloy Mn5Si3 has been explored through temperature-dependent x-ray diffraction, dc-magnetic, and electrical transport measurements. All the doped alloys show D88 type hexagonal structure with space group P63/mcm at room temperature and undergoes two structural distortions, hexagonal (P63/mcm) → orthorhombic (Ccmm) → orthorhombic (Cc2m), on cooling. The magnetic characters of these orthorhombic (Cc2m), orthorhombic (Ccmm), and hexagonal (P63/mcm) phases are non-collinear antiferromagnetic (AFM1), collinear antiferromagnetic (AFM2), and paramagnetic (PM), respectively. Doping of Ge results in a significant increase in the AFM1 to AFM2 transition temperature (TN1). However, the AFM2 to PM transition point remains unchanged. In addition, a reasonable increase in the critical field values of the AFM1 to AFM2 transition via another non-collinear antiferromagnetic phase (AFM1′) with increasing Ge concentration has been observed, indicating the strengthening of AFM1 and AFM1′ phases over the AFM2 phase. Such behaviors make the observation of unusual magnetic properties of undoped Mn5Si3 alloys, like inverted hysteresis loop (IHL) and thermomagnetic irreversibility (TI), more evident for these Ge-doped alloys. Further, this study unfolds the presence of conventional and inverse magnetocaloric effect and they found to decrease with Ge doping. An interesting interplay for positive and negative magnetoresistance has also been observed in all the studied alloys.

Synthesis, Structure, and Magnetic Properties of 2Ni–Al–Mn-Based Alloy

Synthesis, Structure, and Magnetic Properties of 2Ni–Al–Mn-Based Alloy

Tuning phase structure and electrochemical hydrogen storage properties of A5B19-type La–Y–Ni–Mn-based superlattice alloys by partial Al substitution

Rare earth-based superlattice alloys are essential anodes for high-performance nickel-metal hydride (Ni-MH) batteries. This study aimed to improve the overall electrochemical hydrogen storage properties of (La0.33Y0.67)5Ni18.1-xMn0.9Alx alloys by adjusting the Al content. The alloys predominantly consist of the 2H–Pr5Co19 phase, with Al atoms mainly occupying the 12k2 site at the [AB5]-1/[AB5]-2 boundary and subsequently the 12k1 site at the [A2B4]/[AB5]-1 boundary. As a result, a minimum subunit volume difference of 2.08 Å3 is observed at x = 0.6. Therefore, the Al substitution is responsible for the decrease in the dehydriding plateau pressure and the increase in discharge capacity. Among them, the alloy (La0.33Y0.67)5Ni17.5Mn0.9Al0.6 presents a discharge capacity of 361.2 mAh/g, a higher capacity retention S200 of 69.80 %, and better rate performance owning to the enhanced hydrogen diffusion rate through the multi-phase interface. This work demonstrates the potential of the (La0.33Y0.67)5Ni17.5Mn0.9Al0.6 alloy as high-performance Ni-MH battery anode.

Magnetic properties and identification of Griffiths-like phase in Mn2FeSi Heusler antiferromagnet

Materials having low magnetic moments with high spin polarization are promising for spintronic applications. Among these materials, Mn-based Heusler alloys are attractive candidates due to the antiferromagnetic alignment of Mn atoms. Theoretical calculations predict Mn2FeSi to have an inverse Heusler (XA) structure with a magnetic moment of 2 μB/f.u. However, no experimental reports exist on a phase-pure composition of this material. In this study, our first principle calculations demonstrate the effect of various types of disorder on the electronic and magnetic properties of Mn2FeSi. The B2-type disorder seems responsible for forming secondary phases in stoichiometric Mn2FeSi. We verify this by conducting theoretical calculations for different configurations of the atomic disorders permissible in a Heusler phase. We substantiate our theoretical investigation with an experimental study wherein we first stabilize the phase-pure Mn2FeSi in an inverse Heusler structure by substituting Al at the Si site. Amongst the prepared Mn2FeSi1−xAlx (x = 0, 0.1, 0.15), the compositions with x = 0 and 0.15 show a clear presence of a secondary phase, identified as the β − Mn phase with a lattice constant of 6.24 Å. Analysis of the back-scattered electron spectroscopy images and X-ray diffraction patterns confirm the formation of a pure Heusler phase in x = 0.1 composition. Magnetization measurements reveal an antiferromagnetic behavior in all compositions, with a N é el temperature of ∼ 50 K. However, deviation from Curie-Weiss law was observed for x = 0.1, suggesting competing magnetic interactions. Further investigation into the magnetic properties of this composition displays signatures of Griffiths phase, possibly caused by antisite disorder in the compound.

Evaluation of the biocompatibility, antibacterial and anticancer effects of a novel nano-structured Fe–Mn-based biodegradable alloys in-vitro study

Scientific backgroundsDevelopment of nanostructured biodegradable alloys has generated a great deal of interest in the recent years as they offer promising bioactive materials for reconstruction of bony defects following traumatic fractures or surgical excision of tumors. ObjectivesThe aim of the current study was to investigate the biocompatibility of Iron–Manganese -based alloys (Fe–Mn) with addition of copper (Cu), Tungsten (W) and cobalt (Co) to obtain 3 different alloys namely, Fe–Mn–Cu, Fe–Mn–W, and Fe–Mn–Co on normal oral epithelial cell line,and their possible anticancer effect on MG-63: osteosarcoma cell line. Materials and methodsThe sulforhodamine B (SRB) assay was used to assess cell viability percentage of both cell lines after exposure to discs of the proposed experimental alloys. Moreover, the antibacterial effect of such alloys against Escherichia coli (E. coli) was tested using disc diffusion susceptibility (Kirby-Bauer method) and colony suspension method. ResultsThe cell viability percentage of oral epithelial cell line showed a significant increase in all the experimental groups in comparison to the control group. The highest percentage was observed in Fe–Mn–Co group, followed by Fe–Mn–W then Fe–Mn–Cu, at 24 and 72-h intervals, respectively. While the cell viability percentage of osteosarcoma cell line showed significant increase in all the experimental groups at 24-h intervals, it showed a significant drop in all the study groups at 72-h intervals. The lowest percentage was observed in Fe–Mn–Cu group, followed by Fe–Mn–W then Fe–Mn–Co. Moreover, all the examined study groups didn't show any inhibition zones against E. coli reference culture. ConclusionsThe novel nanostructured biodegradable Fe–Mn–Cu, Fe–Mn–W, and Fe–Mn–Co metal alloys exhibit good biocompatibility on oral epithelial cell lines with the enhancement of cell proliferation in a time-dependent manner that favors bone regeneration. On the other hand, all the alloys manifested possible anticancer activity against MG-63: osteosarcoma cell line. Furthermore, our study sheds the light on the importance of Co, W and Cu as promising alloying elements. However, the antibacterial activity of the examined alloys is still questionable. Clinical relevanceThe novel nanostructured biodegradable Fe–Mn–Cu, Fe–Mn–W, and Fe–Mn–Co metal alloys offer promising bioactive materials for reconstruction of bony defects following traumatic fractures or surgical excision of tumors, In addition, they could be excellent alternatives for undegradable or non-resorbable alloys that are commonly used. Moreover, they could be used as beneficial 3D printing materials to obtain patient-specific medical implants that favor bone regeneration in addition to manufacturing of plates and screws suitable for fracture fixation.

Evidence of weak itinerant ferromagnetism and Griffiths like phase in MnFeGe

Realizing the itinerant type of magnetic exchange in Mn-based alloys is quite unusual because of the weak hybridization between Mn-moments and conduction electrons. However, in the current study, we found MnFeGe to exhibit weak itinerant type magnetic character possibly arising due to the hybridization between Mn, Fe atoms with Ge atoms. Here, we present a comprehensive structural and magnetic study on polycrystalline MnFeGe. Rietveld refinement of the XRD pattern confirms that Mn and Fe atoms randomly (atomic disorder) occupy the 2a and 2d sites in MnFeGe. From the magnetic measurements, Curie temperature and saturation moment values are found to be 162 K and 1.58 at 2 K, respectively. The relative low values of Curie temperature, saturation magnetic moment, and a large value of Rhodes–Wohlfarth ratio (∼3.4) indicate the weak itinerant ferromagnetic character of the system. The Takahashi spin fluctuation theory analysis further supports the weak itinerant ferromagnetism in MnFeGe. Besides, we also observed Griffiths phase (GP) like behavior above the Curie temperature, which is attributed to the presence of atomic disorder in the system. The presence of GP is further confirmed by the zero spontaneous magnetization. Our findings demonstrate that MnFeGe is one of the very few Mn-based systems with weak itinerant magnetic behavior.

Enhancing thermoelectric performance of n-type Bi2Te2.7Se0.3 through the incorporation of MnSb2Se4 nanoinclusions

Bi2Te3-based alloys are the state of art thermoelectric materials for near-room temperature applications. However, the figure of merit, ZT, of n-type Bi2Te2.7Se0.3 (BTS) is not large enough to its wide applications, and previous studies seldom involve incorporation of Mn-based alloys in BTS-based composites. Here, we show that through dispersion of transition-metal selenide MnSb2Se4 (MSS) into BTS can simultaneously increase the power factor (PF) and reduce lattice thermal conductivity (κL) greatly. Experimental evidences show that increased PF comes from enhanced thermopower due to energy filtering effect; while the reduced κL originates mainly from intensified phonon scattering by the MSS nanoinclusion and dislocations. As a result, a large ZTmax = 1.23 (at 345 K) and an average ZTave ∼ 1.15 (300 K-473 K) are achieved for BTS/0.50 wt% MSS sample, which is respectively ∼ 48% and ∼ 42% larger than those of pristine BTS. In addition, this sample shows better mechanical properties with its Vickers hardness being increased by 17%. Present results demonstrate that incorporation of transition-metal selenides, such as MSS, is a promising way to improving thermoelectric performance as well as mechanical properties of BTS.

The role of Sn trace addition in the precipitation behavior and strengthening of the wrought Al–Cu–Mn-based alloy

The role of Sn trace addition in the precipitation behavior and strengthening of the wrought Al–Cu–Mn-based alloy

Tunnel magnetoresistance exceeding 100% in magnetic tunnel junctions using Mn-based tetragonal alloy electrodes with perpendicular magnetic anisotropy

We studied MgO barrier magnetic tunnel junctions (MTJs) comprising perpendicularly magnetized MnGa and FeCoB electrodes. In those perpendicular (p-) MTJs, we utilized thin metastable bcc CoMn alloys as an interlayer between MnGa and MgO to enhance the tunnel magnetoresistance (TMR) effect. Moreover, we investigated the effect of a thin Mg interlayer between MnGa and CoMn. Owing to the interlayer engineering, we achieved a TMR ratio over 100%, the highest value observed for p-MTJs with a tetragonal MnGa electrode. Our study contributes to the further development of spintronic devices using p-MTJs with various Mn-based tetragonal alloy electrodes.

Research and application of Ti–Mn-based hydrogen storage alloys

Research and application of Ti–Mn-based hydrogen storage alloys

A machine learning enabled ultra-fine grain design strategy of Mg–Mn-based alloys

Grain size is the critical characteristic of ultra-fine grain Magnesium (Mg), which is a concrete representation of the whole heat deformation procedure. In this paper, a design strategy was proposed to quantitatively investigate the composition and process conditions for the preparation of ultrafine grains. Herein, a dataset of Mg–Mn-based wrought alloys was constructed, and the average grain size was set as the design target. Based on this dataset, five machine learning (ML) algorithms, including the k-nearest neighbor (kNN), support vector machine (SVM), decision tree (DT), random forest (RF), and artificial neural network (ANN), were integrated to conduct in-depth analysis and make predictions. Among these models, the computational accuracy of both the DT classifier and ANN predictor is around 90%. The main factors affecting the formation of ultrafine grains were found by ML, and the interrelationships between the features were quantitatively analyzed as well. Then, four suggested routes with conditions were extracted from the tree models for preparing ultrafine grain Mg alloys. And four new Mg alloys were designed through these routes and taken as experimental validation. After testing, the actual grain sizes are close to the predictions, and the accuracy of the experimental verification exceeds 80%. Compared with conventional “trial and error” design methods, the grain design strategy proposed in this paper brings new thought and good prior guidance for developing high-performance commercial Mg alloys.