We investigate the effects of Cr off-stoichiometry on the structural, magnetic, thermodynamic, and electrical transport properties of the antiferromagnetic compound CrSb. Single-phase hexagonal NiAs-type structure is stabilized only in the Cr-rich regime, where excess Cr atoms preferentially occupy the interstitial trigonal bipyramidal 2d sites, as confirmed from the x-ray diffraction study. Synchrotron-based x-ray absorption fine-structure measurements reveal a progressive increase in local structural disorder with increasing Cr concentration, particularly within the Cr sublattice. Magnetization measurements show a pronounced low-temperature upturn in susceptibility and nonlinear field-dependent behavior, which can be consistently described by the formation of short-range magnetic clusters associated with interstitial Cr moments embedded in the antiferromagnetic CrSb matrix. Specific-heat measurements indicate a finite electronic density of states at the Fermi level with a nonmonotonic evolution of the Sommerfeld coefficient with Cr content, reflecting the interplay between electronic delocalization and disorder-induced localization. Electrical transport measurements confirm metallic conduction across all compositions and reveal the emergence of an antiferromagnetic gap at low temperatures with increasing Cr concentration. These results demonstrate a strong coupling between off-stoichiometry, local structural disorder, magnetic correlations, and charge transport in Cr1+xSb and establish controlled Cr occupancy as an effective route for tuning magnetic interactions and electronic responses relevant to altermagnetic systems.

Recent studies on thermal annealing of Ni-Mn-based alloys at moderate temperatures (<= 750 K) have led to the discovery of novel functionalities. Understanding the microstructural changes that occur during this process is crucial for optimizing annealing conditions to enhance material properties. Herein, we conduct transmission electron microscopy (TEM) experiments to examine the microstructural evolution and the formation of intermediate states in post-annealed Ni50Mn45In5 alloys subjected to thermal treatment at temperatures ranging from 650 K to 750 K. The diffuse scattering and satellite reflections observed in the diffraction patterns of as-cast Ni50Mn45In5 alloys upon thermal annealing are attributed to local enrichment of In elements, leading to the decomposition of the alloy into an L10-NiMn matrix and L21-Ni2MnIn nanoprecipitates. We further conduct in situ heating TEM observations on thin specimens. While both ex situ and in situ TEM experiments reveal similar trends in the processes of alloy decomposition and nanoprecipitation, the influence of sample thickness and vacuum conditions during in situ heating TEM must be carefully considered. Additionally, we analyze the magnetization curves and magnetic domains of the post-annealed samples to establish a relationship between the microstructural features and the magnetic properties of the dual-phase system, consisting of antiferromagnetic L10-NiMn matrix and ferromagnetic L21-Ni2MnIn nanoprecipitates. Our findings on Ni50Mn45In5 alloys provide insights that can be applied to other Ni-Mn-based alloys and potentially to a broader range of materials, offering a framework for understanding alloy decomposition, nanoprecipitation, and their impact on magnetic properties.

We explore the influence of microstructures on the soft magnetic and mechanical properties of the multi-principal element alloys (MPEAs), (MnFeCoNiCu)100−xAlx (x = 20, 25, 30, 35, 40 at.%). Our investigation reveals that the addition of Al promotes a microstructural change from a coexistence of face-centered cubic (FCC), body-centered tetragonal (BCT), and B2 phases to a single B2 phase. The microstructure is characterized by micron-scale FCC precipitates embedded within the B2 matrix. The (MnFeCoNiCu)75Al25 alloys exhibit high saturation magnetization (MS = 105.5 Am2/kg at T = 100 K), low coercivity (HC = 8.7 A/m), high Curie temperature (TC = 732 K), and high Vickers hardness of 513 HV. Lorentz TEM reveals that the B2 phase is a ferromagnetic phase with a domain wall width of 64 ± 3 nm, and the FCC phase is a non-ferromagnetic phase. We find that the FCC nano-precipitates are coherently interfaced with the B2 matrix. Due to their small size (< 20 nm), they do not act as pinning centers. Our work reveals that the direct correlation of magnetic properties with microstructural characteristics is discussed in light of the structure and phase composition changes observed for different aluminum content, and provides valuable guidance for material optimization.

Materials with significant coupling between magnetism and their crystal structure are prone to exhibit multicaloric effects, which offer a novel approach to addressing the bottlenecks of ecologic solid-state refrigeration by optimizing the interplay of multiple driving fields. Here we uncover the multicaloric properties of Cr2Ge2Te6, establishing ferromagnetic van der Waals (vdW) crystals, famous for their spintronics applications, as a previously unrecognized class of multicaloric materials. By combining magnetization measurements with an ab initio disordered local moment theory, we report, for the first time, pronounced barocaloric and multicaloric effects induced by the application of magnetic fields and hydrostatic pressure around Cr2Ge2Te6’s ferromagnetic phase transition. Our experimental and ab initio analysis quantifies the underlying magnetostructural coupling in this material, which accounts for approximately 25% of the total multicaloric entropy change. Significant multicaloric effects are expected to be found in other vdW ferromagnets with strong magnetostructural coupling.

The shell-ferromagnetic effect originates from the segregation process in off-stoichiometric Ni–Mn-based Heusler.

In this work, the FCC-BCC phase transition in (MnFeCoNi)80Cu20-������������������ (������: Al, Ga) high entropy alloys were investigated on the basis of structural, magnetic, hardness and thermal expansion properties. It is found that the equiatomic MnFeCoNiCu alloy is FCC and exhibits mixed ferromagnetic/anti-ferromagnetic interactions with a Curie temperature, T ������, close to room temperature. However, the BCC structure emerges with increasing amount of Al (10 at%) and Ga (15 at%) with additional ferromagnetic interactions and associated T ������s. It is evidenced that in terms of the valence electron concentration and the average magnetic moment values, the investigated HEAs obey the Slater-Pauling rule in a region close to the Heusler alloys. Additionally, they may exhibit similar physical properties like Invar property with low thermal expansion coefficient with the 3d-transition metal-alloys having same valence electron concentration.

NiMn is a collinear antiferromagnet with high magneto crystalline anisotropy (K_2=-9.7×10^5 J m^-3). Through magnetic annealing of NiMn with excess Ni, strongly pinned magnetic moments emerge due to an imbalance in the distribution of Ni in the antiferromagnetic Mn-sublattices. The results are explained with a model of magnetic-field-biased diffusion, supported by ab initio calculations. Another observation is the oxidation of Mn at the surface, causing an enrichment of Ni in the sub-surface region. This leads to an additional ferromagnetic response appearing in the magnetization measurements, which can be removed by surface polishing.

In this work, the FCC-BCC phase transition in (MnFeCoNi)80Cu20−xZx (Z: Al, Ga) high entropy alloys were investigated on the basis of structural, magnetic, hardness and thermal expansion properties. It is found that the equiatomic MnFeCoNiCu alloy is FCC and exhibits mixed ferromagnetic/anti-ferromagnetic interactions with a Curie temperature, Tc, close to room temperature. However, the BCC structure emerges with increasing amount of Al (10 at%) and Ga (15 at%) with additional ferromagnetic interactions and associated Tcs. It is evidenced that in terms of the valence electron concentration and the average magnetic moment values, the investigated HEAs obey the Slater-Pauling rule in a region close to the Heusler alloys. Additionally, they may exhibit similar physical properties like Invar property with low thermal expansion coefficient with the 3d-transition metal-alloys having same valence electron concentration.

The properties of high-entropy alloys containing five or more elements show systematic evolutions with varying valence-electron concentration. This can allow them to be tailored to carry a particular feature or a property. We have prepared a six-component alloy (MnFeCoNiCu) _75 Al _25 , where MnFeCoNiCu makes up the high-entropy part with e/a=9.0 and the added 25 at. e/a=7.5 . Because the structure becomes ordered, the material partially loses its high-entropy character but acquires a ferromagnetic Heusler-like property with a Curie temperature of 525 K and an average magnetic moment of 0.8 _B . The whole of the system mimics Co _3 Al, which cannot be stabilized under normal conditions.

Annealing the collinear antiferromagnet PdMn with excess Pd in a magnetic field produces strongly pinned magnetic moments in the annealing field direction. This behavior can be understood with the help of the magnetic-field-biased diffusion model. Here, the magnetic field creates an energy difference between the two possible occupations of the antiferromagnetic Mn-sublattices by the Pd-excess atoms. This, mediated by diffusion, leads to an imbalance in the amount of the Pd-excess atoms in these sublattices and, subsequently, to an imbalance in the total magnetization of the sublattices. We investigate this effect's dependence on the annealing field, time, and temperature. The results are then compared to the results of the magnetic-field-biased diffusion model, which gives good agreement.

In this study, we investigate the enhancement of exchange bias in core/shell/shell structures by synthesizing single inverted core/shell (Co-oxide/Co) and core/shell/shell (Co-oxide/Co/Co-oxide) nanostructures through a two-step reduction and oxidation method. We evaluate the magnetic properties of the structures and study the effect of shell thickness on the exchange bias by synthesizing various shell thicknesses of Co-oxide/Co/Co-oxide nanostructures. The extra exchange coupling formed at the shell-shell interface in the core/shell/shell structure leads to a remarkable increase in the coercivity and the strength of the exchange bias by three and four orders, respectively. The strongest exchange bias is achieved for the sample comprising the thinnest outer Co-oxide shell. Despite the general declining trend of the exchange bias with Co-oxide shell thickness, we also observe a nonmonotonic behavior in which the exchange bias oscillates slightly as the shell thickness increases. This phenomenon is ascribed to the dependence of the antiferromagnetic outer shell thickness variation at the expense of the simultaneous opposite variation in the ferromagnetic inner shell.

Ni50Mn45Sn05 heated above 600 K decomposes into ferromagnetic Ni2MnSn precipitates in an antiferromagnetic NiMn matrix. If an external magnetic field is applied during annealing, magnetic hysteresis curves with high coercive fields of up to 5 T can be achieved. The origin of this hysteresis has been attributed to the coupling of the antiferromagnetic matrix with the ferromagnetic precipitates, whose location and morphology were not known. To close this knowledge gap, four samples with varying annealing treatments were investigated using switching magnetization magnetic force microscopy. One sample was additionally analyzed with transmission electron microscopy and atom probe tomography. The decomposition type is identified to be a cellular precipitation starting at grain boundaries and growing into the grains. This leads to a multilayer thin film like lamellar structure with a lamella thickness in the nm range. Our results provide a basis for understanding the magnetic interactions, which lead to the magnetic hysteresis with ultra high coercivity.

NiMn is a collinear antiferromagnet with high magneto crystalline anisotropy ($K_2=-9.7\times10^5\;\text{J m}^{-3}$). Through magnetic annealing of NiMn with excess Ni, strongly pinned magnetic moments emerge due to an imbalance in the distribution of Ni in the antiferromagnetic Mn-sublattices. The results are explained with a model of magnetic-field-biased diffusion, supported by ab initio calculations. Another observation is the oxidation of Mn at the surface, causing an enrichment of Ni in the sub-surface region. This leads to an additional ferromagnetic response appearing in the magnetization measurements, which can be removed by surface polishing.

The equiatomic face-centered-cubic (fcc) high-entropy alloy CrMnFeCoNi has a valence electron concentra-tion of 8 electrons per atom, equivalent to that of Fe. Its ground-state properties are similar to that of fcc-Fe and exhibits the anti-Invar effect at finite temperatures. It additionally exhibits various magnetic interactions at low temperatures which are not fully understood. To resolve this, we prepare and investigate the magnetic and structural properties of off-equiatomic Cr20+xMn20Fe20Co20Ni20-x high-entropy alloys with 0 x 20 at.% by making use of the composition-dependent transformation from the fcc to the a phase with increasing x. We employ x-ray diffraction, scanning electron microscopy, magnetization, and microhardness studies. The results suggest that these alloys order antiferromagnetically around 75-90 K before entering into a spin-frozen state below 40 K.

By considering the valence-electron concentration of 3d transition-metal alloys and compounds, we develop 3d high-entropy alloy Mn12.1Fe34.2Co33.5Ni12.3Cu7.9 with 8.7 electrons per atom, which is identical to that of Fe65Ni35 Invar. We carry out x-ray diffraction, scanning electron microscopy, magnetization, thermal expansion, and elastic modulus measurements, by which we show that the HEA alloy indeed carries Invar properties. This is evidenced particularly by the observed spontaneous volume magnetostriction and the lattice softening covering a broad temperature-range around the ferromagnetic Curie temperature.

Fe doping in Ni2Mn1.5In0.5 results in suppression of the martensitic phase via two contrasting routes. In Ni2Mn1.5 - xFexIn0.5, the martensitic phase is converted to a strain glassy phase, while in Ni2 - yFeyMn1.5In0.5, a cubic ferromagnetic phase results at the expense of the martensite. Careful studies of magnetic and structural properties reveal the presence of the impurity gamma-(Fe,Ni) phase as the reason for the emergence of non-ergodic strain glassy phase when Fe is sought to be doped at Y/Z (Mn) sites of X(2)YZ Heusler alloy. Whereas attempts to dope Fe in the X (Ni) sublattice result in an A2 type antisite disorder that promotes a ferromagnetic ground state.

Ni-Co-Mn-In Heusler-based compounds are interesting for their magnetocaloric properties and have been widely investigated for this purpose. For Co compositions more than 5 at% in (Ni100-xCox)(50)Mn25+yIn25-y the material is no longer single phase, and for y < 25, shell-ferromagnetic precipitation occurs. Our study is twofold: First we study here the shell-ferromagnetic properties of these systems and show that their ferromagnetic exchange can be strengthened by introducing Co into the precipitate. Second, we further show that both the multiphase character and shell-ferromagnetic precipitation have strong implications on the magnetocaloric properties.

It has already been theoretically shown that sandwich-type structures prepared by stacking metal nanoparticles in two graphene layers would have exceptional optical and electrical properties for practical applications. These sandwich structures designed by band gap engineering could lead to materials capable of being developed to meet industrial demands. In order to confirm this theoretical approach, copper nanoparticle (CuNP) islands decorated in sandwich-type single-layer graphene (SLG) have been designed and used as a non-enzymatic sensor platform for the first time. Firstly, SLG has been synthesized on copper foil using a chemical vapor deposition technique and transferred onto a fluorine-doped tin oxide surface. Next, CuNPs on this SLG have been prepared using an inert-gas condensation method based on DC magnetron sputtering. A sensor platform based on the sandwich-type hetero-structure (SLG/CuNP/SLG) has been constructed by transferring another single layer of graphene onto the prepared CuNP-decorated graphene layer. In this way, a unique sandwich structure has been obtained for further applications by stacking nanoparticles with high stability, controlled size and regular particle distribution between impurity-free, large-area single layers of graphene. The sensor properties of this sandwich structure to the saccharides have been compared with those of the single-layer sensor platform (CuNP/SLG). In accordance with the theoretical studies in the literature, it has been found that the sandwich structure greatly improves sensor properties such as limit of detection, stability and response time. More importantly, it was determined that the sandwich structure acts as a shielding layer, protecting nanoparticles from electrochemical/optical and other environmental conditions.

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.

Mn-based antiperovskite compounds in the form Mn(3)AX, where A is a main group element and X is C or N, undergo magnetostructural transitions with which these materials acquire magnetocaloric, giant magnetoresistance, and spin-transport properties, which can be modified or tailored by manipulating the compositions of numerous compounds. This enables closer investigations and better understandings of the underlying principles governing these properties. Mn3-xNixGaC, which is a derivative of the prototype Mn3GaC antiperovskite, would normally be expected to form a cubic structure with a homogeneous composition. Contrary to this, we find that the addition of Ni leads to a heterogenous compound consisting of an antiperovskite part and a Ni2MnGa Heusler insertions. The system shows kinetic arrest features, which we study as a function of Ni composition using the techniques of x-ray diffraction, magnetization, and neutron diffraction under a magnetic field.