In this work we analyse the formation of sigma phase in AlxCrFeCoNi (x = 0–1.5) alloys. In order to characterise the AlxCrFeCoNi system, we decided to investigate 5 additional samples corresponding ...to the individual phases of alloys for x = 1 and 1.5. They were annealed at 600–1000∘C for 24 h. For each of those five samples scanning electron microscope, SEM, XRD and Mössbauer measurements were performed. The SEM/BSE images allowed identify the number of different phases present in the samples and EDX method gave elemental composition of every phase. The XRD technique helped identify those phases, and thanks to Mössbauer spectroscopy we were able to determine the percentage of each of them. The SEM/EDX measurements also revealed spherical Al precipitations which can be clearly divided into two groups in respect of diameter distribution. The analysis of the Mössbauer spectra revealed magnetically split and a paramagnetic component for phases rich in Cr as well as for a phase rich in Al and Ni. We established that the sigma phase is formed in the phase rich in Cr, and has a secondary character. We also provide the degree of transformation to sigma phase for every sample.
•Separate sample series of AlxFeCrCoNi HEA were fabricated, their properties were compared.•FeCrCoNi-rich fcc phase forms a doublet in Mössbauer spectrum.•σ phase transforms from Cr-rich bcc phase only.•Spinodal decomposition was observed in AlNi-rich bcc phase only.•Mössbauer spectra of AlxFeCrCoNi were decomposed into subspectra of respective phases.
High entropy CrxAlFeCoNi alloys with x = 0, 0.5, 1.0 and 1.5 were synthesized using arc-melting and sintering preparation techniques. Three crystal structures (fcc, bcc and σ) were observed using XRD ...technique, while EDX measurements showed the presence of up to three chemically different phases (FeCr-rich phase with fcc structure, AlNi-rich phase with bcc structure and Cr-rich phase with bcc and/or σ structures). The reasons for the observed phase coexistence were addressed to total energy electronic structure calculations using KKR-CPA method accounting for chemical disorder effects. Such theoretical analysis confirmed that the multi-phase system was energetically more favorable than the single-phase one. Furthermore, DSC measurements allowed to identify two phase transitions in melted samples, unlike sintered ones due to high-temperature nitrogen corrosion. This process turned out to be highly selective, resulting in the formation of the scales consisting of AlnNm–phases at the cost of total Al loss in the HEA alloy.
•Two series of CrxAlFeCoNi HEA were fabricated, their properties were compared.•Two crystalline bcc phases cannot be separated using standard XRD technique.•Bcc-grey and σ phases have very close chemical compositions.•For sintered samples high-temperature nitrogen corrosion was observed.•Highly selective corrosion resulted in AlnNm–phases and Al-depleted HEA.
The structure, hyperfine interactions and magnetic properties of the series of multiferroic Bim+1Ti3Fem−3O3m+3 Aurivillius compounds with m=4–8 were studied using X-ray diffraction, 57Fe Mössbauer ...spectroscopy and vibrating sample magnetometry. Samples were prepared by the conventional solid-state sintering method. Bulk magnetic measurements showed that for m=4 the compound is paramagnetic down to 2K while in the compound with m=5 the antiferromagnetic type transition was observed at 11K. In the case of compounds with m=6–8 much more complex magnetic behavior was found. For these compounds a gradual spin freezing and antiferromagnetic spin glass-like ordering were observed on decreasing temperature. The temperature of spin glass freezing was determined as 260, 280 and 350K for m=6, 7 and 8, respectively. Room-temperature Mössbauer spectra of all the compounds studied confirm their paramagnetic state. However, liquid nitrogen and liquid helium temperature measurements reveal magnetic ordering with a residual paramagnetic phase contribution for the compounds with m=5–8.
•Aurivillius compounds prepared by solid-state sintering.•Coexistence of antiferromagnetic and paramagnetic phases seen by Mössbauer spectra.•Hyperfine interactions parameters of compounds determined.•Antiferromagnetic spin glass-like ordering observed down to 10K.
•Magnetic and specific heat measurements of R11Ni4In9 are reported for the first time.•Magnetic data indicate complex magnetic ordering in the investigated compounds.•Magnetic moments located at ...different sublattices order at different temperatures.•The De Gennes scaling is not fulfilled indicating significant CEF influence.
Magnetic and thermal properties of R11Ni4In9 compounds (R=Pr, Nd, Sm, Gd and Tb) were investigated by means of magnetic and specific heat measurements. These compounds crystallize in orthorhombic Nd11Pd4In9-type crystal structure in which the rare earth atoms occupy five nonequivalent sublattices. For all these compounds except Gd11Ni4In9, the ground state at low temperature is antiferromagnetic. Except Pr11Ni4In9, in temperature dependence of the specific heat a two phase transitions are observed. For compounds with R=Nd and Tb with increasing of the external magnetic field and/or temperature the change to the ferrimagnetic state is observed. Sm11Ni4In9 is an antiferromagnet with small ferromagnetic component. The critical temperature of magnetic ordering does not fulfill the de Gennes scaling which indicates the influence of the crystal electric field in stabilizing the magnetic ordering.
•Experimental and theoretical study of μ-phase Fe–Mo compounds.•Sub lattice-resolved charge-densities and electric field gradients.•Extremely high values of Fe-site charge-densities.
Structural ...(lattice parameters and sub lattice occupancies) and electronic (charge-density and electric field gradient) properties in a series of μ-Fe100−xMox (37.5⩽x⩽44.5) compounds were studied experimentally (X-ray diffraction and Mössbauer spectroscopy) and theoretically (charge and spin self-consistent Korringa–Kohn–Rostoker Green’s function method). The lattice parameters a and c showed a linear increase with x while all five lattice sites were found to be populated by both alloying elements: A(1a) and B(6h) predominantly by Fe atoms whereas C(2c) and D(2c′) by Mo atoms hardly depending on the composition. The population of Fe atoms on the site E(2c″) was ranging between ∼50% at x=37.5 and ∼20% at x=44.5. Fe-site charge-density (isomer shift) and the electric field gradient (quadrupole splitting, QS) were revealed to be characteristic of the lattice site and both of them were almost x-independent. The difference in the charge-density at Fe-atoms at the sites B (the highest value) and those at the sites D (the lowest value) was estimated as high as 0.18e. The average charge-density increases linearly with x. The largest QS-values were those at the sites A and C, while the smallest ones at the site D. The average QS-value was 0.25mm/s.
Heusler alloy Ni48Mn39.5Sn12.5−xAlx (x = 0, 1, 2,3) ribbons were prepared by melt spinning. The cross section of ribbons reveals a typical heterogeneous microstructure consisting of small equi-axed ...and columnar grains. The top and bottom ribbons sides are homogenous in composition but they differ in terms of surface structure. The wheel ribbon side appears smoother and shows some degree of macroscopic organization. On the other hand the free ribbon surface regardless of composition shows a more complex morphology consisting of small equi-axed grains, larger grains forming clusters and conical sub crystal structures. A characteristic twinned plate like microstructure confirming the presence of an increased amount of martensite has been observed for the Ni48Mn39.5Sn9.5Al3 ribbon. The martensitic plates are 70–100 nm in size. The phase shift of 0.5° was detected, while scanning the latter ribbon sample in magnetic force microscope mode, indicating the existence of a magnetic multi-domain structure in this sample.
•Ni–Mn–Sn ribbons show different surface anisotropies between top and bottom side.•The easy magnetization axis of the ribbons lies in the rolling direction.•3Al sample has a characteristic microstructure typical for martensite phase.•The martensitic plates are 70–100 nm in size.•The ribbons show a magnetic multidomain structure.
Martensitic and magnetic transformations in Ni48Mn39.5Sn12.5−xAlx (x=0, 1, 2, 3) Heusler alloy ribbons were investigated. It is demonstrated that both magnetic and structural transformations occur in ...all of the studied samples. It is also shown that substitution of Sn with Al causes the martensitic transformation (MT) and the reverse martensitic transformation (RMT) temperatures to increase to room temperature (ΔTMT=49K; ΔTRMT=43K), whereas the Curie temperature of martensite TCM decreases (ΔT=36K) and the Curie temperature of austenite TCA remains practically insensitive to Al introduction. This then allows to tune TCA and the MT temperature leading to their coincidence at ambient temperature. The austenite phase with the L21 type structure has been identified to exist in all the samples regardless of composition. On the other hand the structure of martensite has been shown to be sensitive to composition. It has been determined as the 10M martensite with (32¯) stacking sequence in Al free samples and the 4O martensite with the stacking periodicity (31¯) in Al containing samples. In addition, the splitting of the field cooling (FC) and the field heating (FH) thermo-magnetic curves at low (50Oe) magnetic field and below the TCM has been attributed to intermartensitic transition. The application of large magnetic field (50kOe) has shown the existence of two distinct ferromagnetic states with a considerable hysteresis loop. The properties of these materials make them promising for magnetocaloric applications.
•Al for Sn substituted Ni–Mn–Sn based ferromagnetic Heusler alloys were produced by melt spinning.•Martensitic, reverse martensitic and intermartensitic transformations were observed, their temperatures and magnitude changed with Al substitution.•Different types of martensite structures were identified depending on Al substitution.•Magnetic studies showed the existence of ferromagnetic and weakly magnetic like state, which was affected by the presence of Al.•Substitution of Al increases the structural transition temperature leading to magneto-structural coupling.
Driven by our code of ethics and our call to reckon with our embeddedness within a white supremacist institution in the US South, the UNC-Chapel Hill School of Social Work re-visioned our approach to ...the MSW curriculum. Using case study methods, we trace our history and on-going work through interviews, document review, and community conversations, centering student voices. Students interviewed spoke about activism prompted by racist events on campus and nationally, and the inadequate response from the administration. Their efforts led to school-wide initiatives including curriculum shifts and accountability and action. The first-year generalist course, Confronting Oppression and Institutional Discrimination was restructured and resituated. Critical Race Theory was infused across the coursework. Two new working groups were created: The Anti-Racism Task Force and Reconciliation Standing Committee. Efforts to address racism and white supremacy in academic spaces require sustained activism to expose how racism is embedded within our institutions. While much work remains in the practice of becoming an antiracist institution, this model can serve as a prototype for others as they work to create programs that are site-specific and universally reflective of the institutional changes we need.
•Epitaxial CoO/Fe(001) bilayers of different Fe oxidation levels were studied.•The exchange bias was investigated as a function of the temperature.•The exchange bias and the coercivity were found to ...depend on the amount of interfacial iron oxide.•The highest exchange bias (HEB=180Oe at 4K) was obtained for the sample with the largest amount of interfacial iron oxide.
The relation between the interface structure and the exchange bias was studied in the epitaxial CoO/Fe(001) bilayers that were grown on MgO(001) using molecular beam epitaxy. Three samples with different interface structures were prepared. The CoO/Fe bilayer, which was prepared using the reactive evaporation of CoO, served as the reference sample. In the other two samples, the CoO/Fe interfaces were modified prior to the CoO growth using either (i) the deposition of a 2Å thick Co layer or (ii) an exposure to molecular oxygen, which resulted in under- and over-oxidized CoO/Fe interfaces, respectively. The actual structures of the resulting interfaces were revealed using conversion electron Mössbauer spectroscopy. For each sample, an iron oxide was found at the interface, and its amount depended on the sample preparation recipe. The exchange bias effect (EB), as a function of the temperature, was experimentally studied in detail using VSM magnetometry. The coercivity showed a distinct peak near the blocking temperature for all samples; however, the peak's location and its width were diverse. The obtained EB values depended on the interface structure. The largest hysteresis loop shift (HEB=180Oe at 4K) was obtained for the sample with the thickest interfacial iron oxide layer.
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