Mossbauer study of the Heusler-type Fe2MAl compounds for M = V, Cr, Fe, Co, Ni

The crystal structure and magnetic properties of Fe2MAl compounds for M = V, Cr, Fe, Co and Ni were investigated by X-ray, magnetostatic and Mössbauer effect methods. It was found that the investigated compounds possess not perfectly ordered fcc structure of the L21-type. With increasing number of 3d electrons of M component the transition from the paramagnetic to ferromagnetic behaviour follows. Mössbauer spectra were analysed by a hyperfine field distribution method. They are characterictic of the ferromagnetic phase for M = Fe, Co and Ni and indicated the early observed preference of these atoms for the Fe sites

57Fe Mossbauer study of stilpnomelane and associated chlorite from polish granite pegmatites

This paper reports the results of 57Fe Mössbauer study of stilpnomelane K0.6Fe6(Si8Al)(O,OH)27 .2H2O from Żółkiewka (Lower Silesia, Poland). Stilpnomelane in paragenesis with chlorite, tourmaline, claevelandite and zeolites has been found in granite pegmatites in quarries at Żółkiewka. The samples of naturally weathered stilpnomelane and chlorite from the same fragment of rock were also studied. The Mössbauer spectrum of an untreated sample could be fitted to two Fe2+ doublets and two Fe3+ doublets. The Fe2+ doublets have similar isomer shifts, but they distinctly differ in values of quadrupole splittings. Ferric iron, octahedrally coordinated occurs in three different environments represented by two doublets. The first of them, assigned to combined M1 + M2 positions and the second one assigned to M3 site with parameters IS = 0.36 mm/s and QS = 2.07 mm/s is visible in the spectra up to 880°C. This doublet is characteristic of stilpnomelane and can be regarded as a “fingerprint” of this mineral. After heating at 200°C, the relative content of Fe2+, ΣFe2+/ΣFe, decreases to 0.22 what means a 50% decrease in comparison to the initial value observed in the untreated sample. At about 1000°C, complete breakdown of the stilpnomelane structure takes place and the Mössbauer spectrum consists of two sextets and two ferric doublets. Abnormally high content of Fe2+ in naturally weathered stilpnomelane (0.70) comparing to the untreated sample of stilpnomelane (0.45) indicates that the sample had to be subjected to hydrothermal processes operating locally. Almost the same contents of divalent iron and hyperfine parameters of Fe2+ and Fe3+ doublets in weathered stilpnomelane and associated chlorite suggest that the process of chlorite transformation into stilpnomelane seems to be very probable

The investigations of chondritic meteorites by X-ray diffraction and Mossbauer effect methods

The Mossbauer spectroscopy and X -ray diffraction techniques were used to investigate the mineral and magnetic fractions of two meteorites : carbonaceous chondrite named Allende (CV 3) and ordinary chondrite - El Hammami (H 5). The investigations of a powder mixture of chondrules and matrix show that the meteorites studied contain iron mainly in the silicates, olivine, and pyroxene. The metallic fractions of the El Hammami meteorite contain the ferromagnetic mineral kamacite (bcc iron-nickel alloy). This phase with cubic symmetry was identified by symmetric M ossbauer spectrum with disturbance in relative line intensities. The results suggest that the Allende meteorite does not contain a pure metallic phase

Retaining interest in caring for underserved patients among future medicine subspecialists: Underserved Medicine and Public Health (UMPH) program.

BACKGROUND: Accessing subspecialty care is hard for underserved patients in the U.S. Published curricula in underserved medicine for Internal Medicine residents target future-primary care physicians, with unknown impact on future medicine subspecialists. METHODS: The aim was to retain interest in caring for underserved patients among Internal Medicine residents who plan for subspecialist careers at an urban university hospital. The two-year Underserved Medicine and Public Health (UMPH) program features community-based clinics, evening seminars, reflection assignments and practicum projects for 3–7 Internal Medicine residents per year. All may apply regardless of anticipated career plans after residency. Seven years of graduates were surveyed. Data were analyzed using descriptive statistics. RESULTS: According to respondents, UMPH provided a meaningful forum to discuss important issues in underserved medicine, fostered interest in treating underserved populations and provided a sense of belonging to a community of providers committed to underserved medicine. After residency, 48% of UMPH graduates pursued subspecialty training and 34% practiced hospitalist medicine. 65% of respondents disagreed that “UMPH made me more likely to practice primary care” and 59% agreed “UMPH should target residents pursuing subpecialty careers.” CONCLUSIONS: A curriculum in underserved medicine can retain interest in caring for underserved patients among future-medicine subspecialists. Lessons learned include [1] building relationships with local community health centers and community-practicing physicians was important for success and [2] thoughtful scheduling promoted high resident attendance at program events and avoided detracting from other activities required during residency for subspecialist career paths. We hope Internal Medicine residency programs consider training in underserved medicine for all trainees. Future work should investigate sustainability, whether training results in improved subspecialty access, and whether subspecialists face unique barriers caring for underserved patients. Future curricula should include advocacy skills to target systemic barriers

Crystal order and magnetic properties of Fe2.4V0.6Al alloy studied by magnetostatic and Mössbauer methods

Performed investigations showed that the magnetic properties of the Fe2.4V0.6Al alloy markedly depend on the degree of atomic order of its cubic structure. The atomically disordered alloy with A2 (bcc) type structure exhibits ferromagnetic properties. Its Mössbauer spectra can be described by the hyperfine field distribution connected with various local environments of Fe atoms. Alloys with B2 (sc) and DO3 (fcc) type structure do not exhibit magnetic transition above 4.2 K. High values of the magnetization and its strongly non-linear variation with magnetic field intensity in a wide temperature range suggest the presence of magnetic iron clusters in these alloys. Superparamagnetic relaxation times of the order of 10−9 s and 5 × 10−8 s correspond to the largest magnetic clusters with a magnetic moment of 4 × 103 μB in B2 and 104 μB in DO3-type structure, respectively. Mössbauer spectra of these alloys confirm lack of the magnetic order and also suggest the presence of the Fe magnetic clusters with those relaxation times. It was shown that the increase of atomic order of the crystal structure causes formation of the Fe magnetic clusters and disappearing of the magnetic order

Structure and magnetic order in Fe2+xV1-xAl

We present a detailed structural investigation via neutron diffraction of differently heat treated samples Fe2VAl and Fe2+xV1-xAl. Moreover, the magnetic behaviour of these materials is studied by means of mSR and Mossbauer-experiments. Our structural investigation indicates that quenched Fe2VAl, exhibiting the previously reported "Kondo insulating like" behaviour, is off-stoichiometric (6%) in its Al content. Slowly cooled Fe2VAl is structurally better ordered and stoichiometric, and the microscopic magnetic probes establish long range ferromagnetic order below TC = 13K, consistent with results from bulk experiments. The magnetic state can be modelled as being generated by diluted magnetic ions in a non-magnetic matrix. Quantitatively, the required number of magnetic ions is too large as to be explained by a model of Fe/V site exchange. We discuss the implications of our findings for the ground state properties of Fe2VAl, in particular with respect to the role of crystallographic disorder.Comment: accepted for publication in J. Phys.: Condens. Matte

Mossbauer study of the El Hammami olivine-bronzite meteorite

The phase composition of the El Hammami meteorite was investigated by X-ray, magnetostatic, Mössbauer effect and environmental scanning electron microscopy methods. Performed investigations indicated that this meteorite consists of aluminosilicates, olivine (Mg,Fe)2SiO4, pyroxene (Ca,Mg,Fe)SiO3, kamacite (bcc Fe-Ni alloy) and troilite (FeS). Some inclusions of Ti and Cr were observed by scanning electron microscopy. The concentration of Ni in kamacite was determined by comparison of the Mössabauer spectra of Fe-Ni phase in the meteorite with those for synthetic bcc Fe-Ni alloys (5, 10, 25% Ni)

The crystal structure and magnetic properties of selected fcc FeNi and Fe40Ni40B20 alloys

The crystal structure and magnetic properties of polycrystalline alloys Fe62:5Ni37:5, Fe60Ni40, Fe50Ni50 obtained by arc-melting and Fe40Ni40B20 alloy obtained by melt spinning technique were investigated by X-ray, magnetostatic and Mössbauer effect methods. The X-ray measurements show that Fe40Ni40B20 alloy has a face-centered structure (fcc) which means that boron did not cause an amorphous rendering. The lattice constants for this alloy (a = 3:53 Å) is smaller than for FeNi alloys (a > 3:57 Å) which suggests that boron atoms were built-in in the crystal lattice. The Curie temperature of this alloy is more than 150 K higher in comparison with the of FeNi alloys, but the magnetic moment connected with this alloy is more than 0.17 ¹B/atom smaller than the magnetic moments of FeNi alloys. The shape of hyperfine field distribution for Fe40Ni40B20 is similar to the shape of hyperfine field distribution for the investigated fcc Fe62:5Ni37:5 alloy, but both are different from another investigated hyperfine field distribution of FeNi alloys

Mossbauer investigations and photoemission studies of the Fe 3s spin splitting in some Fe-Ni alloys

The magnetic properties, crystal and electronic structure for Fe1¡xNix (x = 0:30, 0.325, 0.375) alloys and austenitic steel were studied using magnetostatic, Mössbauer effect methods, X-ray di®raction and X-ray photoelectron spectroscopy. The compositions of the investigated Fe{Ni alloys were chosen like that to exist on left, right and in inside of invar range. Two different magnetic moments (low and high) of Fe atom were observed. Measurement results do not show antiferromagnetic order in Fe{Ni alloys