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Mössbauer study of “3c” superstructure of the ferrimagnetic Fe7Se8

Abstract Fe7Se8 has been studied by Mossbauer spectroscopy and X-ray diffraction. The crystal structure is found to be a “3c” hexagonal superstructure of the NiAs structure. It is shown that the Mossbauer results obtained at temperatures below 60 K are also consistent with the Okazakis “3c” superstructure model. Abrupt change of quadrupole shifts near 130 K suggests that the spin-rotation transition proceeds abruptly. The iron ions at all three sites are found to be in a highly covalent ferrous state. The Neel temperature is measured to be 447 ± 2 K in fair agreement with the previously reported value. The Debye temperature is also found to be 248 ± 5 K.

Mössbauer study of antiferromagnetic CuFeS2

SummaryMössbauer spectra of a synthesized CuFeS2 sample were taken at various temperatures ranging from liquid-nitrogen temperature to 820°K. Clear six-line magnetic hyperfine patterns were observed even above 700°K, which was the reported upper limit for the existence of six-line pattern for natural chalcopyrites. No appreciable central peak was observed above 600°K. Isomer shift indicates the ferric character of the Fe ion. No appreciable quadrupole splittings were observed. This is consistent with the almost perfect tetrahedral co-ordination of Fe ions. The Néel temperature was determined to be (815±3)°K.RiassuntoSi sono rilevati gli spettri di Mössbauer di un campione sintetizzato di CuFeS2 a diverse temperature varianti da quella dell’azoto liquido fino a 820°K. Si sono osservati anche sopra i 700°K chiare configurazioni ultrafini magnetiche a 6 linee, questa temperatura di 700°K era considerata il limite superiore per l’esistenza di un modello a 6 linee per calcopiriti naturali. Nessun apprezzabile picco centrale è stato osservato sopra i 600°K. Lo spostamento isomerico indica il carattere ferrico dello ione Fe. Non sono state osservate apprezzabili divisioni di quadripolo. Ciò è coerente con la quasi perfetta coordinazione tetraedrica degli ioni Fe. Si è trovato che la temperatura di Néel è (815±3)°K.РезюмеИсследуются Мессбауэровские спектры синтезированнго образца CuFeS2 при различных температурах в области от температуры жидкого азота до 820°K. Были обнаружены ясные системы шести линий магнитной сверхтонкой структуры даже при температуре выще 700°K, которая, как сообшалось, является верхним пределом для существования системы шести линий для природных халькопиритов. Вьше 600°K не было обнаружено заметного центрального пика. Изомерный сдвит указывает на трехвалентный характер иона железа. Не было обнаружено заметного квадрупольного расщепления. Полученный результат согласуется с почти идеальной тетраэдрической конфигурацией ионов железа. Определено, что температура Нееля составляет (815±3)°K.

Mossbauer studies of nanocrystalline Fe/sub 83/B/sub 9/Nb/sub 7/Cu/sub 1/ alloy by flash annealing

Melt-spun Fe/sub 83/B/sub 9/Nb/sub 7/Cu/sub 1/ alloy with ultrathin ribbon has been studied with Mossbauer spectroscopy and X-ray diffraction. The enhanced magnetic property of the flash-annealed alloy was attributed to the reduced /spl alpha/-Fe phase grain size to 6 nm and the higher effective permeability and smaller magnetic core loss at 1 MHz than conventional annealed alloys. The occupied area of the nanocrystalline phase at the optimum 773 K is about 73% whereas that for conventional annealing temperature at 893 K is about 71%. The flash annealing technique was effective in improving the high-frequency soft magnetic property of nanocrystalline Fe/sub 83/B/sub 9/Nb/sub 7/Cu/sub 1/ alloy.

Superexchange interactions in Cu0.5Fe0.5Rh0.5Cr1.5S4

Abstract Cu0.5Fe0.5Rh0.5Cr1.5S4 has been studied by Mossbauer spectroscopy, X-ray diffraction, and magnetization measurement. The crystal is found to have a cubic spinel structure with the lattice constant a 0 = 9.859 ± 0.005 A . The iron ions are in ferric states and occupy the tetrahedral sites. The temperature dependence of both the magnetic hyperfine field and magnetization is explained by the Neel theory of ferromagnetism using three exchange integrals: J Fe-Cr k B = −13.76 K , J Fe-Fe k B = −8.08 K , and J Cr-Cr k B = 8.53 K . Neel temperature and Debye temperature are found to be 288 ± 2 K and 533 ± 5 K, respectively.

Crystallographic and magnetic properties of Fe0.5Cu0.5Cr2SexS4-x

Abstract Fe 0.5 Cu 0.5 Cr 2 Se x S 4− x (0 x ≤ 2) has been studied by Mossbauer spectroscopy and X-ray diffraction. The crystal structure is found to be a cubic spinel and lattice constant a 0 increases linearly with increasing selenium concentration. The iron ions are ferric and occupy the tetrahedral sites. As interatomic distance increases by 1%, Neel temperature and magnetic hyperfine field decrease by 6 and 4%, respectively.

Mössbauer study of Nix(Cu0.5Fe0.5)1−xCr2S4

Abstract Ni x (Cu 0.5 Fe 0.5 ) 1− x Cr 2 S 4 has been studied by Mossbauer spectroscopy and X-ray diffraction. The crystal is found to have a cubic spinel structure and the lattice constant decreases with increasing Ni concentration. The iron ions are in ferric states and occupy the tetrahedral sites. When the nickel concentration at the tetrahedral sites increases from 10 to 30%, magnetic hyperfine field and Neel temperature are found to decrease by 2 and 9%, respectively. As the interatomic distance decreases by 0.4%, Debye temperature increases rapidly by 37%.

Effects of vanadium impurities on the spin-rotation transition of iron selenide “4c” Fe7Se8

Abstract (Fe0.92V0.08)7Se8 has been studied by Mossbauer spectroscopy and X-ray diffraction. The crystal structure is found to be a triclinic superstructure of the NiAs structure. Abrupt change of quadrupole shifts at 123 K suggests that the spin-rotation transition proceeds abruptly in contrast with the gradual transition reported for Fe7Se8 with the same triclinic superstructure. The iron ions at all four sites are found to be in a highly covalent ferrous state. Neel and Debye temperatures are found to be 420 ± 2 K and 232 ± K, respectively.