Influence of carbon on spin reorientation processes in Er_{2-x}R_{x}Fe_{14}C (R = Gd, Pr) - Mössbauer and magnetometric studies

The $Er_{2-x}R_{x}Fe_{14}C$ (R=Gd, Pr) polycrystalline compounds have been synthesized and investigated with $\text{}^{57}Fe$ Mössbauer spectroscopy and magnetic measurements. The spin reorientation phenomena were studied extensively by narrow step temperature scanning in the neighborhood of the spin reorientation temperature. Obtained Mössbauer spectra were analyzed using a procedure of simultaneous fitting and the transmission integral approach. Consistent description of Mössbauer spectra were obtained, temperature and composition dependencies of hyperfine interaction parameters and subspectra contributions were derived from fits and the transition temperatures were determined for all the compounds studied. Initial magnetization versus temperature measurements (in zero and non-zero external field) for $Er_{2-x}Gd_{x}Fe_{14}C$ compounds allowed to establish the temperature regions of reorientation, change of magnetization value during the transition process. The results obtained with different methods were analyzed and the spin arrangement diagrams were constructed. Data obtained for $Er_{2-x}Gd_{x}Fe_{14}C$ were compared with those for $Er_{2-x}Gd_{x}Fe_{14}B$ series

Influence of carbon on spin reorientation processes in Er 2-xRxFe14C (R = Gd, Pr) - Mossbauer and magnetometric studies

The Er2¡xRxFe14C (R=Gd, Pr) polycrystalline compounds have been synthesized and investigated with 57Fe Mössbauer spectroscopy and magnetic measurements. The spin reorientation phenomena were studied extensively by narrow step temperature scanning in the neighborhood of the spin reorientation temperature. Obtained Mössbauer spectra were analyzed using a procedure of simultaneous fitting and the transmission integral approach. Consistent description of Mössbauer spectra were obtained, temperature and composition dependencies of hyperfine interaction parameters and subspectra contributions were derived from fits and the transition temperatures were determined for all the compounds studied. Initial magnetization versus temperature measurements (in zero and non-zero external field) for Er2¡xGdxFe14C compounds allowed to establish the temperature regions of reorientation, change of magnetization value during the transition process. The results obtained with different methods were analyzed and the spin arrangement diagrams were constructed. Data obtained for Er2¡xGdxFe14C were compared with those for Er2¡xGdxFe14B series

Фазовый состав и магнитная структура нанокомпозитов FeCoZr—(PbSrNaBi)(ZrTi)O₃

Изучены фазовый состав и магнитные свойства гранулированных нанокомпозитов FeCoZr—(PbSrNaBi)(ZrTi)O₃, синтезированных в кислородсодержащей среде с различным давлением кислорода. Анализ фазового состава выполнялся методами рамановской и ЯГР-спектроскопии, а магнитных свойств – методом вибрационной магнитометрии. Установлена взаимосвязь между условиями синтеза композитов, а также окислением металлических гранул, с одной стороны, и магнитными свойствами нанокомпозитов, с другой. Обнаружена возможность изменения положения порога перколяции и величины магниторезистивного эффекта в материале путём вариации давления кислорода при синтезе.Вивчено фазовий склад та магнетні властивості ґранульованих нанокомпозитів FeCoZr—(PbSrNaBi)(ZrTi)O₃, синтезованих у кисневмісному середовищі з різним тиском кисню. Аналіза фазового складу виконувалася методою Раманової та ЯГР-спектроскопії, а магнетних властивостей – методою вібраційної магнетометрії. Встановлено взаємозв’язок між умовами синтези композитів, а також окисненням металевих ґрануль, з одного боку, та магнетними властивостями нанокомпозитів, з іншого. Виявлено можливість зміни положення порогу перколяції та величини магнеторезистивного ефекту в матеріялі шляхом варіяції тиску кисню при синтезі.Phase composition and magnetic properties of FeCoZr—(PbSrNaBi)(ZrTi)O₃ granular nanocomposites synthesized in oxygen-containing ambient with different values of oxygen pressure are studied by Mössbauer spectroscopy, Raman spectroscopy, and vibrating sample magnetometry. Correlations between the synthesis conditions and oxidation of metallic granules and the magnetic properties of nanocomposites are determined. Possibility to tailor percolation threshold and modify magnetoresistive effect value in a material by varying oxygen pressure in a chamber during synthesis is revealed

Electronic self-doping of Mo-states in A2FeMoO6 (A=Ca, Sr and Ba) half-metallic ferromagnets - a Nuclear Magnetic Resonance study

A systematic study of (A,A')2FeMoO6 (A,A'=Ca, Sr, Ba) ferromagnetic oxides with double perovskite structure has been performed using 95,97Mo and 57Fe NMR spectroscopy. These oxides are isoelectronic but have substantially different Curie temperatures. The NMR analysis provides clear evidence that the magnetic moment at Mo sites is not constant but varies sensitively with the ionic size of the alkaline ions. The 95,97Mo frequency, and thus the electronic charge at Mo ions, is found to be smaller in Ba and Ca than in Sr-based oxides. The charge release from Mo sites is accompanied by an uptake at Fe sites, and thus a self-doping Fe-Mo process is observed. This process is controlled by relevant structural parameters: the Fe-O-Mo bond length and bending. A clear relationship between the Curie temperature and the magnetic moment and thus electron density at Mo sites has been disclosed. The relevance of these findings for the understanding of ferromagnetic coupling in double perovskites is discussed.Comment: 26 pages, 8 figure