Magnetic enhancement of Co0.2_{0.2}Zn0.8_{0.8}Fe2_2O4_4 spinel oxide by mechanical milling

We report the magnetic properties of mechanically milled Co$_{0.2}$Zn$_{0.8}$Fe$_2$O$_4$ spinel oxide. After 24 hours milling of the bulk sample, the XRD spectra show nanostructure with average particle size $\approx$ 20 nm. The as milled sample shows an enhancement in magnetization and ordering temperature compared to the bulk sample. If the as milled sample is annealed at different temperatures for the same duration, recrystallization process occurs and approaches to the bulk structure on increasing the annealing temperatures. The magnetization of the annealed samples first increases and then decreases. At higher annealing temperature ($\sim$ 1000$^{0}$C) the system shows two coexisting magnetic phases {\it i.e.}, spin glass state and ferrimagnetic state, similar to the as prepared bulk sample. The room temperature M\"{o}ssbauer spectra of the as milled sample, annealed at 300$^{0}$C for different durations (upto 575 hours), suggest that the observed change in magnetic behaviour is strongly related with cations redistribution between tetrahedral (A) and octahedral (O) sites in the spinel structure. Apart from the cation redistribution, we suggest that the enhancement of magnetization and ordering temperature is related with the reduction of B site spin canting and increase of strain induced anisotropic energy during mechanical milling.Comment: 14 pages LaTeX, 10 ps figure

Magnetism in nanoparticles of semiconducting FeSi2

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Mössbauer, magnetic, and electronic-structure studies of YFe\u3csub\u3e12-x\u3c/sub\u3eMo\u3csub\u3ex\u3c/sub\u3e compounds

Mössbauer spectra, magnetization measurements, and self-consistent spin-polarized electronic structures of YFe12-xMox, where x=0.5, 1.0, 2.0, 3.0, and 4.0, are reported. The ternary compounds YFe12-xMox have the crystalline tetragonal ThMn12 structure. Analyses of the Mössbauer spectra show that Mo atoms occupy the 8i Fe sites of the ThMn12 structure, in agreement with previous observations. Room-temperature magnetic and Mössbauer measurements show that the compounds with x≤2.0 are ferromagnetic and with x≥3.0 are paramagnetic. Measurements at 25 K show that all the samples are magnetically ordered. The magnetic hyperfine field is found to decrease with increasing Mo concentration, which is in qualitative agreement with the calculated magnetic moments. The calculated magnetization decreases less rapidly with increasing x than the experimental data. In general the data suggest that with increasing Mo concentration there is an increase of antiferromagnetic coupling among the Fe moments, which leads to cluster-glass or spin-glass-like phenomena. The measured isomer shift relative to α-iron is found to decrease linearly with x

Mössbauer spectroscopy of magnetic minerals in basalt on Earth and Mars

Mossbauer spectroscopy of iron-titanium containing spinel phases is reviewed. New techniques are presented for determination of their composition using room-temperature Mossbauer spectroscopy. An example of thermal alteration processes is described. The speciality of olivine-containing basalt is briefly discussed with regard to its magnetic properties

Optical and magneto-optical properties of Fe 4−x Co x (x=1–3)

We report a systematic study of the electronic, optical, and magneto-optical properties of the Fe4-xCox (x = 1–3) compounds using the full-potential linearized augmented plane waves (FPLAPW) method within the local spin density approximation (LSDA). Pure Fe (x = 0) and Co (x = 4) have also been studied, the latter in hcp as well as bcc structure, to offer a better comparison. A good agreement is obtained between calculated optical conductivity spectra and experimental data. We note that the magneto-optical properties of these compounds are found to be more akin to those of bcc Co (which has MOKE very similar to that of bcc Fe) than to those of hcp Co. This shows strong impact of the environment on the MOKE of these compounds. With respect to the elemental values, the magnetic moments at Fe sites are found to be larger in general, while those at Co sites are almost the same. However, interestingly, despite their larger magnetic moment, the Kerr rotation remains comparable to that of bcc Fe for most of the energy range. The origin of Kerr spectra has been explained in terms of optical transitions