V. R. Reddy

Investigation of the large magnetic moment in nano-sized Cu0.25Co0.25Zn0.5Fe2O4

Using a combination of x-ray diffraction, transmission electron microscopy, room temperature (RT) and in-field M?ssbauer studies and dc magnetization, the structural and magnetic properties of nano-sized Cu0.25Co0.25Zn0.5Fe2O4, prepared by the chemical co-precipitation method, have been studied. Although the crystallite sizes are only of about 40?nm, these samples show a very large magnetic moment at RT. The moment of 81?A?m2?kg?1 obtained in one of the samples is comparable to one of the largest reported values in spinel ferrites as that found in bulk CoFe2O4. This can be explained in terms of the enhancement in the B?B interaction because of the distortion in the octahedral B site due to the presence of the Jahn?Teller cation Cu at this site. The dependence of magnetic properties on the ?-Fe2O3 content has also been investigated.

Phase evolution in F57e/Al multilayers studied through dc magnetization, conversion electron Mössbauer spectroscopy, and transmission electron microscopy

Fe/Al multilayer thin films with an overall atomic concentration ratio of Fe:Al=1:2 have been prepared by ion-beam sputtering. Phase formation and microstructural evolution with thermal annealing have been studied by x-ray reflectivity, cross-sectional transmission electron microscopy, dc magnetization, and conversion electron Mossbauer spectroscopy. These studies show that although the starting composition is Al rich, the intermixing of Fe and Al at the interfaces leads to the formation of a magnetic Fe3Al-like region at the interface. Thus, the magnetic contribution in the as-deposited multilayer structure (MLS) is not only from pure Fe but also from an Fe3Al-like region formed at the interface. On annealing the MLS, a stable nonmagnetic MLS consisting of intermetallic B2 Fe50Al50 separated by thin Al layers is formed. Further annealing only induces better ordering of Fe50Al50 and does not destroy the MLS.

Size-dependent magnetic properties in Cu0.25Co0.25Zn0.5Fe2O4

Cu0.25Co0.25Zn0.5Fe2O4 nanoparticles were prepared by a co-precipitation method and the size was varied by varying annealing temperatures. The cation distribution, estimated using Mössbauer spectroscopy, shows that it is the same for all samples, irrespective of the size. The variation of Curie temperature and saturation magnetization as a function of particle size, studied using d.c. magnetization, clearly indicates that these are a result of finite size scaling effects. The superparamagnetic size limit is estimated to be 8 nm.

Uniaxial anisotropy induced in 57Fe/Co/Al multilayers

The magnetic properties of 57Fe/Co/Al multilayers with 20 and 40 trilayers, deposited on Si (100) substrate using ion beam sputtering, are reported here. X-ray reflectivity and X-ray diffraction studies indicate the formation of good quality films with preferential growth along the (110) direction. Conversion electron Mossbauer spectra show considerable inter-mixing between the layers and the formation of Fe-Al/Fe-Co-Al phases. The samples are extremely soft with coercivities ≤0.48u2009×u2009103u2009A/m, exhibit strong in-plane uniaxial anisotropy and calculations show that they possess a high ferromagnetic resonance frequency of ∼2u2009GHz. The saturation magnetization value of 1.80u2009×u2009106u2009A/m is comparable with that obtained in multilayer samples with much higher content of Co. The combination of magnetic properties in these multilayers thus makes them ideal candidates for high frequency device applications.

Mössbauer effect in tetragonal SrFeO3-δ

SrFeO3-δ is synthesized through solid state reaction. The sample is thoroughly characterized using different techniques. The crystal structure and the nature of magnetic order are established using XRD, neutron diffraction, magnetization and Mossbauer studies.