No abstract

Using vibrating-sample magnetometry, magnetic properties of iron-filled multiwalled carbon nanotubes have been investigated. The field dependence of dc magnetization at high magnetic fields suggests that these tubes behave as a one-dimensional exchange-coupled ferromagnetic system. At 5K, the saturation magnetization (MS) of the nanowires is found to be 85emu∕g, which is much less than the expected bulk value ∼210emu∕g. The observed exchange bias, in spite of the small fraction of γ-Fe in our samples, implies that γ-Fe may not be the only antiferromagnetic component responsible for the exchange bias in these Fe-filled carbon nanotubes. Quantitative study on the temperature dependence of saturation magnetization, remanent magnetization and coercivity has been carried out.

No abstract

Magnetocaloric effect (MCE) in TbCo 2-x Fe x has been studied by dc magnetization measurements.On substituting Fe in TbCo 2 , not only the magnetic transition temperature is tuned to room temperature, but also the operating temperature range for MCE is increased from 50 K for TbCo 2 to 95 K for TbCo 1.9 Fe 0.1 . The maximum magnetic entropy change (-ΔS M ) for TbCo 1.9 Fe 0.1 is found to be 3.7 J kg -1 K -1 for a 5 T field change, making it a promising candidate for magnetic refrigeration near room temperature. The temperature dependent neutron diffraction study shows a structural phase transition (from cubic to rhombohedral phase with lowering of temperature) which is associated with the magnetic phase transition and these transitions broaden on Fe substitution.To investigate the nature of the paramagnetic to ferrimagnetic phase transition, we performed a critical exponent study. From the derived values of critical exponents, we conclude that TbCo 2 belongs to the 3D Heisenberg class with short-range interaction, while on Fe substitution it tends towards mean-field with long-range interaction. The derived values of critical exponents represent the phenomenological universal curve for the field dependence of ΔS M , indicating that TbCo 2 and TbCo 1.9 Fe 0.1 belong to two different universality classes.PACS number(s): 75.30.Sg, 61.05.fm, 75.40.Cx * Electronic mail: smyusuf@barc.gov.in FAX: +91 22 25505151

A new route for the formation of shape-selective CoO nanowires has been developed using a simple microwave (MW) heating method. The reduction of Co(II) ions was done using a new reducing agent alkaline 2,7-dihydroxy naphthalene (2,7-DHN) in cetyltrimethylammonium bromide (CTAB) micellar media.The reaction mixture was irradiated using MW for a total time of 6 min. The process exclusively generates CoO nanowires of different lengths and having diameter y5 ¡ 2 nm to 15 ¡ 2 nm range just by tuning the metal-ion-to-surfactant molar ratios and changing the other reaction parameters. Magnetization measurements indicate that there is no observable coercivity for the short nanowires, but the coercivity increases as the length of the nanowires increases although the magnetic moment values at the maximum applied magnetic field of 2 T decreased with an increase in the length of the nanowires. The synthesized CoO nanowires are found to serve as an effective catalyst for the mineralization of several organic dye molecules in the presence of NaBH 4 in a short reaction time. The process assists the room temperature mineralization of the dyes and provides a cleanup measure of dye contaminated water bodies even in the presence or in the absence of light. The yield of the CoO nanowires with uniform shapes is found to be significantly high (.95%) and the nanowires are stable for more than a month under ambient conditions.The proposed synthesis method is efficient, straightforward, reproducible, and robust. Other than in catalysis, the cobalt oxide nanomaterials can also be applied for making pigments, lithium-ion battery materials, solid state sensors, or as anisotropy source for magnetic recording.