Giant magnetic anisotropy at nanoscale: overcoming the superparamagnetic limit

It has been recently observed for palladium and gold nanoparticles, that the magnetic moment at constant applied field does not change with temperature over the range comprised between 5 and 300 K. These samples with size smaller than 2.5 nm exhibit remanence up to room temperature. The permanent magnetism for so small samples up to so high temperatures has been explained as due to blocking of local magnetic moment by giant magnetic anisotropies. In this report we show, by analysing the anisotropy of thiol capped gold films, that the orbital momentum induced at the surface conduction electrons is crucial to understand the observed giant anisotropy. The orbital motion is driven by localised charge and/or spin through spin orbit interaction, that reaches extremely high values at the surfaces. The induced orbital moment gives rise to an effective field of the order of 103 T that is responsible of the giant anisotropy.Comment: 15 pages, 2 figures, submitted to PR

Synthesis and characterization of FePt/Au core-shell nanoparticles

In this work, the structural and magnetic properties of the gold- coated FePt nanoparticles synthesized from high- temperature solution phase are presented. The amount of gold was optimized to obtain most of the FePt particles coated. The particle diameter increases from 4 to 10 nm as observed by TEM. The magnetic properties are largely affected by the coating. At low temperature, the coercive. field Hc of the coated nanoparticles decreases about three times respect to the uncoated and the blocking temperature reduces to the half. The changes of the magnetic behavior are discussed in terms of the effect of the gold atoms at the FePt core surface

Sources of experimental errors in the observation of nanoscale magnetism

It has been recently reported that some non-magnetic materials in bulk state, exhibit magnetic behavior at the nanscale due to surface and size effects. The experimental observation of these effects is based on the measurement of very small magnetic signals. Thus, some spurious effects that are not critical for bulk materials with large magnetic signals may become important when measuring small signals (typically below 0.0001 emu). Here, we summarize some sources of these small magnetic signals that should be considered when studying this new nanomagnetismComment: 16 pages, 10 figure

Plant Growth-Promoting Microbes from Herbal Vermicompost

Overreliance on chemical pesticides and fertilizers has resulted in problems including safety risks, outbreaks of secondary pests normally held in check by natural enemies, insecticide resistance, environmental contamination, and decrease in biodiversity. The increasing costs and negative effects of pesticides and fertilizers necessitate the idea of biological options of crop protection and production. This includes the use of animal manure, crop residues, microbial inoculum, and composts. They provide natural nutrition, reduce the use of inorganic fertilizers, develop biodiversity, increase soil biological activity, maintain soil physical properties, and improve environmental health