Influence of magnitude and direction of static magnetic field applied on a drying drop of a laboratory synthesized water base ferrofluid placed on a plane glass plate is investigated. Like all other multi-component fluid this drop also exhibited familiar coffee ring pattern in absence of field while, this pattern is modulated by applying magnetic field and thickness of the ring modulated by the applied field and thickness of the ring decreases exponentially with increase in field when direction of field is normal to the plane of the substrate. Effect of the field on the evaporation rate and temporal variation of contact angle is also studied. Results are analysed in light of available models. The findings may be useful in applications like ink-jet printing, painting and display devices involving ferrofluids.Comment: 8 pages including 8 figure

Frequency dependant complex magnetic permeability is used to understand RF-microwave behaviour of magnetic nanoparticles in the frequency range 250 MHz to 3 GHz. The stable dispersions of Fe3O4 nanoparticles with mean size varying between 11 to 16 nm are prepared for this purpose. The effect of mean particle size and external static magnetic field over microwave absorption properties of magnetic fluid is studied. It is observed that frequency of ferrimagnetic resonance ( ), frequency of maximum absorption ( ), loss tangent (tan ) and reflection loss ( ) can be controlled by modifying mean particle size and strength of applied external static magnetic field. This kind of study can be useful for radiomicrowave devices like tunable attenuator, EM sheilder, and other applications like Hyperthermia.

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