Natural cilia are hair-like microtubule-based structures that are able to move fluid at low Reynolds number through asymmetric motion. In this paper we follow a biomimetic approach to design artificial cilia lining the inner surface of microfluidic channels with the goal to propel fluid. The artificial cilia consist of polymer films filled with magnetic nanoparticles. The asymmetric, nonreciprocating motion is generated by tuning an external magnetic field. To obtain the magnetic field and associated magnetization local to the cilia we solve the Maxwell equations, from which the magnetic torques can be deduced. To obtain the ciliary motion we solve the dynamic equations of motion which are then fully coupled to the fluid dynamic equations that describe fluid flow around the cilia. By doing so we show that by properly tuning the applied magnetic field, asymmetric ciliary motion can be generated that is able to propel fluid in a microchannel. The results are presented in terms of three dimensionless parameters that fully delineate the asymmetry and cycle time as a function of the relative contribution of elastic, inertial, magnetic and viscous fluid forces.

Soft magnetic films with high saturation magnetization and controllable uniaxial anisotropy are required for future high frequency applications. However, the origin and magnitude of the induced magnetic anisotropy are still a contradictory issue. In this paper we show the influence of the structure and composition of sputtered Fe-Zr-N films upon the coercivity and the induced uniaxial magnetic anisotropy. We have found that the increase of the nitrogen content of the sputtered films leads to a reduction of the grain size and a strong increase of the uniaxial anisotropy. The value of 20 Oe for the anisotropy field combined with a saturation magnetization of 20 kG found in a film with average grain size as low as 10 nm gives a ferromagnetic resonance frequency of 1.8 GHz and a roll-off frequency of 1.2 GHz. Such a film is a promising candidate to be used as an ultra-high frequency inductor.Introduction Soft magnetic materials with high saturation magnetization and controllable uniaxial anisotropy are required for future high frequency inductors as well as for high-density recording heads. Such materials must have a well-controlled domain pattern with the magnetization, in the absence of an external magnetic field, oriented in most of the domains parallel to the direction of the anisotropy axis. The hysteresis loop will be a rectangle in the easy direction (domain wall movement) and a straight line in the hard direction (spin rotation). When an external ac field is applied perpendicular to the easy axis the magnetization oscillates with the field. The permeability in this case is given by the ratio between the saturation magnetization (M S ) and the anisotropy field (H K ). This value can be maintained up to the ferromagnetic resonance (FMR) frequency [1] which is given by f r ¼ 2pg(4pM S H K ) 1/2 , were g is the gyromagnetic constant (2pg ¼ 2.8 MHz/Oe).The magnetic domain pattern can be controlled by reduction of the grain size below the ferromagnetic exchange length (the contribution of the magnetocrystalline anisotropy is averaged out) and by introducing an uniaxial anisotropy. Promising materials for this purpose were found to be FeMN thin films, with the typical M being Ta [2], Cr [3], Zr [4], etc. In the past decade large efforts were spent in optimising the microstructure and composition of these materials in order to get optimal magnetic properties. However, the information about the origin and magnitude of induced uniaxial anisotropy is often contradictory. In this paper we show the influence of the nitrogen content on grain size, coercivity and induced anisotropy in Fe-Zr-N films.

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Using various experimental techniques, the formation and evolution of precipitates, the dilation of the matrix, and the nitrogen uptake and release were investigated in cold-rolled Fe 94 Ni 4 Ti 2 and Fe 93 Ni 4 Cr 3 materials subjected to nitriding in a gaseous mixture of NH 3 ϩ H 2 and to reduction in an H 2 atmosphere at low (300 ЊC) to moderate (600 ЊC) temperatures. Transmission electron microscopy (TEM) revealed that in both alloys the precipitates are thin platelets. In the Ti-containing alloy, the precipitates were also small in the lateral dimensions. The difference in size, aspect ratio of the precipitates, and misfit and coherency on the interface consistently explain the substantial differences in dilation of the matrix and nitrogen uptake for the Ti-and Cr-containing alloys under examination. The results provide evidence for the formation of mixed Fe-Ti-N precipitates (Guinier-Preston (GP) zones) in the early stages of nitriding.