Surface magnetic excitations

Application of magnetic fluids in ultrasonic non-destructive testing [1-3] opens the real perspectives for automation of the testing methods, based on the surface waves. This report presents the results of investigations aimed at the creation of the transducer of the surface waves for the automated control. The basic attention is drawn to the analysis of the position of the front meniscus of the contact liquid when the surface waves excite through the slot gap. 

For surface-coil excitation, the flip angle a and, consequently, the transverse magnetization Mxy are functions of position R relative to the coil origin. If tR /Tl < 5, then also M, is a function of a and, consequently, of position. Moreover, the spin density Mo can be a function of R. The signal induced in the receiver coil can be written by inserting (9.2.7) into (9.2.2) ... 

The future is exciting for both experiment and theory. There should be many exciting results to emerge from the study of lanthanide surface magnetism. 

Figure 11 (Left) Image of the magnetic excitations in Lao jPbo.jMnOj. (Right) Data plotted in a three-dimensional space defined by two coordinates of momentum in the horizontal plane and the energy vertically. The shaded surface indicates the possible energies and momenta of the scattered neutrons that are accessible in this experiment maximum intensity occurs where this surface intersects the dispersion surface of the spin waves (r.I.u. = reciprocal lattice unit) (data recorded with HET at ISIS).

A method has been worked out for eddy current testing of surfaces and surface cracks or corrosion under dielectric or non-magnetic metal layer of up to 10 mm. The method is based on excitation of eddy currents by a coil with U - type core and information reading by a sensitive gradientometric element located on a axis of symmetry of the core (fig. 1). 

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