Small-angle magnetisation rotation

An original technique was developed by Konishi et al. (1969) and extended later on by Narita et al. (1980). This method is known as the small-angle magnetisation rotation (SAMR) method a static bias field H and a tensile stress (o) are applied in the direction of the film a small-amplitude ac driven field H = W max sin(wf) is applied perpendicular to H. It is this ac magnetic field that induces a magnetisation rotation, which can be detected as an induced voltage in a sensor coil wound around the film axis. This response is measured as a function of the applied stress, i.e. of the strain-induced anisotropy. An experimental SAMR set-up is illustrated in fig. 5. The sensitivity of this method was 2 x 10-7 (Narita et al. 1980) and even much higher, namely 10-9 (Hernando et al. 1983). 

For those spins further from resonance, the angle 0 becomes greater and the net rotation toward the x-y plane diminishes until, in the limit, 0 becomes 90 . In this case the bulk magnetisation vector simply remains along the -f-z-axis and thus experiences no excitation at all. In other words, the nuclei resonate outside the excitation bandwidth of the pulse. Since an off-resonance vector is driven away from the y-axis during the pulse it also acquires a (frequency dependent) phase difference relative to the on-resonance vector (Fig. 3.6). This is usually small and an approximately linear function of frequency so can be corrected by phase adjustment of the final spectrum (Section 3.2.8). 

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