T. M. Crawford
Nov. 16, 2007

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Controlled Magnetostatic Mode Pumping in Patterned Magnetic Thin Films
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We demonstrate the use of spatially confined magnetic field pulses to 
selectively pump magnetostatic standing wave modes in patterned magnetic 
thin films. The presence of these modes is detected via a beating in the 
time domain inductive response from a fast risetime magnetic field pulse. 
The field is created by sending a fast current pulse down a microwave 
waveguide that overlaps a 1 mm long ensemble of patterned magnetic thin 
films. By correctly designing the dimension and position of the waveguide 
with respect to the magnetic elements, we can pump specific higher order 
modes. For example, we observe the n=0 and n=1 modes in a device that pulses 
only the outer half of the element, where the mode index, n, indicates the 
number of nodes in the in-plane magnetization.  For a device that excites 
only the middle one-third of the element, we observe the n=0 and n=2 modes. 
We have even excited a set of even index modes that range from n=2 to n=10 
when the waveguide excites approximately the middle 1/15 (6%) of the element.  
We also observe that the amplitude of the inductive waveforms scales linearly 
over a wide range of pulsed field amplitude. This dependence suggests that 
the relative degree of mode excitation is independent of the driving magnetic 
field, and, therefore, that the higher spatial modes are not weak perturbations 
on top of the uniform mode. Instead, this strong, spatially-selective pumping 
effect is explained in terms of the geometrical coupling of the driving 
in-plane magnetic field to the dynamic magnetization pattern of the spatially 
pumped magnetostatic mode. The existence of these modes in such confined 
geometries, when subjected to fast magnetic field pulses, will likely be a 
factor in write head design for high data rate (>1 Gbit/sec) magnetic recording 
systems.