In related embodiments of {TAIL ~ the invention}, at least one recessed region is positioned at {HEAD ~ a magnetic pole} 
In related embodiments of { TAIL ~ the invention } , at least one recessed region is positioned at { HEAD ~ a magnetic pole }
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD