Dependence of popcorn noise on write frequency

In magnetoresistive (MR) heads, domain instability in writer yoke shortly after write operation is detected by reader as a largc transient spike. This type of magnetic instability impairs sector-servo performance in disk drives and is known as popcorn noise (PCN). The noise is induced by the cooling-off of a non-zero magnetostriction (A) yoke after write as well as thermally activated domain wall jumps [l]. Driven by ever increasing areal density and data rate, advanced writer designs employ shorter yoke and less number of coil tums. This demands larger write current and translates into increasing wrile current heating per tum. Eddy current loss at high frequency further aggravates this issue. Therefore, it is pivotal to understand ihe impact of writer heating on popcorn noise over a wide range of write current and frequency. Popcom noise of intcgrated inductivc write/@ valve (SV) read heads was tested on a Guzik spin stand tester. A fxed voltage threshold of 1SOpV was used to detect PCN. Write length for each writelread cycle is 50p Heads with moderate PCN counts were also tested at various write current (Iw=30-60mA) and frequency (10-160MHz). Despite a head-to-head variation, most heads show a PCN peak around 100MHz. The peak PCN count as well as the peak width increases with increasing write current. A typical example is shown in Fig.1.