An Experimental Study of Head Instabilities in TMR Sensors for Magnetic Recording Heads with Adaptive Flying Height

We did an experimental study to investigate the effect of the thermal stress due to the heater for adjusting adaptive flying height (AFH) on the readability and instability of tunneling magnetoresistance (TMR) sensors. The slider head consists of a small heater nearby the read/write elements for controlling the clearance between the read/write elements and the recording medium of the magnetic recording system. It is firstly reported that the thermal stress from the AFH heater induces instabilities and caused head degradation. The thermal stress degrades the reader performance by inducing voltage fluctuations and large noise spikes that causes the magnetic recording system having poor bit error rate (BER). The open loop of the transfer curve indicates that the flipping of a synthetic antiferromagnet (SAF) edge magnetization causes these instabilities. The thermal stress reduces the exchange bias field and the energy barrier to flop the SAF edge magnetization. The dispersion and thermal stability of the antiferromagnetic (AFM) layer are the potential root causes of these SAF instabilities because the larger AFM dispersion in these heads gives less net stabilizing field to SAF layers that lowers the energy barrier to flop the SAF edge magnetization. Scanning electron microscope (SEM) images of these weak heads show rough surface and scratches close to the sensor element. The mechanical stress due to these scratches may additionally impact to the stabilizing field of the SAF. key words: adaptive flying height, instabilities, head degradation, AFM dispersion