Thermal Behavior of Magnetoresistive Heads: An Analysis of the Thermal Asperity Problem

It is well known that the resistance of a magnetoresistive (MR) or giant magnetoresistive (GMR) head, and therefore its output, varies as its temperature changes. This causes uncertainty in the interpretation of magnetic output, and this uncertainty becomes more important when an asperity or particle passes by or comes into contact with the slider, causing a voltage transient during read back. The temperature variation during non-contact is caused by changes in the cooling of the air bearing surface as the flying height changes. When contact occurs an even more significant temperature spike, called a ‘thermal asperity’ (or TA), is caused by frictional heating at the contact interface. These temperature fluctuations are analyzed in this paper. Results show that the temperature of the MR read coil is influenced by bias current in read coil, slider materials and flying height (which is sensitive to surface topography). The temperature variation without contact causes MR output signal variations which can be used to characterize surface topography. The flash temperature rise that occurs with asperity contact can be as much as 150 degrees (C) or more at the contact interface, but it lasts less than a microsecond. The magnitude of the TA temperature spike is affected by contact force, sliding velocity, and geometry and properties of slider and disk materials, including surface films.