Analysis of Reader-Induced "Skew" Bias in Shingled Magnetic Recording

Among key technologies that support areal density growth, shingled magnetic recording (SMR) can be applied with a conventional magnetic recording head and does not require significant head design or structure changes compared to heat-assisted magnetic recording and microwave-assisted magnetic recording. Shingled writing is also essential for 2-D magnetic recording. In the application of SMR with a conventional head which has a single reader and a symmetrical writer, one would expect equal performance between writing with the inner side and the outer side when the head is at 0° skew angle. However, it is found statistically, with a large quantity of samples, that there is a preference toward writing with either inner or outer side depending on whether the head is an up or down facing head in a drive. Two types of readers with opposite wafer level free layer (FL) and reference layer (RL) canting directions also show opposite preference for the data written by the same heads. Experiments performed suggest that the reader may induce some "skew" bias in SMR application on top of the writer contribution. A hypothesis combining reader FL direction and reader RL canting is proposed to explain the observed phenomena.