I have no links to such papers. I do not even know if such papers exist.
This was mearly hearsay on another forum (file sharing site forum). Here is a paste of the text.
The guy seems to be acknowledging the problem of older drives which is not now a problem, but then alluding to something else.
With older drives there were variances in the data paths. With newer, tightly packed drives? Sorry, Sam.
It is not just the main beam of the data track that you have to worry about. As the track is recorded some of the magnetic field reaches or bleeds into the magnetic particles outside the edges of the track. These particles will retain several layers of the data that existed in the track. Data recovery experts tweak the read head into this noise outside the track and by analyzing the noise at varying distances from the track, several previous layers of data can be reconstructed. It's not perfect, but it definitely can be done. Most of the time this can be done without opening the drive. There are additional disk control commands that support doing this kind of data recovery built into most modern drives. Companies like OnTrack sell tools to do this kind of recovery.
If you have an old cassette recorder and cheap player you do not mind screwing up, you can demonstrate this, by first recording something you will recognize on a blank cassette, then record over it with something else. Playing the tape normally you only hear the new recording, but if you adjust the head on the throw-away player off the track, you will be able to hear parts of the original recor"