Sound damping in ferrofluids: Magnetically enhanced compressional   viscosity
  The damping of sound waves in magnetized ferrofluids is investigated and shown to be considerably higher than in the non-magnetized case. This fact may be interpreted as a field-enhanced, effective compressional viscosity -- in analogy to the ubiquitous field-enhanced shear viscosity that is known to be the reason for many unusual behavior of ferrofluids under shear. 
Hanns Walter Mueller, Yimin Jiang, Mario Liu