Effect of non-stoichiometry on wear of ferrite recording heads

VTR ferrite head wear Wragainst CrO2is investigated as a function of δ in single crystals of Ni0.669Fe2.331O4+δ. Two kinds of CrO2tape are used: one with calendered smooth surface(c-tape) and the other with coarse surface(n-tape). Knoop hardness Hkis measured to correlate Wrand Hk. Although Hkincreases with δ, Wrhas a minimum value for the c-tape and a maximum for the n-tape near δ=0. It is concluded from the microscopic observations of the worn surface that the head surface is damaged with brittle fracture in the shape of stripes with a width of about 10 μm due to stress from tape, resulting in wear. It is pointed out that the δ dependence of Wrshould be decided by the nature of the plastic work in Orowan theory. A modified Orowan theory is proposed in order to understand the crystal geometric dependence of the head surface on Wr.