Surface and bulk magnetic behaviour of sputtered CoCr films

The magnetic hysteresis curve at the surface of RF- and magnetron-sputtered CoCr (81/19 at. %), in the thickness rang of 20-2500 nm, was measured with a rotating-analyser apparatus using the magneto-optic Kerr effect. The Kerr rotation of CoCr films (13-19 at.% Cr) decreases with increasing Cr content, and depends slightly on wavelength, showing a faint minimum between 550 and 600 nm. The surface hysteresis is compared with the bulk hysteresis as measured with a VSM. For RF films the maximum surface coercivity is higher than the bulk coercivity, being 120 and 95 kA m-1 respectively for 80 nm thick films but an abrupt decrease in only the surface coercivity was found at t = 125 nm. The coercivity of magnetron-sputtered CoCr deviates from that of RF-sputtered films. Until a maximum coercivity is reached at » 1 mm, the surface coercivity is about 20% higher, but at »2mm both coercivities decrease strongly. The existence of reversed domains within the main domains of CoCr is proposed, and the reversal mechanism is thought to be one in which the reversed domains grow at the expense of the main domain.