Compositionally modulated nanomultilayers, showing the room-temperature Perpendicular Magnetic Anisotropy (PMA) which prefers the magnetization normal to the film plane, have attracted much interest from fundamental aspects as well as technical applications to ultrahigh-density magnetic and magneto-optical(MO) recording media. As a example, very recently, Shin et al. have reported the room-temperature PMA in Ni/Pt nanomultilayers having 7-30Å Ni and 3 Å Pt layer thickness and revealed that the magnetoelastic anisotropy plays a major role in yielding PMA in this system. Moreover, it was observed the reduction of saturation magnetization with decreasing the Ni sublayer thickness($t_{Ni}$) which implies the existence of magnetic dead layers.
In this study, we have investigated magnetic and magneto-optical properties of Ni/Pt nanomultilayers using the measurement of Kerr loops with the low temperature MOKES(Magneto-Optical Kerr & Ellipsometric Spectrometer) to identify the existence of magnetic dead layer. We have prepared Ni/Pt nanomultilayers by dc magnetron sputtering at Ar pressure of 7 mTorr. With maintaining the same number of bilayer repeats of 30 and the thickness of Pt sublayer of 4.5Å, the thickness of the Ni sublayer was varied from 5.2 to 42.2 Å. From the results of Torque magnetometer, VSM(Vibrating Sample Magnetometer) and low temperature MOKES experiments, Ni/Pt nanomultilayers with $t_{Ni}$ ＞ 14Å showed PMA at room temperature as well as low temperatures but those having $t_{Ni}$ ＜ 10Å showed in-plane anisotropy at room temperature but the easy axis reorientation occurred with decreasing temperature. it is necessary to make Ni/Pt nanomultilayers having $t_{Ni}$ ＜ 5Å.
