A Model for Mark Size Dependence on Field Emission Voltage in Heat-Assisted Magnetic Probe Recording on CoNi/Pt Multilayers

Abstract

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2-7 V with a duration of 500 ns were applied to a CoNi/Pt multilayered film. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm when the pulse voltage is above a threshold voltage. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. The emission area of our tip-sample system derived from an analytic expression for field emission current is approximately equal to the mark size, and is largely independent of pulse voltage. This emission area is large compared to lateral heat diffusion in the film. Thus higher applied voltages lead to higher peak temperatures in the model of the write process, but the mark diameter remains relatively unchanged.Index Terms-Field emission, high-density recording, prolate spheroidal coordinates, scanning tunneling microscope.

A model of heat transfer in STM-based magnetic recording on CoNi/Pt multilayers

“…The mark size is determined as the full-width half-maximum (FWHM) of the MFM signal. Similar to our previous work [7,8], the written marks are magnetic in nature and the writing is reversible. Fig.…”

“…Nakamura et al [6] demonstrated this writing method with an STM several years ago, and saw a mark size that increased with increasing tip voltage. We have also demonstrated the process previously [7,8], but saw very little dependence of mark size on tip voltage above a certain writing threshold. In this work, we complete the model of heat transfer in a multilayered film structure based on the classical Fourier's equation [9] that quantitatively explains the effect of different substrates in mark size, and mark size dependence on pulse voltage.…”

“…The recording medium in experiments is a CoNi/Pt multilayered film [8]. It consists of 20 repeats of 0.55 nmCo 50 Ni 50 and 0.87 nm-Pt bilayers, yielding a total film thickness of about 28 nm.…”

“…The same techniques as in Ref. [8] were used to measure the perpendicular anisotropy, K u , the saturation magnetization, M S , and the coercivity, H C , of the film at room temperature. We obtained K u ¼ 2:5 Â 10 5 J=m 3 , M S ¼ 3:4 Â 10 5 A=m, and H C ¼ 1:1 Â 10 5 A=m.…”

Application of field emission in prolate-spheroidal coordinate in heat-assisted magnetic probe recording

“…This has the possibility of very high spatial resolution as scanning tunneling microscopy (STM), which shows atomic resolution in surface observation [6][7][8]. Some previous work has been done on the demonstration of the STM-based HAMR process on a perpendicular medium [9][10][11][12], but the theoretical model of the write current has not been published yet. In this work, I demonstrated the recording process using different STM tips and completed the model of the writing current based on the Fowler-Nordheim theory [13].…”