Probe-based Spin Torque Transfer Device for Writing Hard Disks

In magnetic hard disk technology, continued scaling of bit density requires higher coercivity and anisotropy media in order to maintain data retention time. This creates a major challenge for scaling the electromagnet-based write head, which is currently being addressed by heat-assisted magnetic recording (HAMR) technology. In this work, we investigate the use of spin transfer torque point contacts induced by spin-polarized current injected from a nanoscale probe tip across a very narrow gap into magnetic media to change magnetization direction. We present our recent experiment using a functional nanoprobe to substitute the disk writer structure. State-ofthe-art He-ion focused ion beam (FIB) trimming was used to develop a nanoscale magnetic structure on top of a tip as shown in Fig 1(A). The standard Ta(5nm)/CoFeB(1nm)/MgO(0.9nm) on tip side and another Ta(5nm)/CoFeB(1nm)/MgO(0.9nm) stack on media side were deposited via sputter deposition and milled. The IV characteristics are shown in Fig 1(B) and show magnetization switching of the media through MTJ-type probing. The magnetization change of practical medial structures which consist of sub-10-nm L1(0) ordered FePt structures was observed using the fixed layer of the tip as shown in Fig 1(C). This result suggests a completely new approach for hard disk writing and could pave the way to the field of magnetic recording with ultra-small, ultra-high density, and ultra-fast data rate further.