Domain configurations in Co/Pd and L1₀-FePt nanowire arrays with perpendicular magnetic anisotropy

Abstract

Perpendicular magnetic anisotropy [Co/Pd]15 and L10-FePt nanowire arrays of period 63 nm with linewidths 38 nm and 27 nm and film thickness 27 nm and 20 nm respectively were fabricated using a self-assembled PS-b-PDMS diblock copolymer film as a lithographic mask. The wires are predicted to support Néel walls in the Co/Pd and Bloch walls in the FePt. Magnetostatic interactions from nearest neighbor nanowires promote a ground state configuration consisting of alternating up and down magnetization in adjacent wires. This was observed over ∼75% of the Co/Pd wires after ac-demagnetization but was less prevalent in the FePt because the ratio of interaction field to switching field was much smaller. Interactions also led to correlations in the domain wall positions in adjacent Co/Pd nanowires. The reversal process was characterized by nucleation of reverse domains, followed at higher fields by propagation of the domains along the nanowires. These narrow wires provide model system for exploring domain wall structure and dynamics in perpendicular anisotropy systems.

Magnetic reversal and thermal stability of CoFeB perpendicular magnetic tunnel junction arrays patterned by block copolymer lithography

“…The deviation may come from the assumption of Stoner-Wohlfarth reversal or from the switching field distribution of the dots which leads to a range of thermal stability factors within the ensemble. Nevertheless, both estimates generally agree with the values reported previously 24,28 .…”

“…Instead, a self-assembly process, block copolymer (BCP) lithography, is convenient for making dense, large-area arrays. Block copolymers can generate well-ordered periodic morphologies on the scale of over 100 nm to sub-10 nm [18][19][20][21] , and transfer of the self-assembled patterns into magnetic films has been used to form arrays of magnetic wires and dots from a range of materials [22][23][24][25][26][27][28] . However, the ensemble behavior of p-MTJ nanoscale arrays has not been explored.…”

Thermal stability of L10-FePt nanodots patterned by self-assembled block copolymer lithography

“…FePt L1 0 dots were made previously using BCP lithography [34] but the structural and magnetic characteristics were not explored in detail. We recently described patterned line arrays of FePt made using BCP lithography [35], but the process was limited by the roughness of the FePt after annealing. Here we use BCP lithography to make arrays of L1 0 FePt dots and measure the thermal stability from the time-dependent coercivity and the interparticle interactions via the first order reversal curve (FORC) method.…”

Domain Wall Configurations and Interactions in Nanowires With Perpendicular Magnetic Anisotropy

“…Magnetic films with perpendicular magnetic anisotropy (PMA) offer improved performance in DW devices because the DWs can be efficiently translated by spin torque transfer [18,19], resulting in the reduction of the threshold current density by 10 -100 times and higher stability without Walker breakdown [20,21]. The PMA materials studied include heavy metal-ferromagnet-oxide multilayers [22], ferromagnetic superlattices [21] and ordered intermetallic alloys [19,23].…”

“…The PMA materials studied include heavy metal-ferromagnet-oxide multilayers [22], ferromagnetic superlattices [21] and ordered intermetallic alloys [19,23]. Furthermore, heterostructures containing PMA films can exhibit phenomena such as the spin Hall effect seen in heavy metal-ferromagnet-oxide multilayers, which can drive DWs at even lower current densities [24][25][26] facilitating electric control of magnetization.…”