Subsystem domination influence on magnetization reversal in designed magnetic patterns in ferrimagnetic Tb/Co multilayers

Abstract

Recent results showed that the ferrimagnetic compensation point and other characteristic features of Tb/Co ferrimagnetic multilayers can be tailored by He+ ion bombardment. With appropriate choices of the He+ ion dose, we prepared two types of lattices composed of squares with either Tb or Co domination. The magnetization reversal of the first lattice is similar to that seen in ferromagnetic heterostructures consisting of areas with different switching fields. However, in the second lattice, the creation of domains without accompanying domain walls is possible. These domain patterns are particularly stable because they simultaneously lower the demagnetizing energy and the energy associated with the presence of domain walls (exchange and anisotropy). For both lattices, studies of magnetization reversal show that this process takes place by the propagation of the domain walls. If they are not present at the onset, the reversal starts from the nucleation of reversed domains and it is followed by domain wall propagation. The magnetization reversal process does not depend significantly on the relative sign of the effective magnetization in areas separated by domain walls.

Strong lateral exchange coupling and current-induced switching in single-layer ferrimagnetic films with patterned compensation temperature

“…This confirms the interfacial origin of the coupling effect, which becomes stronger in devices with reduced lateral dimensions. The exchange coupling fields reach values as high as 2.5 T. It should be noted that, in contrast to the lateral exchange coupling, the dipolar coupling mechanism reported previously [30,36] decreases in smaller devices and is therefore not useful for miniaturization of devices. The micromagnetic simulations of the effective coupling field with and without dipolar field are shown in the Supplemental Material [37] (see, also, Refs.…”

“…In this work, we realize a strong lateral coupling based on the exchange interaction in a single magnetic layer. We take inspiration from an approach previously developed for synthetic ferrimagnetic systems consisting of stacked layers of rare-earth transition-metal ferrimagnets with different magnetic compensation temperature (T M ) [25][26][27][28][29][30][31]. This type of multilayer is also known as an exchange spring magnet and includes a compensation wall.…”

“…In such an alloy, the strong intralattice coupling between the transition-metal atoms and the weaker interlattice coupling between the rare-earth and transition metal atoms can be separately tuned by altering the composition [32] or microstructure [33], and through reduction/oxidation reactions [34,35]. Recently, He + irradiation has been used to modify T M in a Co/Tb multilayer in order to create multidomain configurations with dimensions of several μm [30,36]. Here we show that patterning of T M in a single GdCo film by either selective oxidation or He + irradiation leads to strong lateral exchange coupling between regions with different T M .…”

“…A sufficiently high external magnetic field can twist the antiparallel magnetization state to the parallel state [Fig. 1(d)], so reducing the Zeeman energy [26,27,30,36,39]. This switching process is accompanied by the creation of a domain wall (DW) for the Co and Gd moments associated with an energy cost E DW .…”

“…In addition to using oxidation, we can realize lateral exchange coupling using He + irradiation, where the spatial modification of T M is achieved by introducing defects and oxygen atoms into the film [30,31,36,43]. The He + irradiation technique offers a good alternative to patterning using oxidation, with exquisite control over the desired coupling strength by changing the irradiation dose and a smaller achievable feature size of 5 nm [44] (see Supplemental Material [37] for the relevant experimental results).…”