Magnetic Domains without Domain Walls: A Unique Effect of He+ Ion Bombardment in Ferrimagnetic Tb/Co Films

Abstract

We show that it is possible to engineer magnetic multi-domain configurations without domain walls in a prototypical rare earth/transition metal ferrimagnet using keV He + ion bombardment. We additionally shown that these patterns display a particularly stable magnetic configuration due to a deep minimum in the free energy of the system which is caused by flux closure and the corresponding reduction of the magnetostatic part of the total free energy. This is possible because light-ion bombardment differently affects an elements relative contribution to the effective properties of the ferrimagnet. The impact of bombardment is stronger for rare earth elements. Therefore, it is possible to influence the relative contributions of the two magnetic subsystems in a controlled manner. The selection of material system and the use of light-ion bombardment open a route to engineer domain patterns in continuous magnetic films much smaller than what is currently considered possible.

Proximity-induced magnetism in Pt layered with rare-earth–transition-metal ferrimagnetic alloys

“…These compensation points lead to useful phenomena, such as fast domain wall motion [32,33], thermally induced switching [34,35], vanishing skyrmion Hall angles [36], and self-focusing skyrmion racetracks [37], while efficient spin-orbit torque switching around compensation has been observed in studies of RE:TM alloys with bulk perpendicular anisotropy (PMA) [38][39][40][41][42], the onset of which may be controlled by the RE content [43]. Recently, it has also been shown that domain walls and compensation temperatures can be altered with ion bombardment [44].…”

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

“…For tailoring magnetic patterns in magnetic thin film systems three classes of methods are currently known: (1) thermal patterning 9 by a tip of a scanning force microscope, (2) laser patterning [10][11][12] , and (3) patterning by light keV-ions 13,14 . In the present work we will focus on consequences of recent results, where it has been found that domains without domain walls (DWs) can be created in Tb/Co ultra-thin layer systems by bombardment with keV-He + -ions 15 . In the present context, by domains in ferrimagnetic films we understand regions with distinct effective magnetization orientation and by DW we denote the transition region between two such domains with a continuously rotating magnetization of both subsystems [15][16][17] .…”

“…In the present work we will focus on consequences of recent results, where it has been found that domains without domain walls (DWs) can be created in Tb/Co ultra-thin layer systems by bombardment with keV-He + -ions 15 . In the present context, by domains in ferrimagnetic films we understand regions with distinct effective magnetization orientation and by DW we denote the transition region between two such domains with a continuously rotating magnetization of both subsystems [15][16][17] . With these definitions in mind, it is possible to conceive magnetic configurations realizable in ferrimagnetic heterostructures with regions of different subsystem domination.…”

“…Examples of such structures abounded in the literature many years ago. With respect to the position of the interface between distinctly dominated regions these ferrimagnetic heterostructures can be divided in two groups: (i) the interface lies in the sample plane [16][17][18] , (ii) the interface is parallel to the surface normal 15,[19][20][21][22] . In such systems, for magnetic fields high enough to parallelly orient the effective magnetization of the regions with different types, a DW is created on the interface.…”

“…In one preceding work 15 about a ferrimagnetic Tb/Co system, composed of Tb/Co multilayers with sublayers thin enough (t Co , t Tb ≤ 1.5 nm) to render the stacks indistinguishable from alloys [38][39][40][41][42] , IB has been shown to modify the two magnetic subsystems of Co and Tb differently: the bombardment changes the Tb magnetic subsystem much more than that of Co and therefore shifts the magnetic compensation point of the material system. It also has been shown that this finding can be used to design magnetic patterns consisting of areas where the Co magnetic subsystem dominates (Co + ) the effective magnetization with exception of areas where the Tb subsystem dominates (Tb + ).…”