Focused ion beam modification of non-local magnon-based transport in yttrium iron garnet/platinum heterostructures

Abstract

We study the impact of Ga ion exposure on the local and non-local magnetotransport response in heterostructures of the ferrimagnetic insulator yttrium iron garnet and platinum. In particular, we cut the yttrium iron garnet layer in between two electrically separated wires of platinum using a Ga ion beam, and study the ensuing changes in the magnetoresistive response. We find that the non-local magnetoresistance signal vanishes when the yttrium iron garnet film between the Pt wires is fully cut, although the local spin Hall magnetoresistance signal remains finite. This observation corroborates the notion that pure spin currents carried by magnons are crucial for the non-local magnetotransport effects observed in magnetic insulator/metal nanostructures.Pure spin transport phenomena give access to important magnetic and magnonic properties of magnetic insulators. 1-8 Taking advantage of the spin Hall effect and the inverse spin Hall effect, pure spin currents can be driven into and detected across the interface between a spin Hall active metal and a magnetic insulator. 1,3,[9][10][11] In particular, the spin Hall magnetoresistance (SMR) allows to probe the magnetic sublattice structure of the magnetic insulator. [1][2][3][4]7,8 In addition, non-local experiments in nanoscale structures with several electrically separated metal wires allow to experimentally access the magnon diffusion length in the magnetic insulator. 5,6,10-12 This non-local approach thus enables studies of the properties of magnetic excitations and their diffusion in the ferromagnetic insulator, and holds the potential for faster and more energy-efficient data processing applications. 13,14 While the non-local transport experiments in magnetic insulator/metal heterostructures so far were discussed and modeled in terms of magnon diffusion, a smoking gun proof that magnons indeed are the relevant transport quantum has not been put forward. Moreover, speculations about different mechanisms surfaced recently, suggesting that angular momentum can also be carried by phonons, that couple the lattice to the magnetic system. 15 Additionally, the observation of non-local transport signatures in Pt wires on a paramagnetic substrate cast doubt on the importance of magnons. 16 Furthermore, higher order effects attributed to magnon swasing and a) Electronic mail: richard.schlitz@tu-dresden.de condensation have been observed. [17][18][19][20] In order to ascertain that magnetic excitations indeed are essential for non-local magnetotransport in magnetic insulator/metal heterostructures, it thus appears mandatory to perform a "scratch test", i.e. , to remove the magnetic material in between the metal wires (cf. Fig. 1a)).In this letter we use a focused ion beam (FIB) of Ga ions to alter and remove the yttrium iron garnet (YIG) in between two platinum wires nanopatterned onto the YIG surface. By performing this nano-scale scratch test, we verify that the non-local effects indeed are suppressed when the YIG is removed. Our findings thus corroborate the notion that ma...

Inverse-design magnonic devices

“…The design region has been divided into 10×10 elements, each with a size of 100×100 nm 2 , in which the magnetic material (YIG) is allowed to be entirely removed. This structure can be fabricated using focused ion beam [34,35] or by Ar + ion etching [6,30,36,37] and the further miniaturization is possible. The yellow regions in Fig.…”

“…It is noted that here we just demonstrate the concept and, for simplicity, use a "binary approach" where each region can have two states: 1 (YIG) or 0 (vacuum). But since the complexity of the functionality of an inverse-design device is fundamentally limited by the number of the degrees of freedom [24,25], namely by the design space, the following approaches can be used: (1) The switch from the 2D to 3D matrices [38，39] or the incremental engineering of (2) the thickness of the elements [35,40], (3) the saturation magnetization [40][41][42] or (4) the exchange stiffness of the magnetic material [42]. An external field of 200 mT is applied out-of-plane along the z-axis, and Forward Volume Spin Waves (FVSWs) are investigated (please note that this is not a classical FV magnetostatic wave (FVMSW) in a plane film since here also an exchange energy is taken into account).…”

Spin-Wave Optics in YIG by Ion-Beam Irradiation

“…Magnonic devices are almost exclusively made from Yttrium Iron Garnet (YIG) substrates, having low attenuation that enables propagation over long distances. Lithographic patterning of YIG allows defining some spin-wave optic functions 5 but has technological challenges 6,7 , as etched or milled film edges introduce undesired behaviors 8 . Even a well-controlled YIG patterning technology would be insufficient to replicate the propagation of electromagnetic waves, which propagate in vacuum, and optical devices can be made by patterning a transparent material to an appropriate shape.…”

From Chaotic Spin Dynamics to Non-collinear Spin Textures in YIG Nano-films by Spin Current Injection

“…Such YIG nano-films are of great interest to implement functionalities based on wave interference in magnon spintronic applications [6][7][8][9]. Being electrically insulating, YIG allows to completely disentangle spin and charge current related physics, which makes this material in particular attractive for studies on spin-related transport phenomena [10][11][12][13][14][15][16]. In addition to its appearance in these topical research fields, YIG is since its discovery a great medium to study highly nonlinear spin dynamics.…”