Platinum/yttrium iron garnet inverted structures for spin current transport

Abstract

plane uniaxial magnetic anisotropy with a well-defined easy axis along <001> and a peak-topeak ferromagnetic resonance linewidth of 7.5 Oe at 9.32 GHz, similar to YIG epitaxilly grown on GGG. Both spin Hall magnetoresistance and longitudinal spin Seebeck effects in the inverted bilayers indicate excellent Pt/YIG interface quality. 2Magnetic garnets are important materials that offer unique functionalities in a range of bulk and thin film device applications requiring magnetic insulators. 1,2 Among all magnetic insulators, yttrium iron garnet (Y 3 Fe 5 O 12 or YIG) has been most extensively used in various high-frequency devices such as microwave filters, oscillators, and Faraday rotators 3 due to its attractive attributes including ultra-low intrinsic Gilbert damping constant ( as low as 3  10 -5 ) 4 which is two orders of magnitude smaller than that of ferromagnetic metals, high Curie temperature (T C = 550 K), soft magnetization behavior, large band gap (~ 2.85 eV), 5 and relatively easy synthesis in single crystal form. These conventional applications demand bulk YIG crystals or micron-thick films grown by liquid phase epitaxy. 6 For more recent spintronic studies such as the spin Seebeck effect (SSE) 7 and spin pumping, 8 submicron-or nanometer-thick films are typically grown by pulsed laser deposition (PLD) or sputtering. It has been shown that high-quality YIG films can be epitaxially grown directly on GGG substrates due to the same crystalline structure and a very small lattice mismatch of 0.057%. [9][10][11] To form bilayers, a thin polycrystalline metal layer is typically deposited on top of YIG by sputtering, which results in reasonably good interfaces for spin current transport. 7,8,12 For some studies such as the magnon-mediated current drag, 13,14 sandwiches of metal/YIG/metal are required, in which YIG needs to be both magnetic and electrically insulating. However, high-quality bilayers of the reverse order, i.e. YIG on metal, are very difficult to be fabricated. A main challenge is that the YIG growth requires high temperatures and an oxygen environment 15 which can cause significant inter-diffusion, oxidation of the metal layer, etc. and consequently lead to poor structural and electrical properties in both metal and YIG layers.This letter reports controlled growth of high-quality single crystal YIG thin films ranging from 30 to 80 nm in thickness on a 5 nm thick Pt layer atop Gd 3 Ga 5 O 12 or GGG (110) substrate. Combined with low-temperature growth which suppresses the inter-diffusion, 3 subsequent rapid thermal annealing (RTA) and optimization of other growth parameters result in well-defined magnetism, atomically sharp Pt/YIG interface, and atomically flat YIG surface. In addition, despite the intermediate Pt layer that has a drastically different crystal structure from the garnets, the top YIG layer shows desired structural and magnetic properties as if it were epitaxially grown on GGG (110).5  5 mm 2 of commercial GGG (110) single crystal substrates are first cleaned in ultrasonic baths...

Spin Hall magnetoresistance in antiferromagnet/heavy-metal heterostructures

“…37 The SMR was first experimentally re-ported in Y 3 Fe 5 O 12 (YIG)/Pt hybrid structures 33,34 and theoretically explained by a non-equilibrium proximity effect. 37 The validity of the SMR model has been confirmed for YIG/Pt [33][34][35][38][39][40][41] and other collinear ferrimagnetic insulator/HM systems like YIG/Ta, 38 Fe 3 O 4 /Pt, 34 NiFe 2 O 4 /Pt, 34 and CoFe 2 O 4 /Pt. 42 Recently, the SMR was used to resolve the orientation of non-collinear magnetic sublattices in canted (Gd 3 Fe 5 O 12 ) 43 or spiral (Cu 2 OSeO 3 ) ferrimagnets.…”

Systematic control of strain-induced perpendicular magnetic anisotropy in epitaxial europium and terbium iron garnet thin films

“…3 (c & d) [27]. As described in equations (1) and (2), Hꓕ has a linear relation with the in-plane strain || , and is expected to follow the same behavior as the out-of-plane strain, εꓕ, according to equations (3) and (4). There are two regimes for the effect of lattice mismatch in thin films [28]: for film thickness t below certain critical value tc, the film will be pseudomorphic and the strain is given by = − , while for t > tc, the strain relaxes…”

Spin Hall-induced auto-oscillations in ultrathin YIG grown on Pt

“…The details of the growth of the YIG/Pt bilayer as well as its structural and static magnetic characterization can be found in ref. 20 . The patterning of the bilayer is performed by defining a negative resist etching mask in the shape of a nanowire with two contact pads via a single e-beam lithography step.…”

“…In spite of the significant efforts, the YIG-based spintronics showed a relatively slow progress because of the difficulties associated with the preparation of high-quality nanometer thick YIG films. Only with the recent developments in this field 15 – 20 , the insulator-based spintronic devices became feasible 8 – 11 .…”

“…The magnetic damping in YIG films is closely related to their structural properties 15 – 20 . Therefore, high-quality YIG films are usually grown on Gadolinium Gallium Garnet (GGG) substrates providing the precise lattice matching of the two materials, while utilization of other substrates results in a significant increase of the damping constant 21 .…”