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1. Effect of Substrate on Spin‐Wave Propagation Properties in Ferrimagnetic Thulium Iron Garnet Thin Films

   https://doi.org/10.1002/aelm.202400398  

   Timalsina, Rupak; Giri, Bharat; Wang, Haohan; Erickson, Adam; Sarin, Suchit; Lamichhane, Suvechhya; Liou, Sy‐Hwang; Shield, Jeffrey E; Xu, Xiaoshan; Laraoui, Abdelghani (July 2024, Advanced Electronic Materials)

   Abstract Rare‐earth iron garnets have distinctive spin‐wave (SW) properties such as low magnetic damping and long SW coherence length making them ideal candidates for magnonics. Among them, thulium iron garnet (TmIG) is a ferrimagnetic insulator with unique magnetic properties including perpendicular magnetic anisotropy (PMA) and topological hall effect at room temperature when grown down to a few nanometers, extending its application to magnon spintronics. Here, the SW propagation properties of TmIG films (thickness of 7–34 nm) grown on GGG and sGGG substrates are studied at room temperature. Magnetic measurements show in‐plane magnetic anisotropy for TmIG films grown on GGG and out‐of‐plane magnetic anisotropy for films grown on sGGG substrates with PMA. SW electrical transmission spectroscopy measurements on TmIG/GGG films unveil magnetostatic surface spin waves (MSSWs) propagating up to 80 µm with a SW group velocity of 2–8 km s⁻¹. Intriguingly, these MSSWs exhibit nonreciprocal propagation, opening new applications in SW functional devices. TmIG films grown on sGGG substrates exhibit forward volume spin waves with a reciprocal propagation behavior up to 32 µm. 

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2. Magneto‐Optical Bi‐Substituted Yttrium and Terbium Iron Garnets for On‐Chip Crystallization via Microheaters

   https://doi.org/10.1002/adom.202400708  

   Hayashi, Kensuke; Dao, Khoi Phuong; Gross, Miela J; Ranno, Luigi; Sia, Jia_Xu Brian; Fakhrul, Takian; Du, Qingyang; Chatterjee, Nilanjan; Hu, Juejun; Ross, Caroline A (August 2024, Advanced Optical Materials)

   Abstract Ferrimagnetic iron garnets enable magnetic and magneto‐optical functionality in silicon photonics and electronics. However, garnets require high‐temperature processing for crystallization which can degrade other devices on the wafer. Here bismuth‐substituted yttrium and terbium iron garnet (Bi‐YIG and Bi‐TbIG) films are demonstrated with good magneto‐optical performance and perpendicular magnetic anisotropy (PMA) crystallized by a microheater built on a Si chip or by rapid thermal annealing. The Bi‐TbIG film crystallizes on Si at 873 K without a seed layer and exhibits good magneto‐optical properties with Faraday rotation (FR) of −1700 deg cm⁻¹. The Bi‐YIG film also crystallizes on Si and fused SiO₂at 873 K without a seed layer. Rapidly cooled films exhibit PMA due to the tensile stress caused by the thermal expansion mismatch with the substrates, increasing the magnetoelastic anisotropy by 4 kJ m⁻³versus slow‐cooled films. Annealing in the air for 15 s using the microheater yields fully crystallized Bi‐TbIG on the Si chip. 

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3. Magneto-optical analysis of magnetic anisotropy in ultrathin Tm3Fe5O12/Pt bilayers

   https://doi.org/10.1063/5.0276945  

   Nunley, T Nathan; Russell, Daniel; Chang, Liang-Juan; Lujan, David; Choe, Jeongheon; Guo, Side; Lee, Shang-Fan; Yang, Fengyuan; Li, Xiaoqin (December 2025, APL Materials)

   Magnetic bilayers consisting of an epitaxially grown ferrimagnetic insulator and a heavy metal layer are attractive for spintronic application because of the opportunity for electric control and readout of spin textures via spin–orbit torque. Here, we investigate ultrathin thulium iron garnet (TmIG)/Pt bilayers for TmIG layer thicknesses of 3, 2.7, and 2.3 nm using a sensitive Sagnac magneto-optical Kerr effect technique. We compare the hysteresis loops from out-of-plane and in-plane applied magnetic fields. The preferred magnetization orientation evolves with the TmIG thickness and the presence of the Pt overlayer. We quantify the evolution of the magnetic anisotropy in these ultrathin films and find a significant change even when the TmIG thickness is varied by less than 1 nm. In these ultrathin films, the presence of a Pt overlayer changes the effective anisotropy field by more than a factor of 2, suggesting that the interfacial anisotropy at the Pt/TmIG interface plays a critical role in this regime. 

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4. Ultra-thin lithium aluminate spinel ferrite films with perpendicular magnetic anisotropy and low damping

   https://doi.org/10.1038/s41467-023-40733-9  

   Zheng, Xin Yu; Channa, Sanyum; Riddiford, Lauren J; Wisser, Jacob J; Mahalingam, Krishnamurthy; Bowers, Cynthia T; McConney, Michael E; N’Diaye, Alpha T; Vailionis, Arturas; Cogulu, Egecan; et al (December 2023, Nature Communications)

   Abstract Ultra-thin films of low damping ferromagnetic insulators with perpendicular magnetic anisotropy have been identified as critical to advancing spin-based electronics by significantly reducing the threshold for current-induced magnetization switching while enabling new types of hybrid structures or devices. Here, we have developed a new class of ultra-thin spinel structure Li_0.5Al_1.0Fe_1.5O₄(LAFO) films on MgGa₂O₄(MGO) substrates with: 1) perpendicular magnetic anisotropy; 2) low magnetic damping and 3) the absence of degraded or magnetic dead layers. These films have been integrated with epitaxial Pt spin source layers to demonstrate record low magnetization switching currents and high spin-orbit torque efficiencies. These LAFO films on MGO thus combine all of the desirable properties of ferromagnetic insulators with perpendicular magnetic anisotropy, opening new possibilities for spin based electronics. 

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5. Atomic order of rare earth ions in a complex oxide: a path to magnetotaxial anisotropy

   https://doi.org/10.1038/s41467-024-49398-4  

   Kaczmarek, Allison C; Rosenberg, Ethan R; Song, Yixuan; Ye, Kevin; Winter, Gavin A; Penn, Aubrey N; Gomez-Bombarelli, Rafael; Beach, Geoffrey_S D; Ross, Caroline A (December 2024, Nature Communications)

   Abstract Complex oxides offer rich magnetic and electronic behavior intimately tied to the composition and arrangement of cations within the structure. Rare earth iron garnet films exhibit an anisotropy along the growth direction which has long been theorized to originate from the ordering of different cations on the same crystallographic site. Here, we directly demonstrate the three-dimensional ordering of rare earth ions in pulsed laser deposited (Eu_xTm_1-x)₃Fe₅O₁₂garnet thin films using both atomically-resolved elemental mapping to visualize cation ordering and X-ray diffraction to detect the resulting order superlattice reflection. We quantify the resulting ordering-induced ‘magnetotaxial’ anisotropy as a function of Eu:Tm ratio using transport measurements, showing an overwhelmingly dominant contribution from magnetotaxial anisotropy that reaches 30 kJ m⁻³for garnets with x = 0.5. Control of cation ordering on inequivalent sites provides a strategy to control matter on the atomic level and to engineer the magnetic properties of complex oxides. 

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