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Proximity-induced Rashba spin-orbit interaction in BaMnO $_\text{3}|$ KTaO $_\text{3}$ heterostructure for antiferromagnetic spintronics

This study proposes and validates via DFT calculations a BaMnO $_3$ |KTaO $_3$ heterostructure that successfully induces a strong Rashba spin-orbit interaction in the antiferromagnetic BaMnO $_3$ layer through proximity to KTaO $_3$ , offering a promising pathway for advancing antiferromagnetic spintronics.

Original authors: Vivek Kumar, Nirmal Ganguli

Published 2026-07-27✓ Author reviewed ⓘ

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CC BY 4.0

Original authors: Vivek Kumar, Nirmal Ganguli

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine a world where your computer doesn't just think faster, but thinks smarter by using the tiny, invisible spin of electrons instead of just their electric charge. This is the dream of "spintronics," a field trying to build devices that are faster, smaller, and use less energy than the silicon chips in your phone today. But there's a catch: to make these devices work, scientists need materials that can do two very different things at once. First, they need to be "antiferromagnetic," which is like a team of dancers perfectly synchronized in opposite directions, making the material invisible to outside magnetic interference and incredibly stable. Second, they need a special "twist" called the Rashba effect, where the electrons' paths curve in a way that lets us control their spin with electricity. The problem is, nature rarely gives us materials that are both strong dancers and good at twisting. Most materials are great at one but terrible at the other, leaving engineers stuck trying to build a car with a Ferrari engine but bicycle wheels.

This paper, titled "Proximity-induced Rashba spin-orbit interaction in BaMnO3|KTaO3 heterostructure for antiferromagnetic spintronics," is a clever attempt to solve this puzzle by playing matchmaker. The authors, Vivek Kumar and Nirmal Ganguli, propose building a "heterostructure," which is essentially a microscopic sandwich made of two different oxide materials stacked on top of each other. They take one layer, BaMnO3 (BMO), which is a robust antiferromagnet (a great dancer), and pair it with another layer, KTaO3 (KTO), which is famous for its strong twisting ability (the Rashba effect) but has no magnetism. The big idea is "proximity": just as a shy person might start dancing if they stand next to a confident one, the authors hypothesize that the KTO layer can "teach" the BMO layer how to twist its electrons without losing its magnetic stability. Using powerful computer simulations (specifically Density Functional Theory), they modeled this sandwich to see if the magic would happen.

The results of their simulation suggest that the plan works surprisingly well. When they built their virtual (BaMnO3)2|(KTaO3)3 sandwich, they found that the BMO part kept its strong antiferromagnetic nature, with a magnetic ordering temperature of about 54 Kelvin. More importantly, the BMO layers near the interface began to show a "linear Rashba interaction," a specific type of spin-splitting that is crucial for controlling electron spin. The simulations revealed that the Rashba coefficient for the manganese (Mn) atoms in the BMO layer was approximately 0.10 to 0.114 eVÅ. This is a significant finding because it is about four times larger than what has been estimated for similar interfaces in other materials like LaAlO3|SrTiO3. The authors also noted that while the KTO layer is known for its own strong Rashba effect, the twisting they observed in the BMO layer was a direct result of the proximity to the KTO, effectively inducing a new property in the magnetic material.

However, the story isn't a perfect fairy tale just yet. The authors are careful to point out that their findings come from computer simulations, not a physical experiment in a lab. In their specific model, the interface became electrically conducting when a thin film of BaMnO3 was grown on a thick KTaO3 substrate, ensuring the heterostructure works as expected. Furthermore, while the Rashba effect was strong, it wasn't as massive as in some other exotic materials like MnBi2Te4. However, in those materials, the "twist" comes from the nonmagnetic Bismuth (Bi) rather than the magnetic Manganese (Mn), which makes them less suitable for the specific needs of antiferromagnetic spintronics. In contrast, this work successfully induces a moderate Rashba interaction directly into the magnetic Manganese bands, which is exactly what is needed for this technology. The paper concludes that this BMO|KTO combination offers a promising roadmap, proving that by stacking materials correctly, we can induce the "twist" we need into a robust magnetic material, potentially paving the way for the next generation of ultra-fast, stable electronic devices.

Technical Summary: Proximity-induced Rashba Spin-Orbit Interaction in BaMnO3|KTaO3 Heterostructure

Problem Statement
Antiferromagnetic spintronics holds promise for ultra-fast electronic devices but faces a critical materials challenge: the simultaneous realization of robust antiferromagnetism and moderate-to-strong Rashba-like spin-orbit interaction (SOI). While oxide heterostructures offer a platform to engineer these properties, existing systems often suffer from weak magnetic moments (e.g., in SrIrO3-based structures) or lack magnetic order entirely (e.g., in KTaO3). The authors propose addressing this limitation by designing a heterostructure that utilizes the proximity effect to induce SOI in a robust antiferromagnet.

Methodology
The study employs Density Functional Theory (DFT) calculations using the VASP code to simulate a $(BaMnO_3)_2|(KTaO_3)_3$ heterostructure.

Structural Model: The simulation assumes epitaxial growth of cubic BaMnO3 (BMO) on a KTaO3 (KTO) substrate. The in-plane lattice constant is fixed at 3.988 Å (matching KTO), while the out-of-plane lattice constant is optimized. The supercell consists of two unit cells of BMO and three unit cells of KTO.
Electronic Structure: Calculations utilize the Local Spin Density Approximation (LSDA) with Hubbard- $U$ corrections ( $U_{eff} = 1$ eV for Ta-5d and $3$ eV for Mn-3d states) to account for strong electron-electron correlations. Relativistic spin-orbit interaction (SOI) is included in all electronic and magnetic property calculations.
Magnetic Analysis: Various magnetic configurations (Ferromagnetic, A-type, C-type, and G-type antiferromagnetic) are tested to determine the ground state. Magnetic exchange interactions ( $J_1$ and $J_2$ ) are mapped onto a spin Hamiltonian.
Thermodynamics: The magnetic ordering temperature (Néel temperature) is estimated using Metropolis Monte Carlo simulations on lattice sizes up to $30 \times 30$ , calculating magnetic specific heat to identify phase transitions.
Electrostatic Modeling: A parallel plate capacitor model is used to analyze the electrostatic potential arising from the polar KTO and non-polar BMO layers, predicting charge transfer requirements based on layer thickness.

Key Results

Structural and Magnetic Stability: The cubic phase of BMO within the heterostructure is found to be both statically (elastic tensor) and dynamically (phonon dispersion) stable. The ground state magnetic configuration is identified as C-type antiferromagnetism, which is lower in energy than ferromagnetic, A-type, and G-type arrangements.
Magnetic Properties: The C-type antiferromagnetic state exhibits a significant magnetic moment of approximately 2.776 $\mu_B$ per Mn atom. The estimated magnetic ordering temperature is $\sim$ 54 K, derived from Monte Carlo simulations of the specific heat peak. The system shows a magneto-crystalline easy axis along the (110) direction, with anisotropy enhanced by the proximity to KTO compared to bulk BMO.
Band Alignment and Charge Transfer: The heterostructure displays a Type-I band alignment, where the valence band maximum and conduction band minimum of the smaller bandgap material (BMO) lie within the bandgap of KTO. Electrostatic modeling suggests that while the specific $(BaMnO_3)_2|(KTaO_3)_3$ simulation cell does not host a conducting interface, increasing the KTO thickness beyond 10 unit cells would trigger charge transfer and create a conducting interface.
Proximity-Induced Rashba Interaction:
- While bulk cubic BMO and isolated BMO slabs do not exhibit Rashba splitting, the $(BaMnO_3)_2|(KTaO_3)_3$ heterostructure shows pronounced linear Rashba splitting in the bands near the Fermi level.
- Projected charge density analysis confirms these bands originate primarily from the BMO (Mn-3d and O-2p) orbitals, not the KTO (Ta-5d) orbitals, which reside at higher energies.
- The spin textures of the split bands exhibit helical rotation along isoenergetic contours, characteristic of linear Rashba interaction.
- Fitting the band dispersion to a two-band Rashba model yields linear Rashba coefficients ( $\alpha$ ) of approximately 0.10 eV·Å and 0.114 eV·Å for the relevant valence bands. This value is noted to be roughly four times larger than that estimated for the LaAlO3|SrTiO3 interface.

Significance and Claims
The paper claims to demonstrate a viable roadmap for antiferromagnetic spintronics by combining a robust antiferromagnet (BMO) with a material possessing strong intrinsic SOI (KTO). The primary contribution is the observation of proximity-induced Rashba interaction within the antiferromagnetic Mn-3d bands. The authors assert that this system successfully overcomes the trade-off between magnetic robustness and spin-orbit coupling strength.

The work suggests that the BMO|KTO heterostructure offers a unique combination of substantial antiferromagnetism (with a significant magnetic moment and ordering temperature) and a moderate, tunable Rashba spin-orbit interaction. The authors conclude that this proximity effect provides a promising platform for future research, potentially enabling the manipulation of magnetic domains via spin-orbit torque in antiferromagnetic systems. The study emphasizes that while the Rashba coefficient here is not as high as in some non-magnetic topological systems, its presence in the magnetic Mn-3d bands is unprecedented and directly relevant for antiferromagnetic spintronics applications.

Technical Summary: Proximity-induced Rashba Spin-Orbit Interaction in BaMnO3|KTaO3 Heterostructure

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