Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRashba-type Dzyaloshinskii-Moriya interaction, perpendicular magnetic anisotropy and skyrmion states at 2D materials/Co interfaces
172
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report a significant Dzyaloshinskii-Moriya interaction (DMI) and perpendicular magnetic anisotropy (PMA) at interfaces comprising hexagonal boron nitride (h-BN) and Co. By comparing the behavior of these phenomena at graphene/Co and h-BN/Co interfaces, it is found that the DMI in latter increases as a function of Co thickness and beyond three monolayers stabilizes with one order of magnitude larger values compared to those at graphene/Co, where the DMI shows opposite decreasing behavior. At the same time, the PMA for both systems shows similar trends with larger values for graphene/Co and no significant variations for all thickness ranges of Co. Furthermore, using micromagnetic simulations we demonstrate that such significant DMI and PMA values remaining stable over large range of Co thickness give rise to formation of skyrmions with small applied external fields in the range of 200-250 mT up to 100 K temperatures. These findings open up further possibilities towards integrating two-dimensional (2D) materials in spin-orbitronics devices.
rate research
Read More
We report on the study of both perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interaction (DMI) at an oxide/ferromagnetic metal (FM) interface, i.e. BaTiO3 (BTO)/CoFeB. Thanks to the functional properties of the BTO film and the capability to precisely control its growth, we are able to distinguish the dominant role of the oxide termination (TiO2 vs BaO), from the moderate effect of ferroelectric polarization in the BTO film, on the PMA and DMI at the oxide/FM interface. We find that the interfacial magnetic anisotropy energy of the BaO-BTO/CoFeB structure is two times larger than that of the TiO2-BTO/CoFeB, while the DMI of the TiO2-BTO/CoFeB interface is larger. We explain the observed phenomena by first-principles calculations, which ascribe them to the different electronic states around the Fermi level at the oxide/ferromagnetic metal interfaces and the different spin-flip processes. This study paves the way for further investigation of the PMA and DMI at various oxide/FM structures and thus their applications in the promising field of energy-efficient devices.
The possibility of utilizing the rich spin-dependent properties of graphene has attracted great attention in pursuit of spintronics advances. The promise of high-speed and low-energy consumption devices motivates a search for layered structures that stabilize chiral spin textures such as topologically protected skyrmions. Here we demonstrate that chiral spin textures are induced at graphene/ferromagnetic metal interfaces. This is unexpected because graphene is a weak spin-orbit coupling material and is generally not expected to induce sufficient Dzyaloshinskii-Moriya interaction to affect magnetic chirality. We demonstrate that graphene induces a new type of Dzyaloshinskii-Moriya interaction due to a Rashba effect. First-principles calculations and experiments using spin-polarized electron microscopy show that this graphene-induced Dzyaloshinskii-Moriya interaction can have similar magnitude as at interfaces with heavy metals. This work paves a new path towards two-dimensional material based spin orbitronics.
We study theoretically, via Monte Carlo simulations on lattices containing up to 1000 x 1000 spins, thermal creation of skyrmion lattices in a 2D ferromagnetic film with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction. At zero temperature, skyrmions only appear in the magnetization process in the presence of static disorder. Thermal fluctuations violate conservation of the topological charge and reduce the effective magnetic anisotropy that tends to suppress skyrmions. In accordance with recent experiments, we find that elevated temperatures assist the formation of skyrmion structures. Once such a structure is formed, it can be frozen into a regular skyrmion lattice by reducing the temperature. We investigate topological properties of skyrmion structures and find the average skyrmion size. Energies of domain and skyrmion states are computed. It is shown that skyrmion lattices have lower energy than labyrinth domains within a narrow field range.
The perpendicular magnetic anisotropy (PMA) at magnetic transition metal/oxide interfaces is a key element in building out-of-plane magnetized magnetic tunnel junctions for spin-transfer-torque magnetic random access memory (STT-MRAM). Size downscaling renders magnetic properties more sensitive to thermal effects. Thus, understanding temperature dependence of magnetic anisotropy becomes crucial. In this work, we theoretically address the correlation between temperature dependence of PMA and magnetization in typical Fe/MgO-based structures. In particular, the possible mechanisms behind experimentally reported deviations from the Callen and Callen scaling power law are analyzed. First-principles calculations reveal small high-order anisotropy terms ruling out an intrinsic microscopic mechanism underlying those deviations. Neglecting higher-order anisotropy terms in the atomisitic spin Hamiltonian, two possible extrinsic macroscopic mechanisms are unveiled: influence of the dead layer, always present in storage layer of STT-MRAM cells, and spatial inhomogeneities of interfacial magnetic anisotropy. We show that presence of a dead layer simultaneously with scaling the anisotropy constant by the total magnetization of the sample rather than that of the interface itself lead to low scaling powers. In the second mechanism, increasing the percentage of inhomogeneity in the interfacial PMA is revealed to decrease the scaling power. Apart from those different mechanisms, the layer-resolved temperature-dependence of PMA is shown to ideally follow the Callen and Callen scaling power law for each individual Fe layer. These results allow coherently explaining the difference in scaling powers relating anisotropy and magnetization thermal variations reported in earlier experiments. This is crucial for the understanding of the thermal stability of the storage layer magnetization in STT-MRAM applications.
Magnetic tunnel junctions with perpendicular anisotropy form the basis of the spin-transfer torque magnetic random-access memory (STT-MRAM), which is non-volatile, fast, dense, and has quasi-infinite write endurance and low power consumption. Based on density functional theory (DFT) calculations, we propose an alternative design of magnetic tunnel junctions comprising Fe(n)Co(m)Fe(n)/MgO storage layers with greatly enhanced perpendicular magnetic anisotropy (PMA) up to several mJ/m2, leveraging the interfacial perpendicular anisotropy of Fe/MgO along with a stress-induced bulk PMA discovered within bcc Co. This giant enhancement dominates the demagnetizing energy when increasing the film thickness. The tunneling magnetoresistance (TMR) estimated from the Julliere model is comparable with that of the pure Fe/MgO case. We discuss the advantages and pitfalls of a real-life fabrication of the structure and propose the Fe(3ML)Co(4ML)Fe(3ML) as a storage layer for MgO-based STT-MRAM cells. The large PMA in strained bcc Co is explained in the framework of Brunos model by the MgO-imposed strain and consequent changes in the energies of dyz and dz2 minority-spin bands.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
