Study of Anisotropy on Ferromagnetic Electrodes of a Magnetic Tunnel Junction (MTJ)-Based Molecular Spintronics Device (MTJMSD)

Magnetic tunnel junction-based molecular spintronics devices (MTJMSDs) are designed by covalently connecting the paramagnetic molecules across two ferromagnets (FM) electrodes of a magnetic tunnel junction (MTJ). MTJMSD provides opportunities to connect FM electrodes of a vast range of anisotropy properties to a variety of molecules of length scale. Our prior studies showed that the paramagnetic molecules can produce strong antiferromagnetic coupling with FM electrodes. The device properties of MTJMSD depend upon various factors such as anisotropy, spin fluctuation, thermal energy, etc. In this paper, we report a theoretical Monte Carlo Simulation (MCS) study to explain the impact of anisotropy on the MTJMSD equilibrium properties. We studied the energy variation of the MTJMSD system with time as a function of FM electrode anisotropy. Experimentally designed FM electrodes of MTJMSD contain multi-layers of different ferromagnetic materials. These materials possess in-plane and out-of-plane magnetic anisotropy characteristics. To understand the competing effect of in-plane and out-of-plane anisotropy, we have computationally applied anisotropies on the left FM electrode. For the MCS study, the orientation of the device was kept along YZ plane. As a result, the applied anisotropy along the X-direction (\mathbit{A}_{\mathbit{Lx}}) and Y-direction (\mathbit{A}_{\mathbit{Ly}}) represent out-of-plane and in-plane anisotropy, respectively. We found that increasing anisotropy strength starts exhibiting diverse domain structures within an FM electrode. Increasing the magnitude of anisotropy was found to create stripe-shaped domains with opposite spins. These domains represent the different magnetic phases. However, the application of equal magnitude of in-plane and out-of-plane cancels the strip domain formation and lowers the magnetic moment of overall MTJMSD.
Comment: 5 Pages, four figures