Robust Ferromagnetic State Research Articles

Giant Nonvolatile Electric Field Control of Proximity‐Induced Magnetism in the Spin–Orbit Semimetal SrIrO3

AbstractWith its potential for drastically reduced operation power of information processing devices, electric field control of magnetism has generated huge research interest. Recently, novel perspectives offered by the inherently large spin–orbit coupling of 5d transition metals have emerged. Here, nonvolatile electrical control of the proximity‐induced magnetism in SrIrO3 based back‐gated heterostructures is demonstrated. Up to a 700% variation of the anomalous Hall conductivity (σAHE) and Hall angle (ΘAHE) as function of the applied gate voltage Vg is reported. In contrast, the Curie temperature TC ≈ 100 K and magnetic anisotropy of the system remain essentially unaffected by Vg indicating a robust ferromagnetic state in SrIrO3 which strongly hints to gating‐induced changes of the anomalous Berry curvature. The electric‐field induced ferroelectric‐like state of SrTiO3 enables nonvolatile switching behavior of σAHE and ΘAHE below 60 K. The large tunability of this system, opens new avenues toward efficient electric‐field manipulation of magnetism.

Strain-tunable magnetic anisotropy in two-dimensional Dirac half-metals: nickel trihalides.

The recent discovery of intrinsic two-dimensional (2D) ferromagnetism has sparked intense interest due to the potential applications in spintronics. Magnetic anisotropy energy defines the stability of magnetization in a specific direction with respect to the crystal lattice and is an important parameter for nanoscale applications. In this work, using first-principles calculations we predict that 2D NiX3 (X = Cl, Br, and I) can be a family of intrinsic Dirac half-metals characterized by a band structure with an insulator gap in one spin channel and a Dirac cone in the other. The combination of 100% spin polarization and massless Dirac fermions renders the monolayer NiX3 a superior candidate material for efficient spin injection and high spin mobility. The NiX3 is dynamically and thermodynamically stable up to high temperature and the magnetic moment of about 1 μB per Ni3+ ion is observed with high Curie temperature and large magnetic anisotropy energy. Moreover, detailed calculations of their energetics, atomic structures, and electronic structures under the influence of a biaxial strain ε have been carried out. The magnetic anisotropy energy also exhibits a strain dependence in monolayer NiX3. The hybridization between Ni dxy and dx2-y2 orbitals gives the largest magnetic anisotropy contribution, whether for the off-plane magnetized NiCl3 (NiBr3) or the in-plane magnetized NiI3. The outstanding attributes of monolayer NiX3 will substantially broaden the applicability of 2D magnetism for a wide range of applications.

Magnetic and superconducting phases at the LaAlO3/SrTiO3interface: The role of interfacial Ti 3delectrons

Ferromagnetism and superconductivity are in most cases adverse. However, recent experiments reveal that they coexist at interfaces of LaAlO3 and SrTiO3. We analyze the magnetic state within density functional theory and provide evidence that magnetism is not an intrinsic property of the two-dimensional electron liquid at the interface. We demonstrate that the robust ferromagnetic state is induced by the oxygen vacancies in SrTiO3- or in the LaAlO3-layer. This allows for the notion that areas with increased density of oxygen vacancies produce ferromagnetic puddles and account for the previous observation of a superparamagnetic behavior in the superconducting state.

Magnetic States at the Oxygen Surfaces of ZnO and Co-Doped ZnO

First principles calculations of the O surfaces of Co-ZnO show that substitutional Co ions develop large magnetic moments which long-range order depends on their mutual distance. The local spin polarization induced at the O atoms is 3 times larger at the surface than in the bulk, and the surface stability is considerably reinforced by Co. Moreover, a robust ferromagnetic state is predicted at the O (0001) surface even in the absence of magnetic atoms, correlated with the number of p holes in the valence band of the oxide, and with a highly anisotropic distribution of the magnetic charge even in the absence of spin-orbit coupling.