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The discrete vortex lattices in a ferromagnet/superconductor bilayer are studied when the ferromagnet has periodic stripe domains with an out-of-plane magnetization. The vortices are assumed to be situated periodically on chains in the stripe domains. Only up to two vortex chains per domain configurations are considered. When the domain period is fixed, the threshold magnetization is calculated at which the transition from the Meissner state to the mixed state occurs. When the domain period is not fixed, the equilibrium domain size and vortex positions are calculated, depending on the domain's magnetization and the domain wall energy. In equilibrium, the vortices in the neighbor domains are half-way shifted, while they are next to each other in the same domain., Comment: 11 Pages, 11 Figures

The photoinduced magnetism in manganese-tetracyanoethylene (Mn-TCNE) molecule-based magnets is ascribed to charge-transfer excitations from manganese to TCNE. Charge-transfer energies are calculated using Density Functional Theory; photoinduced magnetization is described using a model Hamiltonian based on a double-exchange mechanism. Photoexciting electrons from the manganese core spin into the lowest unoccupied orbital of TCNE with photon energies around 3 eV increases the magnetization through a reduction of the canting angle of the manganese core spins for an average electron density on TCNE less than one. When photoexciting with a smaller energy, divalent TCNE molecules are formed. The delocalization of the excited electron causes a local spin flip of a manganese core spin., Comment: 4 pages, 4 figures

The continuum theory of domain structures in ferromagnetic/superconducting bilayers fails when the equilibrium domain size becomes comparable with effective penetration depth $\Lambda$. Instead, a lattice of discrete vortices must be considered. Here, we report our results on the discrete vortex lattices in stripe domain structures of ferromagnetic/superconducting bilayers. The vortices are assumed to be situated periodically on chains in stripe domains. We study the configurations containing up to three chains per domain, and calculate their equilibrium energies, equilibrium domain size and vortex positions through a method based on London-Maxwell equations. In equilibrium, the vortices in the neighbor domains are half-way shifted while they are next to each other in the same domain. Additionally, more vortex chains per domain appear spontaneously depending on magnetization and domain wall energy., Comment: submitted to Phys.Rev.B

Here we report a study of vortex states in a thin superconducting film with a magnetic dot grown upon it by means of a method based on London-Maxwell equations. Vortices with single quantum flux ($\Phi_0 = h c / 2 e$), giant vortices (vortices with multiple flux) as well as antivortices (vortices with negative vorticity) are taken into consideration. It turns out that giant vortices occur, when the dot's size is sufficiently smaller ($R \leq 4.5 \xi $) than the effective penetration depth $\Lambda$. In the case of a dot with sufficiently large size ($R \geq 6 \xi $), the vortices with single quantum flux dominate the vortex states. Their geometrical patterns are predicted up to seven vortices. Our calculations do not show the spontaneous appearance of antivortices., Comment: 17 figures

Heterogeneous magnetic superconducting systems (HMSS) represent a new class of nanostructures. They are made of ferromagnetic (FM) and superconducting (SC) pieces separated by thin layers of insulating oxides. In contrast to the case of a homogeneous ferromagnetic superconductor studied during the last two decades, the two order parameters, the magnetization and the SC electron density do not suppress each other. In HMSS, the interaction between the two order parameters is due to the magnetic field created by the magnetic and SC textures. Strong interaction of the FM and SC systems not only gives rise to a new class of novel phenomena and physical effects, but also shows the important technological promise of devices whose transport properties can be easily tuned by comparatively weak magnetic fields.

We report our results on vortex penetration in two realizations of heterogeneos magneto-superconducting systems (HMSS) based on London approach; semi-infinite ferromagnetic(FM)-superconducting(SC) bilayers and a FM dot on a semi-infinite SC film. In the first case, we study quantitatively the vortex entry in FM-SC bilayers which manifests Bean-Livingston-like vortex barrier, controlled by FM film's magnetization $m$ and SC film's Ginzburg parameter $\kappa$. In the second case, we investigate the conditions for sponteneous vortex creation and determine the position of vortex for various values of magnetization and the dot's position., Comment: accepted for publication in Phys Rev B

We study the equilibrium state of a superconducting film covered with a regular square array of perpendicularly magnetized magnetic dots. The dots induce vortices in the film directly under them and antivortices between the dots. We show that the symmetry of the dot array is spontaneously violated by the vortices. The positions of the vortices and the antivortices depend on the magnetization and the size of the dots., Comment: 6 pages, 3 figures