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Gallery of magneto-optical images

Electromagnetic response of unconventional superconductors
Precise measurements of the magnetic penetration depth are performed at low temperatures and magnetic fields up to 9 Tesla by using a tunnel-diode diode resonator. pico-EMU resolution allows us to study among other effects:
- structure of the superconducting gap
- anisotropy of the superfluid density tensor
- coexistence of superconductivity and magnetism
- surface bound states
- proximity effect
- reversible and irreversible properties in the mixed state

Magnetic domains formation and relation to physical properties
Magneto-optical Faraday and Kerr effects are used to map magnetic domains on surfaces of ferromagnetic materials at variable temperature. Quantitative analysis allows studying various questions including local spin structure change during magnetic transitions (e.g. spin reorientation in Nd₂Fe₁₄B at 130 K) and precise topology of the ferromagnetic ground state.

Dynamics of magnetic transitions
Several AC techniques covering wide magnetic field, temperature and frequency range are used to study dynamics of the magnetic transitions. Areas of particular interests are:
- metamagnetism
- magnetic molecules
- magnetic glasses, ferrofluids
- critical scaling near T_c
- differences between local and itinerant ferromagnets
- ferromagnetic insulators and metals

Structure of the intermediate state in type-I superconductors
Direct visualization of the magnetic fields (based on magneto-optical Faraday effect) is used to study real-time formation and evolution of the intermediate state patterns in stress- and defect- free type-I superconductors. AC and DC magnetic susceptibility and conductivity measurements are performed to analyze the correlation between topology and magnetic properties as well as the relation of the observed behavior to other chemical, biological and mathematical systems.
Funded by the National Science Foundation under grant No. DMR-0553285

Catastrophic behavior in type-II superconductors
Some superconductors exhibit avalanche - like dynamics usually associated with thermo-magnetic instabilities of the vortex lattice. We study this behavior using magneto-optical, DC and AC magnetization, transport and thermal techniques.

Superparamagnetic and superconducting nanocomposites
Sonochemical synthesis is used to produce ceramic-based nanocomposites with ferromagnetic nanoparticles as active elements.
- In the case of superconductors, nanoparticles play role of efficient pinning centers. The main focus of the project is to understand the behavior of magnetic nanoparticles embedded into the bulk of a superconductor and their interaction with vortices.
- In case of refractory ceramics, the use of nanoparticles result in superparamagnetic behavior. We study frequency response of such systems in a wide range of chemical, structural and physical parameters.
Funded by the National Science Foundation under grant No. DMR-0603841

Quantum criticality
The same technique is used to measure temperature-dependent dynamic magnetic response in materials exhibiting apparent transition in their ground state. In particular,
- metallic systems exhibiting a crossover from conventional to non Fermi - liquid behavior.
- in electron-doped high-T_c superconductors we search for signatures of quantum criticality reflected in a variation of the superfluid density with the change of doping and external parameters.