We study interactions of perpendicular and longitudinal magnetic fields in niobium films of different thickness in a wide range of temperatures below the superconducting transition temperature (T C ) . In 100 nm Nb film at all temperatures the longitudinal field H || practically does not influence the dynamics of the normal flux. However, in 200nm Nb film, a considerable anisotropy in the vortex motion is found with advanced propagation of the normal flux along H || at T>T C /2 and the preferential jump-wise growth of the thermomagnetic flux dendrites across H || at T

A superconducting flux injector (SFI) has been designed to allow for controlled injections of magnetic flux into a superconducting film from a predefined location along the edge. The SFI is activated by an external current pulse, here chosen to be 200 ms long, and it is demonstrated on films of Nb that the amount of injected flux is controlled by the pulse height. Examples of injections at two different temperatures where the flux enters by stimulated flux-flow and by triggered thermomagnetic avalanches are presented. The boundary between the two types of injection is determined and discussed. The SFI opens up for active use of phenomena which up to now have been considered hazardous for a safe operation of superconducting devices.

The electrodynamic behavior of isotropic superconducting Nb films cooled below their critical temperature in the presence of in-plane applied magnetic fields is investigated using magneto-optical imaging. A specially designed local flux injector is used to show that the frozen-in in-plane vortices strongly guide and enhance the penetration of perpendicular vortices, whereas their penetration across the array of in-plane vortices is essentially unchanged. This result provides the key to understanding why field-cooled square superconducting films show anisotropic nucleation of flux avalanches (jumps) along the four edges. The explanation is based on an analytical model for thermomagnetic avalanche nucleation in type-II superconducting films, and allows one to understand the entire scenario of different flux dynamics observed experimentally.

At ambient pressure and zero field, tetragonal CeAuSb 2 hosts stripe antiferromagnetic order at T N ¼ 6.3 K. Here, we first show via bulk thermodynamic probes and x-ray diffraction measurements that this magnetic order is connected with a structural phase transition to a superstructure that likely breaks C 4 symmetry, thus signaling nematic order. The temperature-field-pressure phase diagram of CeAuSb 2 subsequently reveals the emergence of additional ordered states under applied pressure at a multicritical point. Our phenomenological model supports the presence of a vestigial nematic phase in CeAuSb 2 akin to iron-based high-temperature superconductors; however, superconductivity, if present, remains to be discovered.

We report on magneto-optical imaging, magnetization, Hall effect and magnetoresistance experiments in Nb/Al 2 O 3 /Co thin film heterostructures.The magnetic field is applied perpendicularly to the plane of the film and gives rise to abrupt flux penetration of dendritic form. A magnetization texture is imprinted in the Co layer in perfect coincidence with these ramifications. The spin domains that mimic the vortex dendrites are stable upon the field removal. Moreover, the imprinted spin structure remains visible up to room temperature. Complementary magnetization, Hall effect and magneto-resistance experiments were performed in a similar sample where electrical contacts were placed on the Co layer. In the region of the field -temperature diagram where flux instabilities are known to occur in Nb films, irregular jumps are observed in the magnetic hysteresis and large amplitude noise is detected in the magneto-resistance and Hall resistivity data when measured as a function of the field.