Solar magnetic fields span a wide range of spatial scales from sunspots and plages to magnetic bright points. A clear understanding of the physical processes underlying the evolution of these magnetic features requires high-resolution spectropolarimetric observations of solar active regions and comparisons with synthetic data from simulations. This thesis is based on observations with the Swedish 1-m Solar Telescope (SST) and the CRISP imaging spectropolarimeter which, processed with a sophisticated image restoration technique, produce data of unsurpassed quality. The Fe I 630.25 nm line is used for all the spectropolarimetric observations. It appears likely that present telescopes resolve the fundamental scales of penumbral filaments. However, the penumbrae of sunspots are still not fully understood, with various theoretical models competing to explain their fine structure and flows. We analyze spectropolarimetric observations with a resolution close to the SST diffraction limit of 0.16 arcsecond. Using inversion techniques, we map the line-of-sight velocities and the magnetic-field configuration of dark-cored penumbral filaments. Over the past decade, sunspots and quiet sun magnetic fields have received considerable attention, with intermediate plage regions being somewhat neglected. We perform a detailed analysis of a plage region and present the first observational evidence of a small-scale granular magneto-convection pattern associated with a plage region. Magnetic bright points are believed to be formed due to magnetic field intensification caused by flux-tube collapse involving strong downflows. Although magneto-hydrodynamic (MHD) simulations agree with this view, only a few observations with adequate spatial resolution exist in support of the simulations. We present several cases of bright-point formation associated with strong downflows, which qualitatively agree with simulations and past observations. However, we find the field intensification to be transient rather than permanent. / At the time of the doctoral defense, the following paper was unpublished: Paper 3: Accepted.

With  the  continuous  advances  in  microwave  technology,  microwave  components  and  related magnetic materials become more important in industrial environment. In order to further develop the microwave components, it is of interest to find new kinds of technologies and materials. Here, we  introduce  a  new  kind  of  material  --  amorphous  metallic  wires  which  could  be  used  in microwave  components,  and  use  these  wires  to  design  new  kinds  of  attenuators.  Based  on  the fundamental  magnetic  properties  of  amorphous  wires  and  transmission  line  theory,  we  design  a series of experiments focusing on these wires, and analyze all the experimental results.    Experimental  results  show  that  incident  and  reflected  signals  produce  interference  and  generate standing  waves  along  the  wire.  At  given  frequency,  the  insertion  attenuation  S21 [dB]  of  an amorphous wire increases monotonically with dc bias current. The glass cover will influence the  magnetic  domain  structure  in  amorphous  metallic  wires.  Therefore,  it  will  affect  the circumference  permeability  and  change  the  signal  attenuation.  It  is  necessary  to  achieve  the impedance  matching  by  coupling  to  an  inductor  and  a  capacitor  in  the  circuit.  The  impedance matching  makes  the  load  impedance  close  to  the  characteristic  impedance  of  transmission  line. The magnetic wire-based attenuator designed in this thesis work are characterized and compared to conventional pin-diode attenuator.