Planetary-scale magnetic fields provide a unique window into a planet's deep interior. From the magnetic field of Earth to that of Jupiter, the existence of such fields is tied to the presence of an electrically conductive convecting fluid (dynamo source region) in the interior. Thus, detections of planetary-scale magnetic field signals offer constraints on the planets’ thermal state, interior structure, and dynamics. In this thesis, we present thermal evolution calculations for rocky exoplanets. We aim to determine whether super-Earths can host dynamo-generated magnetic fields and explore how dynamo lifetimes scale with planet properties (such as planet mass, M_pl, and core mass fraction, CMF). To achieve this, we couple a 1D thermal evolution model with a Henyey solver to calculate their thermal evolution. The code solves the energy balance equation in the iron-dominated core and the silicate mantle. We use a modified mixing length formulation to model convection in the silicate mantle with low and high Reynolds numbers. In addition, by including the Henyey solver, the model self-consistently accounts for adjustments in the interior structure as the planet evolves in time. We explore the possibility of the planet hosting a dynamo source in its iron-dominated core and/or magma ocean. We find that the heat loss rate of the core scales with M_pl. This results in a greater dynamo lifetime in the core of a more massive planet with M_pl<6M_Earth. However, for planets with M_pl>6M_Earth, the core fully solidifies before liquid core convection shuts off. The dynamo lifetime in the core decreases with increasing M_pl, owing to the short lifetime of the liquid core associated with the high core heat loss rate. In addition, a magma ocean could only host a dynamo if its melt fraction is high enough to have liquid-like convection. The dynamo in the magma ocean in an Earth-like planet (M_pl=1M_Earth, CMF=0.33 and T_eq=255K) could only last ~0.25Myr. However, a magma ocean may sustain a long-term dynamo on a lava planet or a sub-Neptune, whose silicate mantle could stay molten or partially molten on a billion-year timescale. Future studies of these planets may shed light on the role of a magma ocean sustaining a planetary-scale magnetic field.