Note: This planet is orbiting a Sun-like star at a distance of 1 AUI think it wouldn‘t have a magnetic field because a requirement for a magnetic field is that there is an interior region of electrically conducting fluid (liquid or gas), such as molten material.
That is correct. Most scientific theories suggest this is actually what happened with mars. When the core freezes and becomes a solid, the magnetic field stops. When this happens, the solar winds strip the planet of it's atmosphere.
