Magnetic plasma confinement is a key element of fusion tokamak power plant design, yet changes in magnetic properties of alloys and steels occurring under neutron irradiation are often overlooked. We perform a quantitative study exploring how irradiation-induced precipitation affects magnetic properties of Fe-Cr alloys. Magnetic properties are simulated over a broad temperature interval using spin dynamics, implemented using a Hamiltonian including longitudinal and transverse magnetic degrees of freedom. Simulations of alloys with nominal Cr concentrations in the range 0-25~at.%, and different microstructures, including disordered solid solutions and large Cr-rich precipitates, show that the Curie temperature $T_C$ is always maximum when Cr solute concentration in the $alpha$ phase is close to 5-6~at.%. The magnetic properties of Fe-9~at.%Cr alloys are found to vary by 10%, depending on the size of Cr clusters. We compute the magnetic susceptibility and time-displaced correlation functions of $alpha’$ precipitates and (001) interfaces in Fe-Cr superlattices. A Cr interface disorders the Fe magnetic moments and acts as a nucleation site for the ferromagnetic-paramagnetic (FM-PM) transition with a lower effective $T_C$ and enhanced susceptibility. Cr moments in disordered Fe-Cr alloys are highly non-collinear at all temperatures. Magnetic moments at interfacial Cr atoms remain correlated far above the N'{e}el temperature, with correlations rapidly decreasing away from the interface. Spin dynamics simulations also offer insight into the time correlation functions and spin relaxation times in Fe-Cr alloys.