is spontaneous magnetization and magnetic susceptibility a thermodynamic properties? Are spontaneous magnetization and magnetic susceptibility a thermodynamic property? How do you determine whether a property is thermodynamic or not?
 A: A macroscopic magnetic system is a thermodynamic system like that of a hydrostatic system. The former is described by the thermodynamic variables $(\textbf{H},\textbf{M},T)$ and the latter by $(P,V,T)$. Therefore, magnetization $\textbf{M}$ (not necessarily spontaneous) is a thermodynamic property and it's the analog of volume $V$ for a hydrostatic system or a fluid. The magnetic field $\textbf{H}$ is the analog of fluid pressure $P$. The susceptibility is a response function for magnetic systems and is the analog of the compressibility of a fluid system.
If by thermodynamic property you mean gross property of the system then yes. Both the magnetization and susceptibility are properties belonging to the system as a whole. 
But if by thermodynamic property you mean thermodynamic coordinates or state variables then those are the set of macroscopic quantities required to completely describe the state of the system at a particular instant of time in equilibrium. They are $(\textbf{H},\textbf{M}, T)$ for a magnetic system.  
