FOMP
![Magnetic phase diagram of the uniaxial ferromagnet:
left) for K1>0 ; right) for K1<0 . See text for symbol explanations.](/Images/godic/202501/13/Fomp_magnetic_phaseN0437.png")
![. See text for label explanations.](/Images/godic/202501/13/Fomp_examplesN0437.png")
![FOMP phase diagram of the uniaxial ferromagnet: left) for K1>0 ; right) for K1<0 . See text for label explanations.](/Images/godic/202501/13/Fomp_phaseN0438.png")
![Computer simulation of the magnetization of polycrystal sample with K1>0, K2 / K1=0.5, K3 / K1=-0.5 (<m>, red curve). The green is the first derivative <m'>=∂<m>/∂h. While the black ones are the magnetization (m) of the corresponding single crystal with H applied along c-axis (γ=90), γ=85 and γ=81.](/Images/godic/202501/13/Fomp_polycrystalN0438.png")
The magnetocrystalline anisotropy energy of a ferromagnetic crystal can be expressed as a power series of direction cosines of the magnetic moment with respect to the crystal axes. The coefficient of those terms are the anisotropy constant. In general the expansion is limited to few terms. Normally the magnetization curve is continuous respect to applied field up to saturation but, in certain intervals of the anisotropy constant values, irreversible field induced rotations of the magnetization are possible implying first order magnetization transition between equivalent magnetization minima, the so-called first order magnetization process (FOMP).