# Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Ferromagnetic resonance

FMR arises from the precessional motion of the (usually quite large) magnetization $\vec{B}$ of a ferromagnetic material in an external magnetic field H0. The magnetic field exerts a torque on the sample magnetization which causes the magnetic moments in the sample to precess. The precession frequency of the magnetization depends on the orientation of the material, the strength of the magnetic field, as well as the macroscopic magnetization of the sample; the effective precession frequency of the ferromagnet is much lower in value from the precession frequency observed for free electrons in ESR or EPR. Moreover, linewidths of absorption peaks can be greatly affected both by dipolar-narrowing and exchange-broadening (quantum) effects. Furthermore, not all absorption peaks observed in FMR are caused by the precession of the magnetic moments of electrons in the ferromagnet. Thus, the theoretical analysis of FMR spectra is far more complex than that of ESR or NMR spectra.