Magnetic phase transitions studied by magnetic force microscopy

Abstract Magnetic force microscopy (MFM) fills the important gap between largely optical real space magnetic microscopies and reciprocal space probe neutron scattering (sensitive mainly to phenomena on length scales below 20 nm). To illustrate this, we describe magnetic phase transitions in Pd 1− x Co x and La 1− x Sr x MnO 3 films studied using MFM with a variable temperature ( T ) sample stage. The evolution of magnetic domain patterns as a function of T was investigated in detail for both films. Although the magnetic contrast decreases as T is raised towards the Curie point T c , the domain sizes are T -independent. From the T dependence of the magnetic contrast we obtained the T dependence of the magnetic order parameter M ( T ) at zero external field. Using this local probe, we discovered that La 1− x Sr x MnO 3 films are magnetically inhomogeneous, with regions around grain boundaries or defects having a T c 20 K higher than the bulk of the film.