Magnetic phase transitions studied by magnetic force microscopy

Magnetic force microscopy (MFM) fills the important gap between largely opt ical real space magnetic microscopies and reciprocal space probe neutron sc attering (sensitive mainly to phenomena on length scales below 20 nm). To i llustrate this, we describe magnetic phase transitions in Pd1-xCox and La1- xSrxMnO3 films studied using MFM with a variable temperature (T) sample sta ge. The evolution of magnetic domain patterns as a function of T was invest igated in detail for both films. Although the magnetic contrast decreases a s T is raised towards the Curie point T-c, the domain sizes are T-independe nt. From the T dependence of the magnetic contrast we obtained the T depend ence of the magnetic order parameter M(T) at zero external field. Using thi s local probe, we discovered that La1-xSrxMnO3 films are magnetically inhom ogeneous, with regions around grain boundaries or defects having a T-c 20 K higher than the bulk of the film. (C) 2001 Elsevier Science B.V. All right s reserved.