Abstract: The magnetic-force microscopy has been used to study the magnetic properties (switching field) and the transitions from a multidomain state to a single-domain state of planar Co18Ni82 microparticles with sizes 7.5 × 7.5 × 0.03 μm3 at various temperatures. The use of a hexagonal single-crystal lithium niobate, which has different temperature linear expansion coefficients along different crystallographic axes as a substrate makes it possible to induce uniaxial mechanical stresses in microparticles by relatively insignificant heating or cooling a sample as compared to its deposition temperature. It is shown that the increase in temperature only by 50 K due to the thermostimulated magnetoelastic effect can lead to the seven-fold decrease in the switching field.