Using the magnetic force microscopy, the magnetic properties (switching field) and transition from multi-domain to single-domain magnetic state of planar Co18Ni82 microparticles with the size 7.5×7.5×0.03 mkm3 was studied at various temperatures. The relatively low heating or cooling the sample compared to the deposition temperature made it possible to induce uniaxial mechanical stresses in microparticles, since the using hexagonal single crystal of lithium niobate as a substrate. This crystal has different linear expansion coefficients along different crystallographic axes. It was shown that, the switching field decreases sevenfold when temperature increasing by only 50 K due to the thermally induced magnetoelastic effect.