Testing of thermal expansion and magnetostrictive effect of magnetic phase transition materials

A characterization method for the thermal expansion coefficient of magnetic phase transition materials was developed using strain gauge testing methods based on a comprehensive physical performance testing system in low－temperature and magnetic field environments. The reliability of the test results was verified, and the negative expansion performance of magnetic phase transition materials LaFe₁₁Co_0.8Si_1.2 was studied. The results show that at the Curie temperature, the thermal expansion of LaFe₁₁Co_0.8Si_1.2 material decreased with the increased of temperature. The reason was that the material undergone a magnetic phase transition from ferromagnetism to paramagnetism, resulting in magnetostriction effect and offsetting the thermal expansion and contraction caused by atomic non harmonic vibration, ultimately led to negative thermal expansion of the material.