Measurements on the Anomalous Temperature Dependence of the C44 Shear Modulus for Single-Crystal MnO
Mentor:Donald Isaak, Associate Dean , Azusa Pacific University
Elastic moduli describe how materials strain in response to applied stresses; thus, they are fundamental properties of interest to a range of scientific disciplines, including theoretical solid state physics, materials and engineering science, and geophysics. In general, elastic moduli increase with rising pressure and decrease with rising temperature. Some exceptions to these trends are found, however, when the material is near a phase transition in pressure and temperature space. For example, the transition metal monoxides FeO and MnO undergo an antiferromagnetic phase change at low temperature which results in the temperature derivative of their C44 shear moduli being positive near room temperature. Most previous work on documenting this anomalous temperature dependence of the C44 modulus has been at low temperatures near the region where the antiferromagnetic phase transition occurs. However, it is worth seeing how the anomalous temperature derivative of the C44 modulus changes at elevated temperature. We use resonant ultrasound spectroscopy (RUS) to measure the temperature dependences of the full elastic modulus tensor of MnO to more than 200 kelvins beyond ambient temperature. We compare our results with those from another study on MnO and with our previous results on FeO.