Piezomagnetic switching and complex phase equilibria in uranium dioxide

Actinide materials exhibit strong spin-lattice coupling and electronic correlations, and are predicted to host new emerging ground states. One example is piezomagnetism and magneto-elastic memory effect in the antiferromagnetic Mott-Hubbard insulator uranium dioxide, though its microscopic nature is under debate. Here, we report X-ray diffraction studies of oriented uranium dioxide crystals under strong pulsed magnetic fields. In the antiferromagnetic state a [888] Bragg diffraction peak follows the bulk magnetostriction that expands under magnetic fields. Upon reversal of the field the expansion turns to contraction, before the [888] peak follows the switching effect and piezomagnetic 'butterfly' behaviour, characteristic of two structures connected by time reversal symmetry. An unexpected splitting of the [888] peak is observed, indicating the simultaneous presence of time-reversed domains of the 3-k structure and a complex magnetic-field-induced evolution of the microstructure. These findings open the door for a microscopic understanding of the piezomagnetism and magnetic coupling across strong magneto-elastic interactions. UO2 is an antiferromagnetic Mott-Hubbard insulator and exhibits piezomagnetism, though the origin of this is elusive. Here, X-ray diffraction of UO2 in pulsed magnetic fields reveals the presence of time-reversed magnetic domains and structural distortions that take place during the piezomagnetic switching.

Automated summary

Research on uranium dioxide crystals in the antiferromagnetic state under strong magnetic fields reveals the presence of piezomagnetism and magneto-elastic memory effect. The unexpected splitting of the [888] Bragg diffraction peak indicates the simultaneous existence of time-reversed magnetic domains and structural distortions. This study provides insights into the microscopic understanding of piezomagnetism and magnetic coupling in actinide materials.