Abstract
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.
Highlights
Actinide materials exhibit strong spin–lattice coupling and electronic correlations, and are predicted to host new emerging ground states
Piezomagnetism is utilized in geology where the so-called volcanomagnetic effect is used for monitoring volcanic activities[17,18,19]
When the UO2 crystal is cooled below the magnetic transition temperature, the application of a magnetic field causes positive magnetostriction in agreement with the measurements of the macroscopic variation of the sample length using a fiber Bragg grating (FBG) technique[13]
Summary
Actinide materials exhibit strong spin–lattice coupling and electronic correlations, and are predicted to host new emerging ground states. An unexpected splitting of the [888] peak is observed, indicating the simultaneous presence of timereversed 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. It has been shown that, due to the magnetic symmetry of the non-collinear 3k antiferromagnetic order (shown in the inset of Fig. 1a) and strong magneto-elastic coupling, UO2 undergoes a trigonal distortion under magnetic field and becomes a piezomagnet with exceptionally large coercive characteristics[13]. X-rays offer additional insight not available via bulk FBG methods—we observe a splitting of the [888] peak under the magnetic field This arises from time-reversed (TR) domains of 3-k magnetic structures that have different responses to the applied magnetic fields. To the best of our knowledge, this study represents the first crystallographic observation of piezomagnetism and the switching effect in general, and in a 5f-electron spin system in particular
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