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Andres Saul (CINAM, Marseille)
February 14 @ 4:00 pm - 5:00 pm
Magneto elastic interactions in two antiferromagnetic systems under high magnetic field
Centre Interdisciplinaire de Nanoscience de Marseille
CNRS and Aix-Marseille Université, FRANCE
Many interesting physical properties account for the relation between measurable physical quantities of different kind. Piezomagnetism, for example, is the emergence of a magnetic moment under an applied mechanical stress and magnetostriction, the occurrence of a macroscopic deformation under an applied magnetic field. These two properties are the consequence of subtle interactions between the magnetic and structural degrees of freedom. In this seminar, I will discuss the physical origin of the magnetoelastic in two AFM systems.
The first system is the Shastry-Sutherland compound SrCu2(BO3)2 where the magnetically active Cu2+ ions form a 2D arrangement of mutually orthogonal dimers with frustrated intradimer and interdimer antiferromagnetic exchange interactions. The signature of the frustration is the presence of jumps and plateaus in the magnetization vs magnetic field curves. The interesting point in this system is that the macroscopic deformation vs magnetic field also show jumps and plateaus mimicking the magnetization.
Left: Atomic structure of SrCu2(BO3)2, (a) view along  and (b) view along . Dashed ellipses emphasize structural Cu dimers. Right: The low-temperature antiferromagnetic state of UO2 displaying the non-collinear AFM magnetic order (violet arrows) and oxygen displacements (green arrows, not to scale).
The second system is the prime nuclear fuel material UO2. At high temperature, this system has an fcc lattice and the magnetic moments of the U atoms are disordered. Below TN = 30.5 K, a non-collinear magnetic order with a 3-k structure accompanied by a static Jahn-Teller distortion of the oxygen cage is stablished. The macroscopic deformation versus applied magnetic field in the paramagnetic state (T ≥ TN) is proportional to the square of the magnetic field. Upon cooling into the antiferromagnetic state (T< TN) an additional positive linear term abruptly appears.
 G. Radtke, A. Saul, H. A. Dabkowska, M. B. Salomon, M. Jaime, “Magnetic nanopantograph in the SrCu2(BO3)2 Shastry-Sutherland lattice”; Proc. Natl. Acad. of Sci. USA 112, 1971, (2015).
 M. Jaime, A. Saul, M. B. Salamon, V. Zapf, N. Harrison, T. Durakiewicz, J. L
ashley, D. Andersson, C. Stanek, J. Smith, and K. Gofryk; “Piezomagnetism and magnetoelastic memory in uranium dioxide”; Nature. Communications 8, 99 (2017).