Piezomagnetism and magnetoelastic memory in uranium dioxide

Abstract

The thermal and magnetic properties of uranium dioxide, a prime nuclear fuel and thoroughly studied actinide material, remain a long standing puzzle, a result of strong coupling between magnetism and lattice vibrations. The magnetic state of this cubic material is characterized by a 3-k non-collinear antiferromagnetic structure and multidomain Jahn-Teller distortions, likely related to its anisotropic thermal properties. Here we show that single crystals of uranium dioxide subjected to strong magnetic fields along threefold axes in the magnetic state exhibit the abrupt appearance of positive linear magnetostriction, leading to a trigonal distortion. Upon reversal of the field the linear term also reverses sign, a hallmark of piezomagnetism. A switching phenomenon occurs at ±18 T, which persists during subsequent field reversals, demonstrating a robust magneto-elastic memory that makes uranium dioxide the hardest piezomagnet known. A model including a strong magnetic anisotropy, elastic, Zeeman, Heisenberg exchange, and magnetoelastic contributions to the total energy is proposed.

Magnetoelastic couplings in the deformed kagome quantum spin lattice of volborthite

“…. being constants, is usually expected for a variety of magnetic systems based on the symmetry considerations on the magnetic point groups [18,19].…”

Fiber Bragg Grating Dilatometry in Extreme Magnetic Field and Cryogenic Conditions

“…The magnetostriction ΔL/L changes sign again when the magnetic field direction is reversed to positive (4) and becomes reversible when a second pulse is applied in the same direction (5). These results first discovered piezomagnetism in UO 2 , a technologically important material and also the strongest piezomagnet known [23]. These data were obtained using the 46 kHz line array InGaAs camera described in Section 2.2 below.…”

“…Sensing of magnetostriction with single mode SiO 2 FBGs in pulsed magnetic fields is successfully utilized at the National High Magnetic Field Laboratory (NHMFL) with a resolution as good as a few parts per hundred million ( ΔL/L ≈ 10 −8 ) in the best cases. This capability allows for the study of a variety of insulating and metallic condensed matter systems including geometrically frustrated magnets, quantum magnets, multiferroics, and uranium- and cerium-based antiferromagnets [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]. Figure 1 shows an example of magnetoelastic effects in pulsed magnetic fields to 60 T at cryogenic temperatures on a sample of uranium dioxide (UO 2 ), which is the most commonly used nuclear fuel.…”

“…The intriguing behavior exhibited by this material, i.e., a field-induced strain butterfly loop characteristic of piezomagnets, is due to its peculiar 3 k -type antiferromagnetic state below T = 30 K that breaks time-reversal symmetry. The record high switching fields at ±18 T mark antiferromagnetic domains that flip [23]. In this review paper, we discuss experimental approaches that are used in three different timescales (milliseconds, microseconds, and nanoseconds), as well as the technique applicability, sensitivity, and advantages over traditional methods.…”

Magnetoelastics of High Field Phenomena in Antiferromagnets UO2 and CeRhIn5

“…The coincidence of this local minimum in κ(T) with the AFM ordering temperature is suggestive of a phonon mean free path that is dramatically reduced by some kind of magnetically correlated crystal bond disorder and/or soft-phonon phenomenon. The first order nature of the phase transition at T N makes this puzzle especially intriguing, and it has been proposed that magnetic fields could be a relevant tuning parameter [7], [8].…”