Application of strain to orbital-spin-coupled system MnV₂O₄at cryogenic temperatures within a transmission electron microscope

Abstract

The impact of mechanical stress on the morphology of crystallographic and magnetic domains in shape-controlled specimens of an orbital-spin-coupled system, MnV2O4, was examined by cryogenic Lorentz microscopy. Because of the difference in thermal expansion coefficients of MnV2O4 and the supporting Mo mesh, compression on the order of 0.01% was applied to the thin-foil specimens near the structural/magnetic phase transformation temperatures. The extent of compression was comparable to the lattice striction associated with the cubic-to-tetragonal phase transformation in MnV2O4 The applied strain thus clearly influenced the morphology of crystallographic domains (i.e. twinning configuration in the tetragonal phase) produced during cooling. The magnetic domain structure was entirely dependent on the configuration of twinning in the tetragonal phase. The observations in this study provided useful information for understanding the relationship between the crystallographic domains and the magnetic domains in MnV2O4.

Real-space magnetic imaging of the multiferroic spinels MnV2O4 and Mn3O4Wolin1, Wang2, Naibert3 et al. 2018Phys. Rev. Materials59250View full textAdd to dashboardCite

“…In Mn3O4, an observed correlation between stripe width and encompassing tetragonal domain size evidences a connection between mechanical strain and the magnetic patterns. In MnV2O4, we observe 100 nm-scale stripe modulations consistent with recent zeromagnetic-field TEM measurements of thin-foil MnV 2O4 [42], and we find different magnetic behaviors in the high-and low-strain MnV2O4 samples. We also present a quantitative estimate of the local magnetization associated with these stripe domains in MnV2O4.…”

“…cell-doubled orthorhombic phases at low temperatures [52], consistent with the presence of a mesoscale structural modulation in this material. In MnV 2O4, TEM measurements revealed the coexistence of tetragonal twinning domains with different c-axis orientations [42], and the sensitivity to strain we observe in our measurements of MnV 2O4 support the conclusion that the nanoscale magnetic modulation we observe in this material is associated with an underlying structural modulation. Altogether, these results provide strong evidence that the magnetic modulations observed with MFM in both MnV 2O4 and Mn3O4 are associated with an underlying structural modulation that betrays the strong coupling of spin, orbital, and structural degrees of freedom in these materials [36,37].…”

“…A similar order-ofmagnitude difference in thermal expansion coefficients between MnV 2O4 foil and the Mo mount resulted in an estimated 0.03% compressive strain in MnV 2O4 at 87 K and a <0.1% compressive strain near the cubic-to-tetragonal transition at 52K in MnV 2O4 [42]. While this estimated compressive strain is less than the ~0.15% lattice striction measured in MnV2O4 at the cubic-to-tetragonal transition [37], it is large enough to influence domain formation in MnV 2O4 [42]. The second MnV2O4 sample was a full-boule cylinder having a 5mm diameter and a 2mm length, and was specifically prepared to minimize mechanical strain below T=77K.…”

“…Epoxy was applied to the entire back surface of this sample, which was then attached to a sapphire backing-plate. The total thermal contraction occurring between the epoxy curing temperature and the base temperature used in this study (T=4K) is ten times larger for the epoxy than for the MnV 2O4, and therefore significant mechanical strain is induced in the sample below T=77K [42]. A similar order-ofmagnitude difference in thermal expansion coefficients between MnV 2O4 foil and the Mo mount resulted in an estimated 0.03% compressive strain in MnV 2O4 at 87 K and a <0.1% compressive strain near the cubic-to-tetragonal transition at 52K in MnV 2O4 [42].…”

“…The total thermal contraction occurring between the epoxy curing temperature and the base temperature used in this study (T=4K) is ten times larger for the epoxy than for the MnV 2O4, and therefore significant mechanical strain is induced in the sample below T=77K [42]. A similar order-ofmagnitude difference in thermal expansion coefficients between MnV 2O4 foil and the Mo mount resulted in an estimated 0.03% compressive strain in MnV 2O4 at 87 K and a <0.1% compressive strain near the cubic-to-tetragonal transition at 52K in MnV 2O4 [42]. While this estimated compressive strain is less than the ~0.15% lattice striction measured in MnV2O4 at the cubic-to-tetragonal transition [37], it is large enough to influence domain formation in MnV 2O4 [42].…”