Giant magnetoelastic spin-flop with magnetocrystalline instability in La1.4Sr1.6Mn2O7

We studied a low-field giant magnetostrictive spin-flop transition in a colossal magnetoresistance manganite ${\mathrm{La}}_{1.4}{\mathrm{Sr}}_{1.6}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ using resonant soft x-ray diffraction and soft x-ray absorption spectroscopy at the Mn ${L}_{2,3}$ edge. The spin-flop transition is induced by an instability of magnetocrystalline anisotropy near a critical ${e}_{g}$ orbital configuration with a balanced occupation in ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ states, which contribute in-plane and out-of-plane orbital angular momenta, respectively. The magnetic field drives a certain change in the orbital occupation with lattice distortion to switch the magnetic anisotropy, resulting in the spin-flop transition. These results provide a comprehensive mechanism of interplay between spin, orbital, and lattice degrees of freedom to realize a low-field giant magnetoelasticity.