Pressure Effects in Manganites with Layered Perovskite Structure

TL;DR

This paper theoretically investigates how hydrostatic pressure influences charge and spin dynamics in layered bilayer manganites by altering orbital states, which affects magnetic transitions and the material's dimensionality.

Contribution

It introduces a model showing how pressure-induced orbital stabilization impacts interlayer interactions and magnetic properties in layered manganites.

Findings

Pressure stabilizes the 3d_{x^2-y^2} orbital over 3d_{3z^2-r^2}.

Orbital changes weaken interlayer charge and spin couplings.

Pressure suppresses the three-dimensional ferromagnetic transition.

Abstract

Pressure effects on the charge and spin dynamics in the bilayer manganite compounds $La_{2-2x}Sr_{1+2x}Mn_2O_7$ are studied theoretically by taking into account the orbital degrees of freedom. The orbital degrees are active in the layered crystal structure, and applied hydrostatic pressure stabilizes the $3d_{x^2-y^2}$ orbital in comparison with $3d_{3z^2-r^2}$. The change of the orbital states weakens the interlayer charge and spin couplings, and suppresses the three dimensional ferromagnetic transition. Numerical results, based on an effective Hamiltonian which includes the energy level difference of the orbitals, show that the applied pressure controls the dimensionality of the spin and charge dynamics through changes of the orbital states.