Direct Imaging of the First Order Spin Flop Transition in the Layered Manganite La1.4Sr1.6Mn2O7

TL;DR

This paper reports the first direct imaging of a first order spin-flop transition in layered manganite La1.4Sr1.6Mn2O7, revealing ferromagnetic domain formation and nucleation processes linked to magnetic and transport properties.

Contribution

It provides the first direct visualization of ferromagnetic domain formation during the spin-flop transition in layered manganite, connecting microscopic magnetic structure with macroscopic behavior.

Findings

Ferromagnetic domains form at the spin-flop transition.

Nucleation occurs at crystal defect sites, not domain wall motion.

Magnetic hysteresis arises from domain nucleation and annihilation.

Abstract

Magnetic field induced transitions in the antiferromagnetic layered manganite La1.4Sr1.6Mn2O7 were studied using magnetization measurements and a high-resolution magneto-optical imaging technique. We report the first direct observation of the formation of ferromagnetic domains appearing at the first order spin-flop transition. The magnetization process proceeds through nucleation of polarized domains at crystal defect sites and not by domain wall motion. A small magnetic hysteresis is caused by the nucleation and annihilation of domains in the mixed state. These results establish a direct link betweeen the magnetic structure on the atomic scale as seen in neutron scattering and the macroscopic properties of the sample as seen in magnetization and conductivity measurements.