Near room-temperature colossal magnetodielectricity and multiglass properties in partially-disordered La2NiMnO6 (1202.4319v2)

Abstract: We report magnetic, dielectric and magnetodielectric responses of pure monoclinic bulk phase of partially-disordered La2NiMnO6, exhibiting a spectrum of unusual properties and establish that this system intrinsically is a true multiglass with a large magnetodielectric coupling (8-20%) over a wide range of temperatures (150 - 300 K). Specifically, our results establish a unique way to obtain colossal magnetodielectricity, independent of any striction effects, by engineering the asymmetric hopping contribution to the dielectric constant via the tuning of the relative spin orientations between neighboring magnetic ions in a transition metal oxide system. We discuss the role of anti-site (Ni-Mn) disorder in emergence of these unusual properties.

• The paper demonstrates that controlled antisite disorder in La2NiMnO6 yields a colossal magnetodielectric effect of 8%-20% near room temperature with intrinsic multiglass characteristics.
• The paper employs the Pechini synthesis and Rietveld refinement to reveal a partially-disordered monoclinic structure that underpins both ferromagnetic and reentrant spin-glass transitions.
• The paper integrates density functional theory with experimental data to validate the coupling mechanism, informing strategies for advanced spintronic and multifunctional device applications.

Near Room-Temperature Colossal Magnetodielectricity in Partially-Disordered La$_2$NiMnO$_6$

This paper presents a comprehensive investigation into the magnetodielectric and multiglass properties of La$_2$NiMnO$_6$, noting its potential as a material with significant device applications due to its prominent properties near ambient conditions. La$_2$NiMnO$_6$ holds intrinsic multiglass characteristics, revealing a magnetodielectric coupling magnitude between 8% and 20% across a temperature spectrum between 150 K to 300 K.

Key Findings and Experiments

The synthesis of partially-disordered monoclinic La$_2$NiMnO$_6$ is achieved using the Pechini method, contrasted against previous reports of more ordered samples. Rietveld refinement analysis confirms the structure, revealing significant antisite disorder between Ni and Mn ions. This disorder plays a crucial role in influencing the material's unconventional properties.

Temperature-dependent field-cooled (FC) and zero field-cooled (ZFC) magnetization measurements illustrate a ferromagnetic phase transition at approximately 270 K, with a transition to a reentrant spin-glass state at lower temperatures. AC susceptibility analysis highlights a frequency-dependent peak below 150 K, suggesting dynamical magnetic behavior. Memory effects, characteristic of spin glass materials, further corroborate the reentrant spin-glass nature of the compound.

Dielectric constant measurements indicate significant relaxations attributed to both Maxwell-Wagner polarization and a Debye-type relaxation. Notably, the Debye contribution is intimately related to the asymmetrical hopping of charge carriers across Ni-Mn sites, a mechanism notably sensitive to spin orientations.

The complex interplay between magnetism and dielectric properties is further examined under magnetic fields up to 2 Tesla, establishing a notable magnetodielectric effect persisting above 100 K, with no significant magnetoresistance. This denotes an intrinsic coupling mechanism distinct from conventional magnetostrictive or electrostrictive models.

Theoretical Insights and Implications

First-principles calculations employing density functional theory provide additional insights, supporting the experimental findings by illustrating the energetic similarity between disordered and magnetically frustrated states within the compound. These confirmations of spin-phonon coupling inadequacy in explaining the substantial dielectric response align well with observed behavior.

The ramifications of this research are significant, suggesting potential pathways to engineer advanced magnetodielectric materials via controlled antisite disorder to optimize magnetic alignment and charge hopping mechanisms. Such innovations could profoundly impact future applications in spintronic and multifunctional device technologies.

Conclusion and Future Directions

The identification and characterization of La$_2$NiMnO$_6$ as an intrinsically multiglass system with sizable magnetodielectric properties broaden the scope for advanced functional materials designed for operational efficiency at near room-temperature conditions. The intricate role of antisite disorder in defining these properties beckons further inquiry into material synthesis methodologies to potentially tailor and enhance these properties for specific applications.

Future research could explore varying levels of disorder, dopant strategies, or structural modifications to expand the temperature range and coupling magnitudes. The insights provided here serve as a promising foundation for both theoretical exploration and empirical advancements in magnetodielectric systems.