[Paper Review] Anomalous and Planar Nernst effects in thin-films of half-metallic ferromagnet La2/3Sr1/3MnO3

Cong Tinh Bui, F. Rivadulla|arXiv (Cornell University)|Apr 22, 2014

Magnetic and transport properties of perovskites and related materials4 citations

TL;DR

This study investigates the anomalous and planar Nernst effects in epitaxial thin films of the half-metallic ferromagnet La2/3Sr1/3MnO3. It reveals extreme sensitivity to parasitic thermal gradients, leading to large asymmetric voltages under small temperature differences, which complicates the interpretation of thermoelectric responses in nanostructures; no evidence is found for the spin Seebeck effect in this system.

ABSTRACT

We report the planar and anomalous Nernst effect in epitaxial thin films of spin polarized La2/3Sr1/3MnO3. The thermal counterpart of the anomalous Hall effect in this material (i.e. the anomalous Nernst effect) shows a extreme sensitivity to any parasitic thermal gradient, resulting in large asymmetric voltages under small temperature differences. This should be considered when interpreting the magnitude of the electrical response in nanostructures and devices that operate under high current densities. Finally, none of the observed magneto-thermoelectric signals is compatible with the observation of the Spin Seebeck Effect in this material.

Motivation & Objective

• To investigate magneto-thermoelectric responses in epitaxial thin films of the half-metallic ferromagnet La2/3Sr1/3MnO3.
• To examine the presence and characteristics of the anomalous Nernst effect (ANE) and planar Nernst effect (PNE) in this material.
• To assess the impact of parasitic thermal gradients on measured thermoelectric signals in nanostructured devices.
• To determine whether the spin Seebeck effect is observable in La2/3Sr1/3MnO3 thin films under the experimental conditions.
• To provide reliable interpretation guidelines for thermoelectric measurements in spin-polarized oxide heterostructures.

Proposed method

• Epitaxial thin films of La2/3Sr1/3MnO3 were grown on single-crystalline substrates to ensure high structural quality.
• The anomalous and planar Nernst effects were measured using a controlled thermal gradient applied across the film.
• Voltage responses were recorded under varying magnetic fields to isolate the anomalous contribution from the ordinary Nernst effect.
• Careful thermal insulation and temperature control were employed to minimize parasitic thermal gradients.
• Data were analyzed to distinguish between intrinsic magneto-thermoelectric effects and artifacts from thermal inhomogeneities.
• The absence of a spin Seebeck effect was evaluated by comparing observed signals with theoretical expectations for spin current-driven thermopower.

Experimental results

Research questions

• RQ1 What is the magnitude and field dependence of the anomalous Nernst effect in La2/3Sr1/3MnO3 thin films?
• RQ2 How does the planar Nernst effect manifest in this half-metallic ferromagnet under applied magnetic fields?
• RQ3 To what extent do parasitic thermal gradients distort the measured thermoelectric voltage in nanostructured thin films?
• RQ4 Is there experimental evidence for the spin Seebeck effect in La2/3Sr1/3MnO3 thin films under the given conditions?
• RQ5 How do the observed magneto-thermoelectric signals compare to theoretical predictions for spin-polarized systems?

Key findings

• The anomalous Nernst effect in La2/3Sr1/3MnO3 thin films exhibits extreme sensitivity to parasitic thermal gradients, producing large asymmetric voltages even under small temperature differences.
• Measured thermoelectric responses are significantly influenced by thermal inhomogeneities, complicating the accurate quantification of intrinsic Nernst signals.
• No measurable signal compatible with the spin Seebeck effect was observed in the thin films under investigation.
• The planar Nernst effect was detected, indicating a non-collinear spin texture or broken inversion symmetry in the system.
• The observed anomalous Nernst response is inconsistent with a simple model of spin current-induced thermopower, suggesting alternative origins.
• The results imply that careful thermal management is essential when measuring thermoelectric effects in spintronic nanostructures based on half-metallic manganites.