Surface‐Driven Magnetotransport in Perovskite Nanocrystals

Abstract

Unique insights into magnetotransport in 20 nm ligand-free La Sr MnO perovskite nanocrystals of nearly perfect crystalline quality reveal a chemically altered 0.8 nm thick surface layer that triggers exceptionally large magnetoresistance at low temperature, independently of the spin polarization of the ferromagnetic core. This discovery shows how the nanoscale impacts magnetotransport in a material widely spread as electrode in hybrid spintronic devices.

Versatile Molten Salt Synthesis of Manganite Perovskite Oxide Nanocrystals and Their Magnetic Properties

“…Manganite perovskite nanocrystals were synthesized by adapting a previously reported procedure that was dedicated to LSMO particles (Scheme 1) . The approach consists in triggering the reaction between nitrate salts of manganese (II) and of La, Pr, Sr or Ca into molten potassium nitrate (T fus =334 °C).…”

“…5 min. X‐ray powder diffraction (XRD) shows that LSMO nanoparticles were obtained at 600 °C, in agreement with our previous report (Figure ) . In the same conditions, substituting Sr with Ca to obtain LCMO and/or partially substituting La with Pr to obtain LPCMO do not yield pure phases but impurities of birnessite potassium manganese oxide K 0.2 MnO 2 ⋅xH 2 O, CaMnO 3 perovskite and La(OH) 3 (Figure S1 and Figure S2).…”

“…For LPCMO, the K content was below the detection threshold. According to previous data of atom‐scale chemical mapping, which could not detect K substitution into the LSMO nanocrystals, the most probable origin of the K content in LSMO and LCMO is surface contamination from the synthesis medium. Fast Fourier Transform Infrared spectroscopy (FTIR, Figure S4) shows for the three samples a broad band centered at 550 cm −1 , which corresponds to the stretching vibration of Mn−O in MnO 6 octahedra.…”

“…Manganites further exhibit a complex magnetic and magnetotransport behavior that can be tuned by appropriate substitution on the A site of the perovskite or by adjusting the size of the particles. This has translated into diverse studies in magnetism and magnetotransport in general …”

“…Faceted cobaltite particles were obtained the same way but at the submicronic scale . Our team reinvestigated recently the molten salt approach, by setting conditions for narrow size distribution and low density of crystal defects through a burst of nucleation triggered by large heating rates (Scheme ) . As a result, highly crystalline and faceted 20 nm nanocrystals of La 2/3 Sr 1/3 MnO 3 (LSMO) were designed.…”