Ferromagnetic insulating epitaxially strained La2NiMnO6 thin films grown by sputter deposition

Abstract

The field of oxide spintronics can strongly benefit from the establishment of ferromagnetic insulators with near room-temperature Curie temperature. Here, we investigate the structural, electronic, and magnetic properties of epitaxially strained thin films of the double perovskite La2NiMnO6 (LNMO) grown by off-axis radio-frequency magnetron sputtering. We find that the films retain insulating behavior and a bulk-like Curie temperature in the order of 280 K independently of the epitaxial strain conditions. These results suggest a prospective implementation of LNMO films in multi-layer device architectures where a high-temperature ferromagnetic insulating state is a prerequisite.

Top‐Layer Engineering Reshapes Charge Transfer at Polar Oxide Interfaces

“…This scenario intuitively explains the presence of Mn 3+ also observed at the (less) polar LNMO//LSAT interface (Figure S3, Supporting Information). [ 19,28 ] Notice that all other investigated substrates constitute nonpolar interfaces with LNMO and therefore in these heterostructures we always observe a reduced amount of Mn 3+ compared to the STO and LSAT ones.…”

“…Structural characterization indicates epitaxial growth and high crystalline and surface quality in all the films (Figure S1, Supporting Information). [ 19 ] As shown in Figure a, films thicker than 30 uc (≈12 nm) exhibit bulk‐like ferromagnetic properties, that is, T C ≈ 270 K and saturation magnetization larger than 4 μ B /formula units. [ 19 ] However, the Curie temperature and the magnetization decrease as films are grown thinner.…”

“…[ 19 ] As shown in Figure a, films thicker than 30 uc (≈12 nm) exhibit bulk‐like ferromagnetic properties, that is, T C ≈ 270 K and saturation magnetization larger than 4 μ B /formula units. [ 19 ] However, the Curie temperature and the magnetization decrease as films are grown thinner. Still, 15 and 5 uc‐thick films display T C ≈ 250 K and T C ≈ 165 K, respectively.…”

“…From previous structural characterizations, we know that our relatively thick LNMO films grow with a prevalent rock‐salt ordering of Ni 2+ and Mn 4+ cations and display bulk‐like T C and saturation magnetization. [ 19 ] Therefore, we can exclude sub‐optimal growth conditions. It is known that in perovskite oxide films the formation energy of bulk oxygen vacancies is reduced with increasing tensile strain.…”

“…However, we cannot exclude the presence of additional Mn 3+ states present also in the top surface layer, as we previously detected in 30-uc-thick LNMO//STO heterostructures. [19] We also observe a small alteration of the Ni valence state (Figure 2b) to which we will come back.…”