Finite-size scaling and exchange-bias in SrRuO3/LaNiO3/SrRuO3 trilayers

Abstract

We report a detailed magnetization study of the coherently strained trilayer heterostructures of metallic ferromagnet SrRuO3 (SRO)/paramagnetic-LaNiO3/SRO grown on a (001) oriented SrTiO3 single crystal substrate using the pulsed laser deposition technique. A tunable positive exchange bias (μoHEB ∼ 0.2 T, at 10 K) across the interface has been observed. Upon varying the SRO layer thickness (2 nm ≤ tSRO ≤ 18 nm), the saturation magnetization (MS ∼ 0.46 μB/Ru) increases significantly owing to electronic-reconstruction across the interfaces and finite size effects. The magnitude of μoHEB increases continuously with increasing tSRO and saturates above 16 nm; however, the loop-asymmetry increases rapidly as the temperature is lowered below the ferromagnetic Curie temperature (TC) of SRO. Notable reductions in both TC (125.6 K ≤ TC ≤ 146.4 K) and blocking temperature TB = T* (90.6 K ≤ T∗ ≤ 119.2 K) are observed due to surface effects that comply with the finite-size scaling law: TC(tSRO) = TC (∞) [1 − (ξo/tSRO)λ] with critical exponent λ = 1.12 ± 0.037 and correlation length ξ0 = 0.59 ± 0.02 nm signifying the fact that the investigated system is an intermediate between the 3D Ising configuration and those associated with mean field approximations.