Spin-up conversion, exchange-interactions, and tailored magnetic properties in core-shell La ₂ NiMnO ₆ of small crystallites

Abstract

La₂NiMnO₆-a ferromagnetic (FM) insulator offers tunable charge carriers and spins useful to devise its multiple properties and applications. In this view, we studied a core-shell La₂NiMnO₆(2-3 nm shell on 65 - 80 nm core) of a Ni²⁺/Ni³⁺(d⁷) to Mn⁴⁺/Mn³⁺(d⁴) spin-up conversion- revived a new FM phase-2, raising a spin-density<i>σ</i>_s = 0.7 s a^-¹over the Ni^2+/Mn⁴⁺species (phase-1),<i>σ</i>_s = 0.5 s a^-¹, i.e. 2.12<i>μ_B</i>/f.u. larger spin moment. HRTEM images studied with x-ray diffraction characterizing core-shell structure that plays a crucial role in tuning the high spin FM phase-2 of profound properties. Below 110 K, the dc magnetization and ac magnetic susceptibility<i>χ</i>(<i>ω</i>,<i>T</i>) reveal a metastable magnetic behavior on an antiferromagnetic canting of a spin-glass nature. The results follow a Vogel-Fulcher type relaxation with a relaxation time<i>τ</i>₀∼ 10^-13s, confirming a spin-glass freezing behavior. Uniquely, FM field of phase-1 controls magnetics of phase 2 of a coupled magnet, modulating joint features with small thermal magnetic hysteresis on heating-cooling cycles.