Exploring spin reorientation-induced magnetization reversal with inverse exchange bias effect and ab-initio DFT calculations on ferrimagnetic Gd2NiIrO6 iridates

초록

In this study, tunable bipolar magnetization reversal with an inverse exchange bias effect and magnetically switched magnetocaloric effect are reported in the hetero-tri-spin of a 3d-5d-4f based Gd2NiIrO6 (GNIO) polycrystalline sample. The sample was prepared using a conventional solid-state reaction method. Temperature (T)- dependent direct current (DC) and alternating current (AC) magnetic susceptibility studies revealed that GNIO exhibits ferrimagnetic (FiM) behavior below the transition temperature T-N similar to 164 K owing to the Ni2+- O2- - Ir4+ superexchange interactions. With the application of 500 Oe, low-field-cooled (HFC) induced magnetization reversal (MR) below the compensation temperature (T-comp) similar to 28 K, and a spin re-orientation (SR) like behavior at T-SR similar to 96 K were observed in FC mode within the temperature region of T-comp < T-SR < T-N. T he observed negative magnetization across the magnetic compensation could be attributed to the competing magnetic interactions arising from the thermal variations in the magnetic moments of the Gd and Ni-Ir sublattices. An inverse exchange bias effect was observed from isothermal magnetization measurements, where the M(H) loop shifted after field- cooling (H-FC). The H-assisted magnetization switching confirmed the spin reversal phenomenon, and temperature-dependent magnetic entropy changes complemented both the conventional and inverse magneto- caloric effects. Density functional theory (DFT) calculations employing the generalized gradient approximation (GGA) and the Hubbard U model along with spin-orbit coupling confirmed that the FiM phase is the most stable magnetic state for GNIO. This finding is in good agreement with the experimental observations. Interestingly, the calculated spin-polarized density of states revealed a dominant contribution of Ird over Nid near the Fermi level, confirming the Mott-insulating behavior of GNIO.

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