High-Pressure Synthesis of Lu₂NiIrO₆ with Ferrimagnetism and Large Coercivity

Abstract

Double-perovskite Lu 2 NiIrO 6 was synthesized at high pressure (6 GPa) and high temperature (1300 °C). Synchrotron powder X-ray diffraction indicates that its structure is a monoclinic double perovskite (space group P2 1 /n) with a small, 11% Ni/Ir antisite disorder. X-ray absorption near-edge spectroscopy measurements established Ni 2+ and Ir 4+ formal oxidation states. Magnetic studies indicate a ferrimagnetic transition at 207 K. The lowtemperature magnetization curve of Lu 2 NiIrO 6 features broad hysteresis with a coercive field as high as 48 kOe. These results encourage the search for hard magnets in the class of 3d/5d doubleperovskite oxides.

Large Magnetocrystalline Anisotropy and Giant Coercivity in the Ferrimagnetic Double Perovskite Lu2NiIrO6

“…The magnetic moment and magnetic susceptibility obtained by Monte Carlo simulations for our Heisenberg model are plotted as a function of the temperature in Figure . When only J 1 and J 2 are taken into consideration, we find a Curie temperature of 235 K. When J 1 to J 4 are taken into consideration, the Curie temperature is reduced to 220 K, which is close to the experimental value of 207 K …”

“…The magnetic moment and magnetic susceptibility obtained by Monte Carlo simulations for our Heisenberg model are plotted as a function of the temperature in Figure 3. When only J 1 and J 2 are taken into consideration, we find a Curie temperature of 235 K. When J 1 to J 4 are taken into consideration, the Curie temperature is reduced to 220 K, which is close to the experimental value of 207 K. 43 Since for iridates, particularly those containing Ir 4+ (5d 5 ) ions, SOC drives many novel phenomena, 7,8,49 we next include it in our calculations. Remarkably, SOC without an onsite Coulomb interaction does not provide a finite band gap (Figure 4a,b).…”

“…We consider the onsite Coulomb interaction for the Ni 3d (5 eV) and Ir 5d (4 eV; the linear response approach results in a value of 4.47 eV) orbitals (GGA+ U method) as well as the SOC (GGA+SOC and GGA+ U +SOC methods). The experimental lattice parameters are employed: Lu 2 NiIrO 6 is monoclinic (space group P 2 1 / n ) with β = 90.183° and lattice constants a = 5.214 Å, b = 5.635 Å, and c = 7.539 Å. A plane-wave cutoff energy of 90 Ry is used in the wave function expansion together with a 640 Ry cutoff of the augmentation charge.…”

“…While many iridates with pyrochlore, ,− honeycomb lattice, − and perovskite − structures were explored in detail and the magnetic properties are largely understood, for the double perovskite A 2 BIrO 6 ,,− the involvement of various comparable energy scales complicates the situation. For instance, monoclinic Lu 2 NiIrO 6 (space group P 2 1 / n ), which can be synthesized under high temperature and pressure, shows experimentally ferrimagnetic (FiM) ordering with an unclear magnetic nature of the Ir 4+ ions and giant coercivity (coercive field as high as 48 kOe), which calls for clarification due to potential applications in hard magnets and spintronics. A recent theoretical study finds no significant impact of the SOC on the electronic properties .…”

Tl2Ir2O7: A Pauli Paramagnetic Metal, Proximal to a Metal Insulator Transition

“…CuIrO 6 44,45. For clarification, the spectrum of Tl 2 Ir 2 O 7 is shown on an expanded scale in the inset of Figure2asuperimposed with the spectra of ∼Ir 5+ (d 4 ) standards, where the standard spectra were shifted to compensate for the chemical shift and rescaled for superposition.…”