Noncollinear antiferromagnetism of coupled spins and pseudospins in the double perovskite La2CuIrO6

Abstract

We report the structural, magnetic and thermodynamic properties of the double perovskite compound La 2 CuIrO 6 from X-ray, neutron diffraction, neutron depolarization, dc magnetization, ac susceptibility, specific heat, muon-spin-relaxation (µSR), electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below ∼ 113 K, short-range spin-spin correlations occur within the Cu 2+ sublattice. With decreasing temperature, the Ir 4+ sublattice progressively involves in the correlation process. Below T = 74 K, the magnetic sublattices of Cu (spin s = 1 2 ) and Ir (pseudospin j = 1 2 ) in La 2 CuIrO 6 are strongly coupled and exhibit an antiferromagnetic phase transition into a non-collinear magnetic structure accompanied by a small uncompensated transverse moment. A weak anomaly in ac-susceptibility as well as in the NMR and µSR spin lattice relaxation rates at 54 K is interpreted as a cooperative ordering of the transverse moments which is influenced by the strong spin-orbit coupled 5d ion Ir 4+ . We argue that the rich magnetic behavior observed in La 2 CuIrO 6 is related to complex magnetic interactions between the strongly correlated spin-only 3d ions with the strongly spin-orbit coupled 5d transition ions where a combination of the spin-orbit coupling and the low-symmetry of the crystal lattice plays a special role for the spin structure in the magnetically ordered state.

Weak ferromagnetic insulator with huge coercivity in monoclinic double perovskite La2CuIrO6

“…A similar kind of double transition behavior is also observed for La 2 ZnIrO 6 [29]. This is consistent with previous result of P2 1 /n structure [34] but larger than that of P1 ̅ one [35]. Note that the obtained effective magnetic moment μ eff =2.…”

“…6. In earlier reports [34,35], it is found that the magnetization of La 2 CuIrO 6 system with both P1 ̅ and P2 1 /n structures exhibits a small but visible hysteresis loop with the coercivity H C equaling with the framework of short-range FM order. Particularly, a huge coercivity of H C~1 1.96 kOe at 10K is found, which is larger than ∼2.5 kOe, the highest value for hard magnetic ferrites, and is similar to a very recent YMn 0.5 Cr 0.5 O 3 system [44].…”

Correlated paramagnetism and interplay of magnetic and phononic degrees of freedom in 3d-5d coupled La2CuIrO6

“…(ii) Interestingly, below TN majority of the modes show anomalous softening till 40 K; however below ~ 40 K phonon frequencies become nearly constant. The temperature independent behaviour of phonon frequencies at low temperature (< 40 K ) may be due to the change in magnetic spin-structure and/or emergence of weak Ferromagnetic (FM) ordering as suggested in earlier transport studies [23]. The observed phonon softening below TN is found to be more pronounced for low energy phonon modes S1, S2, S3, S4 and S5 as 0.9, 0.3, 0.4, 0.7 and 0.4 % respectively, while for higher energy phonon modes (i.e.…”

“…La2CuIrO6 crystallizes in triclinic structure ( 1 P ; space group No. 2) [23]. Within triclinic phase…”

“…Ir 4+ (5d 5 ); pseudo-spin, j=1/2) oxidation state. Interestingly, spins are active in Cu sublattice and pseudo-spins in Ir sub-lattice and with lowering temperature intricate coupling between them gives rise to the long range Antiferromagnetic (AFM) ordering at TN ~ 74 K. It is observed that short range spin-spin correlation starts emerging within the Cu 2+ sub-lattice at temperature as high as ~ 113 K. At the same time there are some weak signature of correlation seen till temperature as high as ~ 180 K, indicating weak correlation within the paramagnetic (PM) phase [23]. Earlier studies have focused on the role of SOC, on-site interaction, inter-site hopping and probing their complex interplay [25][26][27], however, a detailed study deciphering the role of lattice degrees of freedom is lacking on this system.…”