Speaker
Description
Through neutron powder diffraction, we confirm the double perovskite Nd₂NiMnO₆ adopts a monoclinic P2₁/n structure with nearly complete B-site ordering of Ni²⁺ and Mn⁴⁺. Below T₁ = 198 K, magnetic susceptibility and neutron data reveal the Ni²⁺ and Mn⁴⁺ sublattices undergo ferromagnetic ordering, driven by strong 3d-3d exchange interactions. Upon cooling through T₂ = 22 K, a secondary transition occurs, where we discover an additional noncollinear, symmetry-breaking order of Nd³⁺ moments. We propose this rare-earth canting stems from the competition between f-d and f-f Heisenberg exchanges, finely balanced in the perovskite framework. The ground state symmetry also implies significant Nd³⁺ easy-plane anisotropy and a decoupling of the antiferromagnetic spin canting from the transition metal lattice.
Between T₁ and T₂, anomalous frequency-dependent ac susceptibility appears, characteristic of reentrant spin-glass-like behavior, attributed to antisite disorder and competing interactions. Furthermore, analysis of isothermal magnetization reveals magnetic entropy changes, suggesting potential for magnetic refrigeration. A peak entropy change of 2.25 J kg⁻¹K⁻¹ at T₁ under a 7 T field was observed. The scaling of this entropy, alongside other critical exponents, confirms the ferromagnetic transition at T₁ is a mean-field second-order phase transition. Collectively, our results provide crucial details on Nd₂NiMnO₆'s magnetism, reinforcing double perovskites as model systems for studying competing interactions, magnetocaloric effects, and reentrant spin-glass phenomena
| Session | Magnetism |
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