Produção Nacional
Revisado por pares
Griffiths-like phase, large magnetocaloric effect, and unconventional critical behavior in the NdSrCoFe O 6 disordered double perovskite
2022; American Physical Society; Volume: 106; Issue: 13 Linguagem: Inglês
10.1103/physrevb.106.134439
ISSN2469-9977
AutoresRomualdo S. Silva, C. Santos, M. T. Escote, B. F. O. Costa, N. O. Moreno, Simone Patrícia Aranha da Paz, Rômulo Simões Angélica, Nilson S. Ferreira,
Tópico(s)Electronic and Structural Properties of Oxides
ResumoA B-site disordered double perovskite $\mathrm{NdSrCoFe}{\mathrm{O}}_{6}$ was successfully synthesized by the conventional sol-gel method. Detailed experimental analyses revealed that $\mathrm{NdSrCoFe}{\mathrm{O}}_{6}$ crystallizes in the orthorhombic $Pnma$ space group, in which ${\mathrm{Co}}^{2+/3+}$ and ${\mathrm{Fe}}^{3+/4+}$ ions are randomly distributed at the BB\ensuremath{'} sites, and ${\mathrm{Sr}}^{2+}$ and ${\mathrm{Nd}}^{3+}$ ions are respectively ordered at the A and A\ensuremath{'} sites in an alternating arrangement along the $c$ direction. $\mathrm{NdSrCoFe}{\mathrm{O}}_{6}$ has a semimetallic-to-semiconducting transition nature, and a paramagnetic-ferromagnetic (FM) second-order phase transition originating from the complex hybridization between Co $3d$ and O $2p$ states is also found to occur at ${T}_{\mathrm{C}}\ensuremath{\approx}150$ K. Then the spin coupling between ${\mathrm{Fe}}^{4+}\ensuremath{\leftrightarrow}{\mathrm{Co}}^{3+}$ and ${\mathrm{Fe}}^{3+}\ensuremath{\leftrightarrow}{\mathrm{Co}}^{2+}$ randomly distributed on the B and B\ensuremath{'} sites leads to a FM cluster spin-glass behavior with characteristic parameters of $k=0.01, {T}_{\mathrm{SG}}=82.7$ K, $zv=1.89$, and ${\ensuremath{\tau}}_{0}=0.46\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ s. Additionally, Griffiths-like phase behavior was observed in the region ${T}_{\mathrm{C}}<T<{T}_{\mathrm{GP}}$, with ${T}_{\mathrm{GP}}=245$ K, consistent with the power law exponent of $\ensuremath{\lambda}=0.74$. The maximum isothermal magnetic entropy change $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{\mathrm{max}}\ensuremath{\approx}1.84\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{k}{\mathrm{g}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and relative cooling power $\ensuremath{\approx}43.8\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{k}{\mathrm{g}}^{\ensuremath{-}1}$ under a field of 40 kOe also indicate a magnetocaloric coupling wherein fitted critical exponents $\ensuremath{\beta}=1.384, \ensuremath{\gamma}=0.621$, and $\ensuremath{\delta}=1.421$ are far from any conventional universality class. Density functional theory calculations demonstrated spin short- and long-range ordering competitions for Fe/Co at BB\ensuremath{'} sites, which arise predominantly from the stronger negatively charged ligand interaction with Co $3d$ orbitals and the weakest Fe $3d$ orbitals. This unconventional behavior is expected to be the main reason for the experimentally observed magnetic exchange distance decreasing with $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.7}$.
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