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1.
RSC Adv ; 11(41): 25664-25676, 2021 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-35478869

RESUMO

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu1.5Mn1.5O4. The dynamic magnetic properties investigated using frequency-dependent ac magnetic susceptibility fitted using different phenomenological models such as Neel-Arrhenius, Vogel-Fulcher and power law, strongly indicate the presence of a cluster-glass-like behavior of Cu1.5Mn1.5O4 at 40 K. The magnetization data have revealed that our compound displays an occurrence of second-order paramagnetic (PM) to ferrimagnetic (FIM) phase transition at the Curie temperature T C = 80 K as the temperature decrease. In addition, the magnetic entropy change (ΔS M) was calculated using two different methods: Maxwell relations and Landau theory. An acceptable agreement was found between both sets of data, which proves the importance of both electron interaction and magnetoelastic coupling in the magnetocaloric effect (MCE) properties of Cu1.5Mn1.5O4. The relative cooling power (RCP) reaches 180.13 (J kg-1) for an applied field at 5 T, making our compound an effective candidate for magnetic refrigeration applications. The critical exponents ß, γ and δ as well as transition temperature T C were extracted from various techniques indicating that the magnetic interaction in our sample follows the 3D-Ising model. The validity of the critical exponents is confirmed by applying the Windom scaling hypothesis.

2.
RSC Adv ; 9(47): 27541-27548, 2019 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-35529229

RESUMO

Magnetic properties were studied just above the ferromagnetic-paramagnetic (FM-PM) phase transition of (Nd1-x Gd x )0.55Sr0.45MnO3 with x = 0, 0.1, 0.3 and 0.5. The low-field inverse susceptibility (χ -1) of Nd0.55Sr0.45MnO3 exhibits a Curie-Weiss-PM behavior. For x ≥ 0.1, we observe a deviation in χ -1(T) behavior from the Curie-Weiss law. The anomalous behavior of the χ -1(T) was qualified as Griffiths phase (GP)-like. The study of the evolution of the GP through a susceptibility exponent, the GP temperature and the temperature range of the GP reveals that the origin of the GP is primary due to the accommodated strain. Likewise, the magnetic data reveal distinct features visible only for x = 0.5 at a low magnetic field that can be qualitatively understood as the result of ferromagnetic polarons, entailed by the strong effect of chemical/structural disorder, whose concentration increases upon cooling towards the Curie temperature. We explained the magnetic properties at a high temperature for the heavily Gd-doped sample (x = 0.5) within the phase-separation scenario as an assembly of ferromagnetic nanodomains, antiferromagnetically coupled by correlated Jahn-Teller polarons.

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