Journal of New Technology and Materials
Volume 8, Numéro 1, Pages 42-47
Authors : Hamdi Trabelsi.
The present paper reports detailed structural, magnetic and magnetocaloric characterizations of the charge ordered Nd0.5Ca0.4M0.1MnO3 (M=Na, K : NCNMO and NCKMO) polycrystalline samples. Our compounds were synthesized using the solid state reaction at high temperature. Both samples are single phase and crystallize in the orthorhombic structure with Pnma space group. NCNMO (⟨r_A ⟩ = 1.1775 Å) undergoes a charge disordering transition (CO) associated to the paramagnetic (PM)-antiferromagnetic (AFM) phase transition at T < 250 K. The long range AFM ordering seems to from at 35 K, rather than 150 K as previously reported. In the intermediate temperature range, charge ordering occurs while orbital ordering sets in progressively, with no magnetic order. For NCKMO sample (⟨r_A ⟩ = 1.2085 Å), K doping induces the melting of the CO state and the presence of the short-range AFM phase, which is metastable and transforms into the stable ferromagnetic (FM) state. Magnetic characterization shows the signature of AFM-FM ordering and spin-glass coexisting at low temperature. The temperature dependence of magnetic entropy change at high magnetic field values presents some anomalies attributed to the metamagnetic transition, which is of first order.
Manganites; Structure; Charge ordering; Magnetocaloric effect.
محمد ولد دالي.
Benkamla Mohamed Abdelaziz.