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Among all bi-magnetic core(transition metal)@shell(transition metal oxide) nanoparticles (NPs), Ni@NiO ones show an onset temperature for the exchange bias (EB) effect far below the Néel temperature of bulk antiferromagnetic NiO. In this framework, the role played by the magnetism of NiO at the nanoscale is investigated by comparing the microstructure and magnetic properties of NiO and Ni@NiO NPs. With the aim of bridging the two systems, the diameter of the NiO NPs (~4 nm) is chosen to be comparable to the shell thickness of Ni@NiO ones (~2 nm). The EB effect in Ni@NiO NPs is attributed to the exchange coupling between the core and the shell, with an interfacial exchange energy of Δ E ~0.06 erg cm −2 , thus comparable to previous reports on Ni/NiO interfaces both in thin film and NP morphologies. In contrast, the EB detected in NiO NPs is explained in a picture where uncompensated spins located on a magnetically disordered surface shell are exchange coupled to the antiferromagnetic core. In all the studied NPs, the variation of the EB field as a function of temperature is described according to a negative exponential law with a similar decay constant, yielding a vanishing EB effect around T ~40–50 K. In addition, the onset temperature for the EB effect in both NiO and Ni@NiO NPs seems to follow a universal dependence with the NiO crystallite size. [ABSTRACT FROM AUTHOR]

Recently, potential technological interest has been revealed for the production of magnetocaloric alloys using Rare-Earth intermetallics. In this work, three series of Tb x R 1 − x Cu 2 (R ≡ Gd, La, Y) alloys have been produced in bulk and nanoparticle sizes via arc melting and high energy ball milling. Rietveld refinements of the X-ray and Neutron diffraction patterns indicate that the crystalline structure in all alloys is consistent with TbCu 2 orthorhombic I m m a bulk crystalline structure. The analyses of the DC-magnetisation ( M D C ) and AC-susceptibility ( χ A C ) show that three distinct degrees of disorder have been achieved by the combination of both the Tb 3 + replacement (dilution) and the nanoscaling. These disordered states are characterised by transitions which are evident to M D C , χ A C and specific heat. There exists an evolution from the most ordered Superantiferromagnetic arrangement of the Tb 0.5 La 0.5 Cu 2 NPs with Néel temperature, T N ∼ 27 K, and freezing temperature, T f ∼ 7 K, to the less ordered weakly interacting Superparamagnetism of the Tb 0.1 Y 0.9 Cu 2 nanoparticles ( T N absent, and T B ∼ 3 K). The Super Spin Glass Tb 0.5 Gd 0.5 Cu 2 nanoparticles ( T N absent, and T f ∼ 20 K) are considered an intermediate disposition in between those two extremes, according to their enhanced random-bond contribution to frustration. [ABSTRACT FROM AUTHOR]