La calorimetría diferencial de barrido y su aplicación a la Ciencia de Materiales

Se pone de manifiesto la idoneidad de la técnica de calorimetría diferencial de barrido para la caracterización de materiales. Se presentan ejemplos específicos de aplicación de dicha técnica en el estudio de los fenómenos ligados a la transición vitrea y cinética de cristalización de vidrios calcogenuros y metálicos así como en el estudio de la reordenación de fases desordenadas metastables

Exchange bias effects in Fe nanoparticles embedded in an antiferromagnetic Cr2O3 matrix

Powders consisting of ferromagnetic (FM) Fe nanoparticles, of about 7 nm in size, embedded in an antiferromagnetic (AFM) Cr2O3 matrix have been obtained by high-temperature reduction under a hydrogen atmosphere of a mixed Cr–Fe oxide. This FM–AFM system exhibits exchange bias effects, i.e. a loop shift (HE) and coercivity enhancement (ΔHC), when field-cooled through the N´eel temperature, TN, of Cr2O3. The exchange bias properties were measured as a function of temperature. HE and ΔHC are found to vanish at about TN(Cr2O3), indicating a good quality AFM matrix. Hence, high-temperature reduction of mixed oxides is demonstrated to be a suitable technique to develop new types of FM–AFM exchange-biased nanoparticles, from which novel applications of this phenomenon may be developed

La calorimetría diferencial de barrido y su aplicación a la Ciencia de Materiales

Se pone de manifiesto la idoneidad de la técnica de calorimetría diferencial de barrido para la caracterización de materiales. Se presentan ejemplos específicos de aplicación de dicha técnica en el estudio de los fenómenos ligados a la transición vitrea y cinética de cristalización de vidrios calcogenuros y metálicos así como en el estudio de la reordenación de fases desordenadas metastables

Magnetic interaction effects on the hard magnetic properties of ball-milled SmCo 5 + NiO and SmCo 5 + CoO composites: A M plot study

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Room-temperature coercivity enhancement in mechanically alloyed antiferromagnetic-ferromagnetic powders

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The coercivity,HC, and squareness of Co powders have been enhanced at room temperature by mechanically alloying them with antiferromagneticpowders with Néel temperature, TN, above room temperature. The enhancement is maximum after field annealing above TN. The existence of loop shifts and the dependence of HC on the annealing and measuring temperatures indicate that exchange bias effects are responsible for this behavior

Coercivity and squareness enhancement in ball-milled hard magnetic-antiferromagnetic composites

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The room-temperature coercivity,HC, and squareness, MR/MS (remanence/saturation magnetizations), of permanent magnet,SmCo5powders have been enhanced by ball milling with antiferromagnetic NiO (with Néel temperature, TN=590 K). This enhancement is observed in the as-milled state. However, when the milling of SmCo5 is carried out with an antiferromagnet with TN below room temperature (e.g., for CoO, TN=290 K), the coercivity enhancement is only observed at low temperatures after field cooling through TN. The ferromagnetic-antiferromagnetic exchange coupling induced either by local heating during milling(SmCo5+NiO) or field cooling (SmCo5+CoO) is shown to be the origin of the HC increase

Two-, three-, and four-component magnetic multilayer onion nanoparticles based on iron oxides and manganese oxides

Magnetic multilayered, onion-like, heterostructured nanoparticles are interesting model systems for studying magnetic exchange coupling phenomena. In this work, we synthesized heterostructured magnetic nanoparticles composed of two, three, or four components using iron oxide seeds for the subsequent deposition of manganese oxide. The MnO layer was allowed either to passivate fully in air to form an outer layer of Mn3O4 or to oxidize partially to form MnO|Mn3O4 double layers. Through control of the degree of passivation of the seeds, particles with up to four different magnetic layers can be obtained (i.e., FeO|Fe3O4|MnO|Mn3O4). Magnetic characterization of the samples confirmed the presence of the different magnetic layers

Synthesis of compositionally graded nanocast NiO/NiCo2O4/Co3O4 mesoporous composites with tuneable magnetic properties

A series of mesoporous NiO/NiCo2O4/Co3O4 composites has been synthesized by nanocasting using SBA-15 silica as a hard template. The evaporation method was used as the impregnation step. Nickel and cobalt nitrates in different Ni(II) : Co(II) molar ratios were dissolved in ethanol and used as precursors. The composites show variable degrees of order, from randomly organized nanorods to highly ordered hexagonally-packed nanowires as the Ni(II) : Co(II) molar ratio decreases. The materials exhibit moderately large surface areas in the 60-80 m2 g−1 range. Their magnetic properties, saturation magnetization (MS) and coercivity (HC), can be easily tuned given the ferrimagnetic (NiCo2O4) and antiferromagnetic (NiO and Co3O4) character of the constituents. Moreover, the NiCo2O4 rich materials are magnetic at room temperature and consequently can be easily manipulated by small magnets. Owing to their appealing combination of properties, the nanocomposites are expected to be attractive for myriad applications