We study the magnetoimpedance effect, using a Co67Fe4Mo1.5Si16.5B11 amorphous, ribbon-based sensitive element, in the presence of a commercial Ferrofluid® liquid thin layer covering the ribbon surface. The magnetoimpedance response is clearly dependent on the presence of the magnetic ferroliquid, the value of the applied magnetic field, and the parameters of the driving current. The magnetoimpedance-based prototype is proposed as a biosensor with high sensitivity to the fringe field produced by magnetic nanoparticles. A special advantage of this sensor is its high stability to chemical aggressive media; hence, it can be used for in situ measurements during fabrication of biomaterials with a high level of affinity and specificity with nanoparticles employed as bimolecular labels.

Over the past two decades, magnetic hyperthermia and photothermal therapy are becoming very promising supplementary techniques to well-established cancer treatments such as radiotherapy and chemotherapy. These techniques have dramatically improved their ability to perform controlled treatments, relying on the procedure of delivering nanoscale objects into targeted tumor tissues, which can release therapeutic killing doses of heat either upon AC magnetic field exposure or laser irradiation. Although an intense research effort has been made in recent years to study, separately, magnetic hyperthermia using iron oxide nanoparticles and photothermal therapy based on gold or silver plasmonic nanostructures, the full potential of combining both techniques has not yet been systematically explored. Here we present a proof-of-principle experiment showing that designing multifunctional silver/magnetite (Ag/Fe3O4) nanoflowers acting as dual hyperthermia agents is an efficient route for enhancing their heating ability or specific absorption rate (SAR). Interestingly, the SAR of the nanoflowers is increased by at least 1 order of magnitude under the application of both an external magnetic field of 200 Oe and simultaneous laser irradiation. Furthermore, our results show that the synergistic exploitation of the magnetic and photothermal properties of the nanoflowers reduces the magnetic field and laser intensities that would be required in the case that both external stimuli were applied separately. This constitutes a key step toward optimizing the hyperthermia therapy through a combined multifunctional magnetic and photothermal treatment and improving our understanding of the therapeutic process to specific applications that will entail coordinated efforts in physics, engineering, biology, and medicine.

In this work an enhancement of the Curie temperature of the intergranular amorphous region in nanocrystalline alloys with respect to amorphous ribbons of the same composition is shown. The Curie temperature reaches a value of 125 C. The experimental results are discussed in terms of both an inhomogeneous distribution of Nb atoms in the interphase and the magnetic interactions between the Fe ferromagnetic grains and the matrix. Finally, it is proposed that the existence of a molecular field of about 80 T originated by the penetration of the exchange field of n-Fe nanocrystals into the amorphous paramagnetic intergranular region is the main cause of this Curie temperature enhancement. Moreover, the compositional dependence of the Curie temperature in Fe-8-Nb-Cu amorphous ribbons has been reported.

The possibility of tuning the magnetic behaviour of nanostructured 3d transition metal oxides has opened up the path for extensive research activity in the nanoscale world. In this work we report on how the antiferromagnetism of a bulk material can be broken when reducing its size under a given threshold. We combined X-ray diffraction, high-resolution transmission electron microscopy, extended X-ray absorption fine structure and magnetic measurements in order to describe the influence of the microstructure and morphology on the magnetic behaviour of NiO nanoparticles (NPs) with sizes ranging from 2.5 to 9 nm. The present findings reveal that size effects induce surface spin frustration which competes with the expected antiferromagnetic (AFM) order, typical of bulk NiO, giving rise to a threshold size for the AFM phase to nucleate. Ni 2+ magnetic moments in 2.5 nm NPs seem to be in a spin glass (SG) state, whereas larger NPs are formed by an uncompensated AFM core with a net magnetic moment surrounded by a SG shell. The coupling at the core-shell interface leads to an exchange bias effect manifested at low temperature as horizontal shifts of the hysteresis loop (∼1 kOe) and a coercivity enhancement (∼0.2 kOe). IntroductionThe steadily increasing interest in magnetic nanoparticles (NPs) over the past decade has been motivated by the unusual size-dependent magnetic behaviours and by their numerous applications in modern nano-electronics, magnetic separation or biomedical areas. [1][2][3][4][5][6][7] The growing research activity in this field has been propelled by the development of new chemical routes that allowed the synthesis of NPs with tuneable size distributions and being embedded in different insulating matrices. [8][9][10][11][12][13][14][15][16] It is worth noting that NPs of the same material and similar size but synthetized using different fabrication routes show a strong dependence of the magnetic properties on the morphology, microstructure or the nature of the matrix. 1,8,10,13 Moreover, 3d metal oxide NPs with different core-shell morphologies are also good candidates for a number of applications due to the possibility of tuning the magnetic response and/or the coating with a functional layer. 2,4,[13][14][15] Therefore, a comprehensive study combining advanced structural characterization techniques and meticulous magnetic measurements is needed to elucidate the microstructure-magnetism interplay at the nanoscale.Nickel oxide (NiO) has been under extensive research for decades due to its importance in numerous technological applications (i.e., catalysis, batteries, ceramics, etc.). Nowadays, nanosized NiO particles have generated a renewed interest because the combination of their unique properties (i.e., high surface area, short diffusional paths, exceptional magnetic properties, etc.) opens an avenue for their use in fields as diverse as catalysis, [17][18][19] anodic electrochromism, 20 capacitors, 21 smart windows, 22 fuel and solar cells 23,24 or biosensors. 25 Specially intense research effor...

The magneto-caloric effect (MCE) of arc-melted bulk and 10 h ball-milled nanostructured Pr2Fe17 powders has been investigated. The maximum value for the magnetic entropy change, |ΔSM|, in the milled alloy is 4.5 J kg−1 K−1 for μ0H = 5 T, at around room temperature. The full width at half maximum, δTFWHM, of |ΔSM|(T) for the nanostructured powders is about 60% greater than that of the starting bulk alloy, thus giving rise to large relative cooling power values of 573 J kg−1 (4.5 J cm−3) for μ0H = 5 T estimated from the product of |ΔSM|max × δTFWHM. These results have been compared with those of well-known magnetic materials that exhibit a large or giant MCE effect. The potential for using these low-cost iron based nanostructured Pr2Fe17 powders in magnetic refrigeration at room temperature is also discussed.