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We report on the effects of annealing temperatures ranging from 225 °C to 325 °C on the magnetic properties of high aspect ratio iron oxide nanorods consisting of a ferrimagnetic Fe3O4 phase and an antiferromagnetic α-Fe2O3 phase in an as-prepared state. Annealing at the aforementioned temperatures under a constant flow of O2 for 3 h leads to an increment of the volume fraction of the antiferromagnetic α-Fe2O3 phase and concomitant enhancement of the crystallinity of the ferrimagnetic Fe3O4 phase. These opposing effects compete with each other, resulting in a decrease in global magnetization with increasing the annealing temperature. The desirable magnetic properties are achieved for the sample annealed at 250 °C. For all samples investigated, we observed an increase in low field magnetization at low temperatures after the sample is field cooled in the presence of a 1T magnetic field, which we attribute to the ordering of macro-spins of the weakly ordered antiferromagnetic α-Fe2O3 phase in the presence of the cooling field. Our study will pave the way for determining the optimal conditions to enhance the magnetic characteristics in iron oxide nanorods, which will enable its use in spintronics and biomedical applications. [ABSTRACT FROM AUTHOR]

We report on the magnetic properties of biphase iron oxide nanorods (NRs) consisting of ferrimagnetic Fe3O4 and antiferromagnetic α-Fe2O3 phases. Annealing as-prepared NRs at 250 °C for 5h, significantly improved the crystallinity of the Fe3O4 phase and enhanced the volume fraction of the α-Fe2O3 phase. Magnetometry data consistently reveal these two magnetically distinct phases, which are not in proximity to each other but separated by a region of disordered spins giving rise to enhanced magnetization at low temperatures when the sample was cooled down from 300 K in the presence of a 1T field to 10 K. This phenomenon which is also known as the pinning effect is much more pronounced in the annealed sample, resulting from the increased volume fraction of the α-Fe2O3 phase which could strengthen the interfacial spin frustration between these two phases and enhance the density of disordered spins at the interface. [ABSTRACT FROM AUTHOR]

A detailed study of the magnetic properties and heating capacities of electrodeposited FeCo nanowires with varying lengths (2-40 μm) and diameters (100 and 300 nm) is reported. We find that specific absorption rate (SAR) increases rapidly with increasing wire length up to 10 μm, followed by a gradual increase for larger lengths. Magnetic and hyperthermia measurements have revealed the important effect of dipolar interactions between the nanowires on their magnetic and inductive heating responses. Both calorimetric and AC magnetometry methods consistently show that the physical movement contribution of the nanowires to the SAR is small, and that for applied fields exceeding the coercive field, the nanowires tend to align parallel to the field, thus enhancing the SAR. Maximum SAR values of ~1500 W/g have been achieved for the largest wires at H=300 Oe and f=310 kHz. [ABSTRACT FROM AUTHOR]

Spherical and cubic exchange-coupled FeO/Fe3O4 nanoparticles, with different FeO:Fe3O4 ratios, have been prepared by a thermal decomposition method to probe anisotropy effects on their heating efficiency. X-ray diffraction and transmission electron microscopy reveal that the nanoparticles are composed of FeO and Fe3O4 phases, with an average size of ~20 nm. Magnetometry and transverse susceptibility measurements show that the effective anisotropy field is 1.5 times larger for the cubes than for the spheres, while the saturation magnetization is 1.5 times larger for the spheres than for the cubes. Hyperthermia experiments evidence higher values of the specific absorption rate (SAR) for the cubes as compared to the spheres (200 vs. 135 W/g at 600 Oe and 310 kHz). These observations point to an important fact that the saturation magnetization is not a sole factor in determining the SAR and the heating efficiency of the magnetic nanoparticles can be improved by tuning their effective anisotropy. [ABSTRACT FROM AUTHOR]

SrFe12O19/La1-xCaxMnO3 (SFO/LCMO) composites with x = 0.1 and 0.5 were synthesized via a two stage combined citrate precursor sol-gel and hydrothermal method. The structure and composition of the samples were refined from the X-ray diffraction patterns. The morphologies of the composites were investigated using transmission and scanning electron microscopies, which revealed micron-sized hexagonal platelets of SFO with LCMO particles with average diameters of 110-130 nm formed at the surface. An investigation of the temperature and field dependence of the magnetization found that the SFO phase with a ferrimagnetic characteristic up to 720 K dominates the magnetic properties of the composite samples. The SFO/LCMO composite samples showed a reduction in saturation magnetization and coercivity when compared with pure SFO. However, low temperature hysteresis loops recorded after cooling in applied fields up to 5 T revealed the absence of exchange bias in the SFO/LCMO composite, ruling out the possibility of significant interfacial magnetic coupling between SFO and LCMO. [ABSTRACT FROM AUTHOR]

Improving the sensitivity of existing biosensors for highly sensitive detection of magnetic nanoparticles as biomarkers in biological systems is an important and challenging task. Here, we propose a method of combining the magneto-resistance (MR), magneto-reactance (MX), and magneto-impedance (MI) effects to develop an integrated magnetic biosensor with tunable and enhanced sensitivity. A systematic study of the 7 nm Fe3O4 nanoparticle concentration dependence of MR, MX, and MI ratios of a soft ferromagnetic amorphous ribbon shows that these ratios first increase sharply with increase in particle concentration (0-124 nM) and then remain almost unchanged for higher concentrations (124 nM-1240 nM). The MX-based biosensor shows the highest sensitivity. With this biosensor, ∼2.1 × 1011 7 nm Fe3O4 nanoparticles can be detected over a detection area of 2.0 × 105 μm2, which is comparable to a superconducting quantum interference device biosensor that detects the presence of ∼1 × 108 11 nm Fe3O4 nanoparticles over a detection area of 6.8 × 104 μm2. The proposed biosensor can detect low and various concentrations of superparamagnetic nanoparticles (below 10 nm in size), which is of practical importance in biosensing applications. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles embedded in polymer matrices have excellent potential for electromagnetic device applications like electromagnetic interference suppression. We have synthesized polymer nanocomposites of poly(methylmethacrylate) doped with varying concentrations of iron nanoparticles (∼20 nm in size). The iron nanoparticles were produced using a microwave plasma technique and have a natural oxide surface layer for passivation. These nanocomposites were processed using melt blending technique. The polymer processing conditions were optimized to achieve good uniform dispersion of the nanoparticles in the polymer matrix. The concentration and dispersion of nanoparticles were varied in a controlled way. Surface characterization with scanning electron microscopy indicates that, to a large extent, the iron nanoparticles are embedded in the bulk; the surface mainly showed features associated with the polymer surface. Static magnetic properties such as susceptibility and M–H loops were studied using a physical property measurement system. The variation of the ferromagnetic response was consistent with the varying volume concentration of the nanoparticles, the polymer itself contributing a diamagnetic response. At room temperature, hysteresis loops exhibited a somewhat large coercivity (260 Oe) associated with a surface oxide layer on the particles. Overall, the excellent dispersion coupled with reasonable control over magnetic properties achieved in our experiments is promising for electromagnetic applications of these materials. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a comparative study of structural and magnetic properties of the as-grown and annealed samples of double perovskite, La2CoMnO6. The single monoclinic (P21/n) phase has been achieved for both the samples. Electron microscopy highlights the change in morphology of the as-grown and annealed samples, with the annealed sample having more grain boundaries and bigger particle sizes. The annealing in presence of oxygen leads to increase in the population of antiphase boundaries, which is supported by the decreases in the remanent and saturation magnetizations. An analysis of magnetization dynamics by means of AC susceptibility shows four different magnetic transitions, with two high temperature ferromagnetic transitions and two cluster glass-like states emerging at low temperatures, which appear almost identical in both the as-grown and annealed samples. [ABSTRACT FROM AUTHOR]

A comparative study of the magnetic softness, giant magnetoimpedance (GMI) effect, and microwave absorption capacity of glass-coated amorphous Co64.63Fe4.97B16Si11Cr3.4Ni0.02 and Co68B15Si10Mn7 microwires has been performed. We find that the Mn-containing sample exhibits a softer magnetic property, a larger GMI ratio, and a higher microwave absorption capacity as compared to those with a Fe-Cr-Ni composition. As a result, the Mn-containing microwire is shown to be a better microwave absorber for fabrication of a new class of microwave energy sensor based on Fiber Bragg Grating. Our study emphasizes a correlation between the magnetic softness, GMI, and microwave absorption in the microwires and paves the way to improving the performance of such sensors by tailoring their soft magnetic properties. [ABSTRACT FROM AUTHOR]

SrFeO3-δ belongs to the Ruddlesden-Popper class of systems exhibiting interesting electronic and magnetic properties. Ti4+-doped, oxygen-deficient SrFeO3-δ (SrFexTi1-xO3-δ; x=0.9 and 0.7) samples show canted antiferromagnetic spin ordering, in contrast to the undoped sample (x=1) which is known to exhibit a metallic behavior with a helical spin arrangement. ac susceptibility χac (f,T) at 10<=T<=300 K shows a frequency (100 Hz<=f<=10 kHz)-dependent temperature maximum, reminiscent of a spin-glass behavior. Increasing the Ti4+ content reduces the irreversibility, indicating a decrease in the frustration, which results in a diluted helical spin structure. Hysteresis loops can be associated with a gradual reorientation of spins in the field direction, indicating a canted type of spin arrangement. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of RuSr[sub 2]GdCu[sub 2]O[sub 8] with a magnetic ordering temperature (T[sub M]=135 K) and a resistively determined superconducting onset temperature (T[sub c]=45 K) were synthesized using a solid-state reaction. Transport and magnetic measurements indicated coexistence of weak ferromagnetic-like order and superconductivity at low temperatures. A novel radio-frequency (rf) resonant technique was employed to probe the mixed state response. The results clearly indicate that in the superconducting state (T

Provides information on a study that introduced an experimental method using radio frequency probes to study the dynamic magnetic properties and transverse susceptibility of nanostructures. Experimental details; Results and discussion on the study; Conclusion.

We report the synthesis and magnetic properties of core/shell FeO/Fe3O4 nanoparticles with an average size of 30 nm in a complex quasi-octopod shape. FeO nanoparticles were synthesized by a wet chemical synthesis route followed by partial oxidation to form core/shell structured FeO/Fe3O4 octopods. X-ray diffraction and transmission electron microscopy confirmed the presence of iron oxide phases and the formed core/shell FeO/Fe3O4 morphology. Magnetic measurements revealed two distinct temperatures corresponding to the thermally activated Verwey transition (TV ∼ 120 K) of the ferrimagnetic Fe3O4 shell and the Neel temperature (TN ∼ 230 K) of the antiferromagnetic FeO core. The nanoparticles exhibited a strong horizontal shift in the field-cooled hysteresis loop (the so-called exchange bias (EB) effect) accompanied by enhanced coercivity. The Meiklejohn-Bean model has been implemented to quantify the amount of frozen spins that locate at the interface between FeO and Fe3O4 and are responsible for the observed EB effect. [ABSTRACT FROM AUTHOR]

Ferrimagnetic and ferroelectric structures based on barium strontium titanate and barium hexaferrite are investigated for potential applications in tunable microwave devices. Thin film bilayers were grown on MgO and sapphire, and their underlying crystallographic, microstructural, and magnetic properties were analyzed and compared. Microcircuits were fabricated using optical lithography, and microwave properties and electrical tunability were measured in the range of 1–50 GHz. Overall, the studies demonstrate the possibility of realizing high quality multifunctional microwave materials that combine tunable magnetic and dielectric properties. [ABSTRACT FROM AUTHOR]

Presents a study which determined the switching behavior and strain dependence of the ferromagnet chromium dioxide thin films grown epitaxially on titanium oxide substrate. Investigation of the magnetic anisotropy and switching; Experimental procedure; Results and discussion.

Discusses a study which investigated the temperature and field dependence of the transverse susceptibility of a magnetic nanoparticle system. Characteristics of nanophase materials; Materials and methodology used; Results and conclusions.

The magnetic properties of superparamagnetic particles are influenced by the supporting matrix. We have systematically studied the DC magnetic properties of loosely packed manganese–zinc ferrite (Mn0.68Zn0.25Fe2.07O3) nanoparticles synthesized using a reverse micelle technique. The results have been compared with those for particles suspended in paraffin wax and embedded in a polypyrrole matrix. The polypyrrole-doped particles were prepared using an in situ ultraviolet irradiation method and spin-coated into thin films. The loosely packed particles showed no resolvable coercivity even well below the blocking temperature. On the other hand, the same particles in wax showed the opening up of a large coercivity below the blocking temperature. However, both the samples showed characteristic superparamagnetic transition peaks in the temperature-dependent susceptibility nearly at the same temperature. The particles in the polypyrrole matrix showed a remarkable increase in the blocking temperature and large hysteresis at 300 K. The structural characterization of the polymer-doped sample showed clustering of the nanoparticles. [ABSTRACT FROM AUTHOR]

We present a comparative study of structural and magnetic properties of the as-grown and annealed samples of double perovskite, La2CoMnO6. The single monoclinic (P21/n) phase has been achieved for both the samples. Electron microscopy highlights the change in morphology of the as-grown and annealed samples, with the annealed sample having more grain boundaries and bigger particle sizes. The annealing in presence of oxygen leads to increase in the population of antiphase boundaries, which is supported by the decreases in the remanent and saturation magnetizations. An analysis of magnetization dynamics by means of AC susceptibility shows four different magnetic transitions, with two high temperature ferromagnetic transitions and two cluster glass-like states emerging at low temperatures, which appear almost identical in both the as-grown and annealed samples. [ABSTRACT FROM AUTHOR]

SrFeO3-δ belongs to the Ruddlesden-Popper class of systems exhibiting interesting electronic and magnetic properties. Ti4+-doped, oxygen-deficient SrFeO3-δ (SrFexTi1-xO3-δ; x=0.9 and 0.7) samples show canted antiferromagnetic spin ordering, in contrast to the undoped sample (x=1) which is known to exhibit a metallic behavior with a helical spin arrangement. ac susceptibility χac (f,T) at 10<=T<=300 K shows a frequency (100 Hz<=f<=10 kHz)-dependent temperature maximum, reminiscent of a spin-glass behavior. Increasing the Ti4+ content reduces the irreversibility, indicating a decrease in the frustration, which results in a diluted helical spin structure. Hysteresis loops can be associated with a gradual reorientation of spins in the field direction, indicating a canted type of spin arrangement. [ABSTRACT FROM AUTHOR]