Composition dependent magnetic properties of iron oxide - polyaniline nanoclusters

Gamma - Iron Oxide prepared by sol -gel process was used to produce nanocomposites with polyaniline of varying aniline concentrations. TEM shows the presence of chain like structure for lower polyaniline concentration. The room temperature hysteresis curves show finite coercivity of 160 Oe for all the composites while the saturation magnetization was found to decrease with increasing polymer content. ZFC - FC magnetisation measurements indicate high blocking temperatures. It is believed that this indicates a strongly interacting system, which is also shown by our TEM results. Monte Carlo simulations performed on a random anisotropy model with dipolar and exchange inteactions match well with experimental results.Comment: 9 (nine) pages, 6 figures (jpeg and eps

Crystallization induced ordering of hard magnetic L1₀ phase in melt-spun FeNi-based ribbons

The microstructure of newly developed hard magnetic Fe₄₂Ni₄₁.₃SixB₁₂-xP₄Cu₀.₇ (x = 2 to 8 at%) nanocrystalline alloy ribbons has been studied by transmission electron microscopy (TEM) and electron diffraction. A high-density polycrystalline grains, ∼30 nm in size, were formed in a ribbon after annealing at 673 K for 288 hours. Elemental mapping of the annealed specimen revealed the coexistence of three regions, Fe-rich, Ni-rich, and nearly equiatomic Fe-Ni, with areal fractions of 37%, 40%, and 23 %, respectively. The equiatomic L1₀-type ordered phase of FeNi was detected in between the Fe and Ni-rich phases. The presence of superlattice reflections in nanobeam electron diffraction patterns confirmed the formation of the hard magnetic L1₀ phase beyond any doubt. The L1₀ phase of FeNi was detected in alloys annealed in the temperature range of 673 to 813 K. The present results suggest that the order-disorder transition temperature of L1₀ FeNi is higher than the previously reported value (593 K). The high diffusion rates of the constituent elements induced by the crystallization of an amorphous phase at relatively low temperature (∼673K) are responsible for the development of atomic ordering in FeNi.Kazuhisa Sato, Parmanand Sharma, Yan Zhang, Kana Takenaka, and Akihiro Makino, "Crystallization induced ordering of hard magnetic L1₀ phase in melt-spun FeNi-based ribbons", AIP Advances 6, 055218 (2016) https://doi.org/10.1063/1.4952968

First principles based design and experimental evidence for a ZnO-based ferromagnet at room temperature

The introduction of ferromagnetic order in ZnO results in a transparent piezoelectric ferromagnet and further expands its already wide range of applications into the emerging field of spintronics. Through an analysis of density functional calculations we determine the nature of magnetic interactions for transition metals doped ZnO and develop a physical picture based on hybridization, superexchange, and double exchange that captures chemical trends. We identify a crucial role of defects in the observed weak and preparation sensitive ferromagnetism in ZnO:Mn and ZnO:Co. We predict and explain codoping of Li and Zn interstitials to both yield ferromagnetism in ZnO:Co, in contrast with earlier insights, and verify it experimentally

Co-occurrence of Superparamagnetism and Anomalous Hall Effect in Highly Reduced Cobalt Doped Rutile TiO2 Films

We report a detailed magnetic and structural analysis of highly reduced Co doped rutile TiO2 films displaying an anomalous Hall effect (AHE). The temperature and field dependence of magnetization, and transmission electron microscopy clearly establish the presence of nano-sized superparamagnetic cobalt clusters of 8-10 nm size in the films at the interface. The co-occurrence of superparamagnetism and AHE raises questions regarding the use of the AHE as a test of the intrinsic nature of ferromagnetism in diluted magnetic semiconductors.Comment: Physical Review Letters (In press