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Surabhi Shaji1 Nikhil Reddy Mucha1 A.K Majumdar1 Dhananjay Kumar1

1, North Carolina A&T State University, Greensboro, North Carolina, United States

The last few decades have seen a rapid increase in the energy product of permanent magnets mainly because of the inclusion of rare earth elements. 3d/4d structures involving heavy transition elements have long been known to possess good permanent magnetic properties because of their ability to induce large anisotropy in structures such as L10 magnets. However, the use of heavy transition metals such as palladium and platinum is very expensive. Thus, a comprehensive understanding and desire to develop other itinerant 3d/4d permanent magnets is of utmost importance to materials scientists. There have been reports which suggest that low content of Tantalum (W) has the potential to induce large magneto crystalline anisotropy and increase magnetization in iron (Fe) and cobalt (Co) as a result of large spin-orbit coupling of 4d elements which can lead to strong 3d/4d hybridization. Fe90Ta10 was arc-melted and used as target during pulsed laser deposition (PLD) experiments. The films exhibited enhanced coercivities (259.76 Oe) and saturation magnetization (425 emu/cm3). The effects of post annealing temperature, and deposition temperature on the magnetic properties in-plane and out-of-plane of the film was also investigated. The results have shown that the easy magnetization direction was in-plane which was structurally determined by x-ray diffraction to be (111). Deposition at room temperature followed by post-annealing at 400 C showed the highest coercivities. The anisotropy energy was calculated to be in the films deposited at room temperature, a value which is larger than many known ferromagnetic materials. We have also observed Extra-ordinary Hall Effect (EHE) effect in Fe-Ta films which establishes the scaling behavior of the extraordinary Hall constant, Rs. An involved analysis of high-resolution Hall (B, T) data recorded at temperature from 5 to 300 K shows that the scaling exponent, n in Rs ~ ρn, where ρ is the Ohmic resistivity, is ~ 1.1 ± 0.1. Theoretically, for homogeneous ferromagnets, n = 1 corresponds to Smit classical asymmetric scattering while n = 2 is attributed to the quantum mechanical side-jump scattering.

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