Magnetic nanoparticles for space applications
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Magnetic nanoparticles for space applications S.K. Sharma1, Ravi Kumar2, S. N. Dolia3, V. V. Siva Kumar2 and, Mahavir Singh1 1 Department of Physics, H. P. University, Shimla-171005 India 2 Material Science Division, Nuclear Science Centre, New Delhi-110067 India 3 Department of Physics, University of Rajasthan, Jaipur 302004 India ABSTRACT Radiation resistant ferrite materials have potential applications in space station. Mg-Mn spinel ferrite was choosen for this study because of its radiation resistance and potential for use as an insulator in radiation environments. The radiation damage expected in these environments can be quickly and conveniently simulated using ion irradiation. The results of swift heavy ion irradiation induced modifications in the magnetization behavior of the Mg-Mn ferrite nanoparticles have been investigated using 100 MeV Ni8+ ion irradiation. To ensure the singlephase spinel structure of the system powder x-ray diffraction patterns has been performed. The powder samples were irradiated at three different fluences in the range 1x1012-5x1013 ions/cm2. Isothermal dc magnetization studies have been performed using SQUID and vibration sample magnetometer (VSM) on the pristine as well as on the irradiated samples at 20 K and 300 K. With irradiation saturation magnetization remains almost constant with ions irradiation. The coercivity values of the materials decreased about 5% with the fluence 1x1013 ions/cm2 as compare to the pristine nanoparticles. The results have been explained on the basis of the existence of surface defects produced by swift heavy ions, which generate orientational disorder of surface spins. The behavior of saturation magnetization with irradiations makes these nanoparticles suitable for memory devices in the space research. INTRODUCTION Swift heavy ion (SHI) irradiation is known to generate controlled defects of various types such as point/cluster and columnar defects in the materials [1] and has been studied extensively for the magnetic oxides and ferrites for last two decades [2-4]. SHI irradiation provides several interesting and unique aspects in the understandings of the damage structure and materials modifications. The swift heavy ions during their passage through the materials loose their energy by two processes; by inelastic collision with the electrons (electronic energy loss Se) and by elastic collisions with the nuclei (nuclear energy loss Sn). For high-energy heavy ions (MeV range), the electronic energy loss dominates over the nuclear energy loss. It is evident that the electronic energy loss Se is able to generate various types of defects such as point/clusters and columnar defects depending upon the magnitude of Se. To create columnar defects, certain threshold of Seth is required. If Se is less than the Seth it will create only point or clusters of defects. The SHI induced defects are known to create structural strain and disorder in oxide materials such as in CMR, high-Tc and magnetic oxides [5-7]. These structural strain and defects are responsi
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