International Journal of Computer Applications (0975 – 8887) Volume 48– No.15, June 2012 10 Electro Paramagnetic Resonance Studies to Determine the Dopant Site Occupancy of Dy-Sm doped Magnesium Ferrite for Micro Strip Patch Antenna Substrate Vasant Naidu Professor/ECE Sethu Inst. of Tech., Pulloor – 626115, Tamilnadu, India S. Gayathri Devi Asst Professor/ECE Sethu Inst. of Tech., Pulloor – 626115, Tamilnadu, India R. Legadevi Research Asst Sethu Inst. of Tech., Pulloor – 626115, Tamilnadu, India Lakshmi Priya Asst Professor/ECE Sethu Inst. of Tech., Pulloor – 626115, Tamilnadu, India ABSTRACT In the present study, site occupancy of Dysprosium (Dy), Samarium(Sm) doped Magnesium ferrite were investigated by electro paramagnetic resonance (EPR). Point charge calculations were used to predict the EPR spectrum of each lanthanide in A- and B-sites. Different EPR spectra are expected for A- versus B-site substitution when Sm 3+ and Dy 3+ are the dopants. The experimentally observed doping behavior of Dy 3+ –Sm 3+ in MgFe 2 O 4 suggests that as a Sm 3+ cation it is on the A-site. EPR signal intensity suggested the amphoteric behavior due to Dy 3+ in the magnesium ferrite material as Dy 3+ was found to be a B-site dopant. These studies will be helpful for the analytical studies of permittivity and permeability to design Microstrip patch antenna to be used in pervasive computing. Keywords: EPR, Dy-Sm Doped Magnesium ferrite, Dopant site. 1. INTRODUCTION In an interesting review [1], electron paramagnetic resonance (EPR) is listed among the less developed methods for quantitative determination of site occupancies. However, for most transition metals and for rare earth ions that are present only in small amounts (up to about l% per site), it still is the most powerful method. That is because this method gives unambiguous information about the valence state and site symmetry, and, at least for some ion. Magnesium ferrite, doped with lanthanide (Dy- Sm) ions, has found its use as a multilayer dielectric substrate [2]. It was observed that, certain lanthanides, such as Ho, Dy, Sm and sometimes Er, can improve the resistance of the magnesium ferrite due to electrochemical or time dependent failure, when fired in low oxygen partial pressures[3]. It is already mentioned that ―magic‖ dopants can choose their site occupancy as a result of the local Mg/Fe ratio and oxygen partial pressure during firing[4] and since these dopants were also termed ―amphoteric‖ due to the site change of a well defined valence dopant and causing a change of the relative charge[5]. Here EPR studies are used to investigate a series of lanthanide-doped magnesium ferrite, with the chief aim for determining the site occupancy of these lanthanides. To facilitate the detection of amphotericity, these studies for the samples that are either magnesium-rich or ferrite-rich (Mg/Fe) 1.01 or 0.99, respectively). The Mg-rich samples will drive amphoteric dopants to more frequently occupy B-sites, where as Fe-rich samples will drive such dopants more frequently into the A-sites. To determine the cubic crystalline electric field parameters for both A- and B-site locations for each particular lanthanide dopant, the analytical calculations for the point charge model is being considered Prediction of the fundamental lowest energy level of the 3 + lanthanide in both types of site becomes possible. This then allows to assess whether A- or B-site dopant locations will have different EPR spectra [6]. 2. THEORY, THEORETICAL RESULTS, AND DISCUSSION It is seen that the interaction with the crystalline electric field is much weaker than the spin-orbit coupling for the lanthanide ions [7]. There a sum of all interactions is expressed as a Hamiltonian  =   +   +   +   +  ℎ where H fi + H so >> H cf >> H z + H hf , H fi is the Hamiltonianof the free ion, Hso is the spin-orbit Hamiltonian, Hcf is the crystal field Hamiltonian, H z is the Zeeman Hamiltonian, and H hf is the hyperfine Hamiltonian. The action of the crystal field upon the free ion can partially remove the degeneracy from among the various Ґ i states.Therefore the crystalline electric field is a perturbation on the 2J + 1 degeneracy of the free-ion ground state. Here C4,k and C6,k are constants, unique to each type of coordination sphere; r4 and r6 are the fourth- and sixth- order ionic radii; r k is the radius of the coordination sphere (distance from the dopant to an ion in the sphere ) Z k is the charge of an ion in the coordination sphere. The terms b4 and b6 can then be found by summing b4,k and b6,k over all possible shells. Because we are performing these calculations for two different lanthanides, it is useful to factor out all the lanthanide-specific parameters that do not change as a function of k. This yields where and where From the equations set forth by Bureau et al.,[8] it can be shown that the constants C4,k and C6,k can be evaluated according to the following expressions and where N is the total number of ions, i, in each shell, k, and Yl m(õi,_i) is a spherical harmonic.