Research articles Comparative study of the structural and magnetic properties of alpha and beta phases of lithium ferrite nanoparticles synthesized by solution combustion method Nygil Thomas a , Thooneri Shimna a , P.V. Jithin b , V.D. Sudheesh b,⇑ , Harish Kumar Choudhary c , Balaram Sahoo c , Swapna S. Nair d , N. Lakshmi e , Varkey Sebastian b a Department of Chemistry, Nirmalagiri College, Nirmalagiri, Kannur, Kerala 670701, India b Department of Physics, Nirmalagiri College, Nirmalagiri, Kannur, Kerala 670701, India c Materials Research Centre, Indian Institute of Science, Bangalore 560012, India d Department of Physics, Central University of Kerala, Kasaragod, Kerala 671314, India e Department of Physics, Mohanlal Sukhadia University, Udaipur, Rajasthan, 313001, India article info Article history: Received 11 February 2018 Received in revised form 4 May 2018 Accepted 5 May 2018 Available online 5 May 2018 abstract The structural and magnetic properties of lithium ferrite nanoparticles synthesized through the solution combustion route at different fuel to oxidizer ratio are studied using different techniques. Powder X-ray diffraction studies show that the fuel to oxidizer ratio is a critical parameter that determines the phase purity and degree of order of the samples. Magnetic studies show that the saturation magnetization and coercivity are comparable to those reported for lithium ferrites prepared using other methods. Saturation magnetization of Li0.8 sample at room temperature is 60 emu/g and is close to the bulk value. The hyper- fine parameters obtained from the Mössbauer spectra of Li0.6 and Li0.8 also match the reported values of phase pure samples. Mössbauer spectra of samples prepared at stoichiometric and fuel rich conditions show the presence of Fe 2+ cations in the ferrite phase, indicating that a reducing environment which reduces Fe 3+ to Fe 2+ ions is created as the fuel to oxidizer ratio is increased. The variation in the structural and magnetic properties of the samples, combined with TGA and FTIR studies, shows that the fuel lean condition is more appropriate for the direct formation of single phase lithium ferrite nanoparticles. Ó 2018 Elsevier B.V. All rights reserved. 1. Introduction Lithium ferrite has unique magnetic and electrical properties compared to other members of the spinel ferrite family [1–3]. The remarkable differences in properties make this material more interesting, both scientifically and technologically. Compared to other members in the spinel ferrite family, lithium ferrite has square hysteresis loop with high saturation magnetization and Curie temperature which creates the material suitable for the microwave device applications [2]. Lithium ferrite is an n-type semiconductor with high electrical resistivity makes the material a promising candidate for the gas sensing applications [4]. In addi- tion to this, lithium ferrite is also being used as cathode material in lithium ion battery and an alternate to Fe 3 O 4 in ferrofluid applica- tions [5,6]. Lithium ferrite has different types of polymorph struc- ture. Ordered lithium ferrite, which is also known as (a-LiFe 5 O 8 ) has the space group P4 3 32, in which tetrahedral sites are fully occupied by Fe 3+ ions and remaining Fe 3+ ions and Li + ions occupy 12d and 4b of octahedral sites in 3:1 ratio [7]. The disordered phase, (b-LiFe 5 O 8 ) has space group Fd3m in which lithium ions are randomly distributed over the octahedral sites [7,8]. The other polymorph structures such as c also exists but lithium ferrite com- monly crystallizes in a and b structures. Above 750 °C, lithium fer- rite undergoes a structural transition to b-LiFe 5 O 8 and on slow cooling it comes back to the ordered a-LiFe 5 O 8 phase. Quenching the sample from above 750 °C to room temperature gives the b- LiFe 5 O 8 phase [9]. Lithium ferrite is synthesized by different prepa- ration methods such as solid state reaction [10], sol–gel [11], com- bustion [12,13], spray pyrolysis [14], solvothermal [15] micro emulsion [16] etc. Many of these methods are time consuming and require high temperatures. It is reported that excess of lithium reactants are required in high temperature methods since lithium is highly volatile and leads to the formation of lithium deficient impurity phases also during high temperature synthesis [7]. Hence low temperature processing is of utmost importance in the synthe- sis of lithium ferrite. https://doi.org/10.1016/j.jmmm.2018.05.010 0304-8853/Ó 2018 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: sudheeshvd@gmail.com (V.D. Sudheesh). Journal of Magnetism and Magnetic Materials 462 (2018) 136–143 Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm