Optimizing magnetic anisotropy of La_1−xSr_xMnO₃ nanoparticles for hyperthermia applications

Maximizing the magnetothermal response of magnetic nanoparticles (MNP's) for hyperthermia applications is a complex problem, because it depends sensitively upon interrelated magnetic and structural parameters. The task is somewhat simpler for systems with fixed composition, e.g. Fe₃O₄ or CoFe₂O₄, in which the particle size is the only means of modifying the magnetic anisotropy, and hence the magnetothermal response. In the La_1−xSr_xMnO₃ system however, the magnetic interactions as well as the particle size both change with the Sr concentration x, which makes it a much more complex system for which to optimize the hyperthermia response. We have investigated the effect of magnetic anisotropy on the magnetothermal response of La_1−xSr_xMnO₃ nanoparticles as a function of the particle size as well as the Sr concentration x where 0.20≤x≤0.45. The optimum particle size range is 25–30 nm for all concentrations, where the specific absorption rate (SAR) has a maximum. The linear response theory (LRT) has been applied to this system and good agreement has been found between the experimental and theoretically determined values of the SAR for samples lying in the single domain regime and having large enough anisotropy energies. The agreement is much better for the intermediate concentrations of 0.27 and 0.33, because of their large anisotropy as compared to other concentrations. It is concluded that the LRT can be successfully used to predict the SAR of these nanoparticles, provided they possess large enough effective anisotropies. Values of the ILP have been obtained for these samples and found to be comparable to those of magnetite and some commercial ferrofluids. - Highlights: • For La_1-xSr_xMnO₃ system, the magnetic anisotropy is determined not only by the particle size, but also by the strontium content x, we made a systematic study of both these parameters on its magnetothermal response. • Found profound effect of magnetic anisotropy on the magnetothermal response of La_1-xSr_xMnO₃ nanoparticles as a function of the particle size as well as Sr concentration x where 0.20≤x≤0.45. • The optimum particle size range is 25–30 nm for all concentrations, where the specific absorption rate (SAR) has a maximum. • Using the linear response theory (LRT) a good agreement was found between the experimental and theoretically determined values of the SAR for samples lying in the single domain regime. • The agreement becomes much better for the intermediate concentrations of 0.27 and 0.33, because of their large anisotropy constants as compared to other concentrations. • The intrinsic loss power was found to be comparable to that of magnetite and some commercial ferrofluids.