Tuning the structure, magnetization, and magnetoresistance of LSMO nanoparticles via sol–gel calcination

Abstract

Abstract This study focuses on the calcination temperature, between 600 and 1050 °C, used to prepare La 0.67 Sr 0.33 MnO 3 (LSMO) nanoparticles via a non-aqueous sol–gel method, with respect to their structure, magnetism, and magnetotransport properties. The X-ray diffraction and Rietveld refinement indicate phase-pure nanoparticles in a rhombohedral ( R -3 c ) structure. Moreover, they evidence the rise of the average size of crystallites from 31.9 to 111.4 nm with the lowest microstrain at about 900 °C. Magnetic measurements demonstrate that reduced surface disorder at increased temperatures enhances the saturation magnetization ( M ₛ) sixfold, increasing from 6.86 to 38.14 emu/g with the calcination temperature increase. However, the data indicate the transition in magnetic behavior: coercivity and remanence increase up to a maximum at 900 °C and then decline, marking the transition between single-domain and multi-domain behavior. Room-temperature magnetoresistance measurements identify an inverse dependence of the particle size on the magnitude of low-field magnetoresistance (LFMR)—larger particles have lower LFMR. The sample calcined at 600 °C, where intergranular spin-polarized tunneling occurs across many grain boundaries, has a very large LFMR of more than 95%. In contrast, for the 1050 °C sample, larger grain size allows better magnetic coherence and fewer boundary regions and, hence, it has a much weaker MR of about 40%. The findings show that calcination temperature is the main tuning knob for LSMO nanoparticles; it allows a predetermined balance between hard magnetic characteristics for magnetic components with high sensitivity in magnetoresistive devices for sensor applications.