Comparative studies are presented of iron oxide nanoparticles in the 7ââ?¬â??15nm average diameter range ball milled in hexane in the\r\npresence of oleic acid. Transmission electron microscopy identified spherical particles of decreasing size as milling time and/or\r\nsurfactant concentration increased. Micromagnetic characterization via MÃ?¨ossbauer spectroscopy at room temperature yielded\r\nbroadened magnetic spectroscopic signatures, while macromagnetic characterization via vibrating sample magnetometry of 7-\r\n8 nm diameter particles showed largely superparamagnetic behavior at room temperature and hysteretic at 2K. Zero-field and\r\nfield-cooled magnetization curves exhibited a broad maximum at ~215K indicating the presence of strong interparticle magnetic\r\ninteractions.The specific absorption rates of ferrofluids based on these nanoparticle preparations were measured in order to test\r\ntheir efficacies as hyperthermia agents
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