Abstrak -Nanopartikel Nikel Ferit (NiFe 2 O 4 ) telah disintesis dengan metode kopresipitasi dengan memvariasi konsentrasi NaOH dan suhu sintesis. Struktur kristal, ukuran partikel, dan morfologi dari sampel dianalisa menggunakan X-ray diffraction (XRD) dan transmission electron microscopy (TEM). Ukuran butir pada konsentrasi NaOH 3,5,7;4,3; dan 4,2 nm, sedangkan pada suhu 60, 80, dan 150°C berturutturut adalah 4,2;4,9; dan 5,5 nm. Analisa fourier transform infrared (FTIR) menunjukkan dua puncak serapan pada rentang ~400-600 cm -1 yang terkait dengan site oktahedral dan tetrahedral pada struktur NiFe 2 O 4 . Sifat magnetik NiFe 2 O 4 hasil analisa vibrating sample magnetometer (VSM) menunjukkan bahwa sampel berperilaku ferromagnetik dengan nilai koersivitasnya pada rentang 42-47 Oe. Sampel dengan variasi konsentrasi NaOH, koersivitasnya cenderung menurun dengan menurunnya ukuran partikel. Sementara sampel dengan variasi suhu, semakin kecil ukuran partikel, koersivitasnya cenderung meningkat. Pada 15 kOe, nilai magnetisasi terbesar (6,17 emu/g) diperoleh pada sampel dengan rasio fasa α-Fe 2 O 3 paling rendah.Abstract -Nickel ferrite (NiFe 2 O 4 ) nanoparticles have been synthesized by co-precipitation method by varying concentration of NaOH and temperature of the synthesis. Crystal structure, grain size, and morphology of NiFe 2 O 4 nanoparticles were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The grain sizes with concentration of NaOH 3,5, and 10 M are 5.7; 4.3; and 4.2 nm, respectively, meanwhile for the temperature variations 60, 80, and 150 °C are 4.2; 4.9; and 5.5 nm, respectively. Fourier transform infrared (FTIR) analysis showed two absorption bands in the range of ~400-600 cm -1 related to octahedral and tetrahedral sites. The magnetic measurement using vibrating sample magnetometer (VSM) showed that the sample exhibited a ferromagnetic behavior with its coercivity in the range of 42-47 Oe. Samples with various concentration of NaOH showed that coercivity was decrease with the decrease of grain size. On the other hand, samples with various synthesis temperatures showed that coercivity was increase with the decrease of grain size. At 15 kOe, sample with the lowest phase ratio of α-Fe 2 O 3 has the highest magnetization (6.17 emu/g).

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