PENGARUH KONSENTRASI Zn DAN SUHU SINTERING TERHADAP STRUKTUR KRISTAL, SIFAT MAGNETIK DAN ENERGI GAP NANOPARTIKEL Mn(1-x)Zn(x)Fe2O4 FERRITE

I PT TEDY INDRAYANA, Dr. Edi Suharyadi, M.Eng.

2016 | Tesis | S2 Ilmu Fisika

Nanopartikel spinel ferite Mn(1-x)Zn(x)Fe2O4 (x= 0,2 sampai x= 0,8) telah berhasil disintesis dengan metode kopresipitasi dan variasi suhu sintering 400, 600, 800, dan 1000 derajat celcius. Pola difraksi XRD mengkonfirmasi telah terbentuknya fasa spinel ferite Mn(1-x)Zn(x)Fe(2)O(4). Ukuran kristalit nanopartikel memiliki rentang nilai dari (15,2 plus-minus 0,2) nm hingga (30,0 plus-minus 0,2) nm, menunjukkan tren menurun dengan meningkatnya konsentrasi Zn karena penurunan konsentrasi ion Mn2+ yang berjari-jari ionik lebih besar. Peningkatan suhu sintering menghasilkan nanopartikel berukuran semakin besar dalam rentang (21,4 plus-minus 0,2) nm hingga (24,8 plus-minus 0,2) nm dikarenakan terjadinya pertumbuhan butir selama proses sintering. Parameter dan volume kisi kristal nanopartikel terkecil diperoleh ketika x = 0,5 dan terbesar ketika x = 0,6. Peningkatan suhu sintering menghasilkan tren kecenderungan penambahan parameter dan volume kisi kristal diikuti terjadinya redistribusi ion-ion nanopartikel. Citra TEM menunjukkan mikrostruktur dan morfologi butir nanopartikel mengalami perubahan akibat perlakuan sintering. Spektra FTIR mengkonfirmasi terjadinya serapan inframerah pada frekuensi 555,5 cm-1 sampai 586,4 cm-1 dan 416,6 cm-1 sampai 462,9 cm-1 yang mencirikan vibrasi peregangan simetrik antar kation dan anion masing-masing di subruang tetrahedral dan oktahedral. Hasil pengujian sifat magnetik pada suhu ruang mengkonfirmasi bahwa nanopartikel Mn1-xZnxFe2O4 bersifat ferrimagnetik lemah dengan koersivitas dalam rentang 41,5 Oe sampai 88,1 Oe menurun seiring peningkatan konsentrasi Zn dan cenderung meningkat dalam rentang 28,2 Oe sampai 154,5 Oe dengan peningkatan suhu sintering. Tren magnetisasi maksimum spesifik nanopartikel cenderung meningkat sampai x = 0,6; kemudian menurun hingga x = 0,8. Sampel nanopartikel Mn0,8Zn0,2Fe2O4 memiliki energi gap terkecil, yaitu 2,33 eV dan perlakuan suhu sintering 400oC untuk nanopartikel Mn0,5Zn0,5Fe2O4 menghasilkan energi gap terkecil, yaitu 2,11 eV. Konsentrasi Zn dan suhu sintering berpengaruh terhadap struktur kristal, energi gap, dan sifat magnetik nanopartikel.

Nanocrystalline mixed spinel ferrite of Mn(1-x)Zn(x)Fe2O4 (x= 0.2 to x= 0.8) have been successfully synthesized via coprecipitation method and sintered under different temperatures of 400, 600, 800, and 1000 degree celcius. The X-ray diffraction (XRD) patterns confirmed the formation of cubic spinel structure with some impurity phases. The crystallite sizes of nanoparticles were found in range of (15.2 plus-minus 0.2) nm to (30.0 plus-minus 0.2) nm and decreases by increasing Zn concentration due to the replacement of larger ionic Mn2+. Increasing sintering temperature gave larger crystallite size ranging from (21.4 plus-minus 0.2) nm to (24.8 plus-minus 0.2) nm due to the grain growth of nanoparticles because of thermal treatment. The lattice constant and cell volume of nanoparticles reduced to a minimum at x = 0.5 and attained maximum at x = 0.6 for Zn content. Sintering treatment gave an increase of nanoparticles lattice parameter. Those are attributed to the cation distribution caused by the change of ion composition and sintering temperature. The transmission electron microscope (TEM) image revealed that the microstructure and morphology of nanoparticles were change after sintering. The Fourier transform infrared spectroscope (FTIR) spectra also confirmed the existence of symmetric stretching vibration bands of metal ions around 555.5 cm-1 to 586.4 cm-1 and 416.6 cm-1 to 462.9 cm-1 in tetrahedral and octahedral sites, respectively. The room temperature magnetic measurement confirmed that sample nanoparticles were soft ferrimagnetic with coersivity decrease by increasing Zn content in range of 41.5 to 88.1 Oe and increase by increasing sintering temperature in range of 28.2 to 154.5 Oe. The specific maximum magnetization was found decrease with increase of Zn content up to x = 0.6 and back decrease until x = 0.8. Nanoparticles Mn0.8Zn0.2Fe2O4 was investigated have the smallest direct optical band gap of 2.33 eV and 2.11 eV belonged to Mn0.5Zn0.5Fe2O4 nanoparticles sintered at 400oC. Thus, the Zn concentration and sintering temperature strongly affect the crystal structure, optical gap energy, as well as magnetic properties of nanoparticles.

Kata Kunci : Concentration, crystal structure, gap energy, magnetic, sintering