Telah dilakukan penelitian dengan proses High Energy Milling (HEM) SPEX 8000 selama 1,5 jam ; 4,5 jam ; 12 jam dan 20 jam terhadap serbuk Cobalt (Co) yang dicampurkan dengan serbuk Alumina (Al2O3). Perbandingan komposisi material tersebut adalah (36 : 64) (at%) sehingga terbentuk sistem komposit Co-Al2O3. Dihipotesakan bahwa sifat magnetoresistance (MR) dari bahan tergantung pada besarnya fasa Co-hcp dan fasa Co-fcc dari material tersebut. Konfirmasi dengan menggunakan peralatan four point probe, diperoleh harga MR 0,1 % ; 5,25% ; 5,3% dan 9,4% masing-masing untuk sistem komposit Co-Al2O3 pasca milling 1,5 jam ; 4,5 jam ; 12 jam dan 20 jam. Dimana sampel berbentuk pellet. Keberadaan fasa Co-hcp diketahui lebih dominan dibandingkan dengan fasa Co-fcc pada cuplikan awal bahan dasar cobalt. Diketahui pula dari pengukuran Vibrating Sample Magnetometer (VSM) harga saturasi magnetik bahan menunjukkan penurunan dari 116 emu/gram menjadi 36.1 emu/gram masing-masing untuk cuplikan pasca milling 1,5 jam sampai 20 jam. Hal ini menunjukkan bahwa proses milling membuat keberadaan fasa Co-hcp menurun dan fasa Co-fcc meningkat. Hasil-hasil di atas terlihat konsisten dengan hasil penelitian pada sistem Co-Al2O3 film tipis.

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There has been a study using High Energy Milling (HEM) SPEX 8000 for 1.5 hours, 4.5 hours, 12 hours and 20 hours to Cobalt (Co) dust mixed with Alumina (Al2O3) dust. Comparison of the composition material is (36 : 64) (at%), so at the end it will produce Co-Al2O3 composite system. It is assumed that magnetoresistance (MR) characteristic of the material depends on volume of Co-hcp phase and Co-fcc phase of the material. Confirmed by using four point probe device, it gains value of magneto resistance about 0.1 %, 5.25%, 5.3% and 9.4 % each for a basic material of Co-Al2O3 composite system after 1.5 hours, 4.5 hours, 12 hours and 20 hours milling process. The sample is in pellet shape. The existence of phases Co-hcp is known more dominant if we compare with Co-fcc phases on basic Cobalt. It is also defined that from magnetic saturation measurement Vibrating Sample Magnetometer (VSM) of the material, it shows a decline from 46.2 emu/ gram to 36.1 emu/gram of each basic material after 12 and 20 hours milling process. This shows that milling process makes Co-hcp phase decreases and Co-fcc increases. The statement above defines that there is a consistency with the research result on thin film Co-Al2O3 system.