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Modifications in the structural and magnetic properties of co-precipitated cobalt ferrite nanoparticles can be accomplished by varying the annealing time periods during the synthetic process. Experimental results show that high-purity cobalt ferrite nanoparticles are obtained using a co-precipitation process. The dependence of the crystallite sizes on the annealing time was successfully demonstrated using XRD and SEM. Finally, vibrating sample magnetometer analyses show that the magnetic properties of the cobalt ferrite nanoparticles depend on their relative particle sizes.

IntisariKajian simulasi mikromagnetik magnetisasi reversal pada nano-dot magnetik dengan anisotropi tegak lurus telah dilakukan dengan menyelesaikan persamaan Landau-Lifshitz-Gilbert. Model yang disimulasikan nano-dot bahan magnetik pada unit sel Heat Assisted Magnetic Recording (HAMR) dengan dimensi 50 nm × 50 nm × 20 nm, 4πMS = 2500 gauss, TC = 373 K dan konstanta anisotropi K ⊥ = 5.10 5 erg/cm 3 . Simulasi ini dilakukan untuk mengetahui faktor-faktor fisis yang berpengaruh pada koersifitas dari pengamatan proses magnetisasi reversal. Hasil simulasi menunjukkan medan koersif meningkat sebesar 18% dengan penurunan redaman Gilbert dari α = 1 hingga α = 0,3. Akhirnya, peningkatan medan koesif juga teramati sebesar 32,7% dengan penurunan konstanta exchange stiffness dari A = 1.10 −6 erg/cm hingga A = 1.10 −7 erg/cm. ABSTRACTMicromagnetic magnetization reversal simulation study of magnetic nano-dot with perpendicular anisotropy has been performed by solving the Landau-Lifshiz-Gilbert equation. A model simulated is magnetic nano-dot materials as considering Heat Assisted Magnetic Recording (HAMR) cell units with dimensions of 50 nm × 50 nm × 20 nm, 4πMS = 2500 gauss, TC = 373 K and anisotropy constant K ⊥ = 5.10 5 erg/cm 3 . The simulation was conducted to determine physical factors that affect to coercive field. Simulation results show the coercive field increased by 18% with decreased Gilbert damping constant from α = 1 to α = 0.3. Finally, the increased of coercive field also observed by 32.7% with decreased exchange stiffness constant from A = 1.10 −6 erg/cm to A = 1.10 −7 erg/cm.KATA KUNCI: micromagnetic simulation, hysteresis curve, coercive field, HAMR I. PENDAHULUANKetersediaan bahan magnet dengan anisotropi magnetik tinggi, telah membuka peluang pemanfaatan yang semakin luas di industri teknologi informasi. Tidak hanya sebagai bahan dasar magnet permanen saja, karakteristik bahan yang stabil dengan panas telah membuka peluang pemanfaatan secara luas sebagai unit storage sel memori pada teknologi perekaman, yakni bahan magnet ini dapat diaplikasikan sebagai media perekaman. Artinya, bahan magnet dengan anisotropi tinggi ini tidak akan kehilangan karakter magnet ketika dipattern hingga orde nm akibat efek panas. Terlebih penemuan bahan magnet dengan anisotropi tegak lurus yang secara teori tidak ada pembatasan rasio dimensi sel dalam mem-pattern. Sedangkan teknologi HAMR diyakini sebagai salah satu metode read-write masa depan yang menggantikan teknologi media perekaman saat ini guna menghadirkan kera- * E-MAIL: bpurnama@gmail.com patan penyimpanan data hingga mencapai 10 Tbit/inch 2 [1, 2].Secara eksperimen, telah banyak dilaporkan berbagai metode untuk meningkatkan anisotropi yang terungkap dari besarnya nilai medan koersif ketika proses magnetisasi reversal. Namun demikian, peningkatan medan koersif belum diketahui secara pasti mekanisme. Secara umum, dua parameter fisika yang dianggap sebagai penyebab peningkatan nilai medan koersif domain wall pinning akibat ketidaksempurnaan struktur kristal penyusun la...

Using extraordinary Hall resistance (R H) measurements, the material dependence of thermally assisted magnetization reversal (TAMR) was investigated for microstructured multilayers of [Co (0.17 nm)/Pd (0.80 nm)] N with N ¼ 7 and 20, which exhibit markedly different magnetic properties. The threshold values of the external field (H w,th) necessary for controlling the magnetization direction in TAMR, obtained by direct application of a current pulse to the sample, were 220 Oe for the N ¼ 7 and 710 Oe for N ¼ 20 samples. The values of H w,th are found to be related to the magnetization saturation field at a critical temperature at which apparent coercivity decays.

We study the structural, electronic, and magnetic properties of the antiferromagnetic-layered oxyarsenide (LaO)­MnAs system from the first-principle calculation. The increasing Hubbard energy (U) in the Mn 3d orbital induces the increasing local-symmetry distortions (LSDs) in MnAs4 and OLa4 tetrahedra. The LSD in MnAs4 tetrahedra is possibly promoted by the second-order Jahn–Teller effect in the Mn 3d orbital. Furthermore, the increasing U also escalates the bandgap (E g) and the magnetic moment of Mn (μMn). The value of U = 1 eV is the most appropriate by considering the structural properties. This value leads to E g and μMn of 0.834 eV and 4.31 μB, respectively. The calculated μMn is lower than the theoretical value for the high-spin state of Mn 3d (5 μB) due to the hybridization between Mn 3d and As 4p states. However, d xy states are localized and show the weakest hybridization with valence As 4p states. The Mott-insulating behavior in the system is characterized by the E g transition between the valence and conduction d zx /d zy states. This work shows new physical insights for advanced functional device applications, such as spintronics.