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Acicular T-Fe20 particles surface coated with barium ferrite fBF) have been prepared by reacting acicular U-FeOOH and the surface adsorbed Ba++ at 810 to 89OoC followed by reduction-oxidation. has a diameter of 100 to 2 0 0 nm and aspecz ratio of 3 to 8, a coercivity of 330 to 3600 Oe, a saturation and residual magnetization of 47 to 70 and 23 to 34 emulg, respectively, by controlling the Ba++ concentration and heat treatment temperatures. They have an extremely low temperature coefficient of coercivity of -0.07 to -0.1 %/OC. These particles are potentially useful for high density recording purposes.The BF coated r-Fe20

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Abs&m%-(Co,Mn) modifled 7-Fe203 thin lllmr with M In-plane coerclvIt of 2200 to 4008 oe, a saturntion n,ngneti;cPtion of 250 to 310 emdcm{ and a 4wrenerr ratio of 0.6 to 0.83 were prepared by DCreactive magnetron sputtering. The fllau were deposited onto Si(100) and co&g #7059 glau substrata h M oz/Ar atniorphere by using plluy compodte tnrgek Composition adJustment, reductlan-oxidation nnd pootannealing trenbients were found to amect coercivity as weU as other magnetk properlies In dlfTerent extents. owing to their sound mngnetic perfonwace, these are pronrlsing for appllcatlow in high density ningnetic recording.

High resolution TEM (HRTEM), Mössbauer spectroscopy and SQUID magnetometry were utilized to study the fine structure of equiaxed, Mn- and Co-doped γ-Fe2O3 nanocrystals with a particle size of 30–50 nm. The allocation of cation distribution, based on a redox mechanism and known cation site preferences is (Mn2+0.11Fe3+0.89) [Mn4+0.07Mn3+0.16) Co2+0.34Fe3+1.23⧠0.20]O4, in which ⧠ is the vacancy, (⋅⋅) is the A site, and [⋅⋅] is the B site. This leads to an Fe occupancy ratio of B sites to A sites of 1.38, as verified by Mössbauer spectroscopy. The calculated saturation magnetic moment of 2.99μB/MF is very close to the measured 2.84μB/MF. HRTEM micrographs of the air-cooled nanocrystals fits well with the simulated lattice images using the proposed cation distribution (without directional ordering). While the HRTEM micrograph of the core of an annealed nanocrystal are not in good agreement. This is thought to arise from directional ordering inside the annealed particles.