Cobalt ferrite (CoFe2O4) thin films were epitaxially grown on (001) SrTiO3 and (001) MgO by laser molecular beam epitaxy. Microstructural studies indicate that the CoFe2O4 grown on (001) SrTiO3 with compressive strain are c-oriented island growth mode with rough surface morphology, whereas the films on (001) MgO with tensile strain become c oriented with layer-by-layer mode. Magnetic property studies reveal that the compressive strained CoFe2O4 films on (001) SrTiO3 can significantly enhance out-of-plane magnetization (190emu∕cm3) with a large coercivity (3.8kOe). In contrast, the tensile strained CoFe2O4 films on (001) MgO exhibit weak magnetic anisotropy. These results suggest that strong magnetic anisotropy is highly dependent on the lattice mismatch induced strain.

The magnetic, structural, and transport properties of single-layer magnetite (Fe3O4) films prepared by reactive sputtering were investigated. Magnetoresistance (MR) was measured at various thicknesses and temperatures. The increase in MR with thickness is related to grain crystallinity and size, as confirmed by transmission electron microscopy. MR arises from intergranular tunneling, which is supported by the temperature dependence of resistivity (logρ∼T−1∕2). Field-dependent MR correlates with the M curve. Magnetoresistance versus magnetization curves clearly show that the MR effects come from the surface spin arrangement near the grain boundaries. The dependence of MR on the magnetic field observed in polycrystalline Fe3O4 films can be attributed to a surface magnetization near the grain boundary, which will be discussed.

With the miniaturization of magnetic technologies, the need to understand magnetization on length scales below a micron is becoming increasingly important. This booming interest in micro magnetics has fueled a renaissance in both micro-magnetic modeling and measurement techniques. Conversely, the codevelop-ment of modeling and imaging has made possible recent advances in this critical area of magnetism. On the modeling side, the rapid development of high-speed computing has had a tremendous impact on micromagnetics simulations. On the measurement side, a number of microscopies have been developed for imaging on a length scale of tens of nanometers. Figure 1 shows an image of rows of bits in a magneto-optical medium. The bits were both written and imaged using a magnetic force microscope. Results on this length scale provide information that can be used in models and also challenge models’ predictive capabilities. The image on the cover of this issue shows naturally occurring domain patterns in a single-crystal ferrite, a system that exhibits extremely complex magnetic stmctures.

A tunneling-type magnetoresistance (MR) as large as 158% is observed at T = 300 K in a polycrystalline Zn0.41Fe2.59O4 sample, in which the Zn0.41Fe2.59O4 grains are separated by insulating alpha-Fe2O3 boundaries. The huge room-temperature MR is attributed to the high spin polarization of Zn(0.41)Fe(2.59)O4 grains and antiferromagnetic correlations between magnetic domains on both sides of the insulating alpha-Fe2O3 boundary. The MR exhibits strong temperature dependence below 100 K and its magnitude is enhanced to reach 1280% at 4.2 K, which may arise from the Coulomb blockade effect.