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Chromium dioxide (CrO2) films have been grown epitaxially on (100) TiO2 substrates using chemical vapor deposition and their magnetic properties were studied as a function of film thickness (500 A–1.2 μm). Because of the lattice mismatch with the substrate, the films are strained as evidenced by x-ray diffraction measurements. The amount of strain depends on the thickness and also on the substrate cleaning conditions used prior to growth. Independent of their thickness, the films exhibit a sharp ferromagnetic transition with a Curie temperature in the range of 390–395 K. In-plane magnetic anisotropy is observed for the films, with [001] and [010] being the easy axis and hard axis directions, respectively, for the thicker films. The anisotropy field decreases with decreasing thickness, with the easy and hard axes switching directions for the thinnest films. The results are explained in terms of the competition between magnetocrystalline and strain anisotropies that favor the [001] and [010] magnetization d...

We have studied systematically the magnetotunneling properties of several metallic magnetictunnel-junction systems (Ni80Fe20–insulator–Ni80Fe20,Ni80Fe20–I–Co,Co–I–Co, Ni40Fe60–I–Co). The room-temperature magnetoresistance MR value at zero-bias ranges between 16% and 27%, depending on the spin polarization of the electrodes. There seems to be a general bias dependence of MR in all of these systems. In particular, it requires a bias in the range of 0.22–0.23 V to suppress the maximum MR value by half. We have also measured the bias dependence of MR as a function of barrier parameters (thickness and oxidation time). At low temperature, a sharp cusplike feature appears near zero bias. In some cases, low-temperature MR values substantially exceed expectations from established spin-polarization.

Powder and sintered samples of La0.9MnO3 (LMO) and La0.62Y0.07Ca0.31MnO3 (LYCMO) are used in this study. The two initial calcined in air powders have almost identical ferromagnetic properties with Tc≈250 K, and saturation magnetization of σ≈90 emu/gm corresponding to Mn4+(0.3)/Mn3+(0.7). Heating the calcined powders in argon to high temperatures lowers Tc to ≈120 K; however, subsequent oxygen annealing brings back the high Tc form. The LYCMO remains ferromagnetic with σ≈90 emu/gm in both heat treatments but only has a colossal magnetoresistance (MR) for Tc≈120 K. In contrast the LMO with Tc≈120 K has σ reduced to one-half its ferromagnetic value and the MR is almost zero. Neutron diffraction shows only the ferromagnetic structure below Tc for LYCMO but the low magnetization of LMO is best interpreted as a mixed ferro–antiferromagnetic structure rather than a canted one.

We report the observation of a large magnetoresistance (83%) at low magnetic fields of tens of Oe at 4.2 K in the epitaxial trilayer junction structure, La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. The spin-polarization parameter of the manganite has been determined from the magnetoresistance value. The switching fields of the two magnetic layers were designed by using the magnetic shape anisotropy. By limiting the sweeping field in a low field range (∼100 Oe), we have achieved bistable resistive states at zero field, which is of potential interest for magnetoelectronic applications.

We have fabricated a series of (111)- and (100)-orientated Co/Pt superlattices of high quality. (111)-orientated superlattices acquire a perpendicular magnetic anisotropy for samples with thin Co layers whereas for the (100)-orientated superlattices the easy magnetization direction remains in plane. Analysis of the extraordinary Hall effect (EHE) verifies the applicability of simple scaling laws between the resistivity and the EHE coefficient for these layered materials. In addition, we have found a marked dependence of the skew coefficient on Co layer thickness. The contribution to EHE from quantum side-jump remains relatively constant.

Textured (100) diamond films are successfully grown on single-crystalline (100) silicon substrate by electron assisted hot filament chemical vapor deposition from a gas mixture of methane and hydrogen. The effects of various parameters have been studied. The optimal growth conditions are obtained and the oriental growth character is discussed.

Voltage dependent tunnel magnetoresistance (TMR) has been studied in fully epitaxial (Zn,Co)O∕ZnO∕(Zn,Co)O∕ZnO∕(Zn,Co)O magnetic tunnel junctions (MTJs) with double barrier. The MTJs show extremely small voltage dependence with “half voltage” over 4V above 6K. At 5K, the TMR as a function of voltage is found to be constant up to 2V, and then decreases. “TMR transition” occurs when temperature decreases to 3–4K, and subsequently, the TMR abnormally increases with voltage at 2K. The anomalous voltage dependent TMR is discussed in terms of the large energy separation between the Fermi level and the mobility edge.