Absence of Metal-Insulator-Transition and Coherent Interlayer Transport in oriented graphite in parallel magnetic fields

Measurements of the magnetoresistivity of graphite with a high degree of control of the angle between the sample and magnetic field indicate that the metal-insulator transition (MIT), shown to be induced by a magnetic field applied perpendicular to the layers, does not appear in parallel field orientation. Furthermore, we show that interlayer transport is coherent in less ordered samples and high magnetic fields, whereas appears to be incoherent in less disordered samples. Our results demonstrate the two-dimensionality of the electron system in ideal graphite samples.Comment: 4 figures, details adde

Magnetic Properties of Epitaxial Fe3O4 Films

Epitaxial magnetite thin films with (100), (110) and (111) orientation have been deposited by Laser ablation onto substrates with [NaCl] and [Spinel] structure. X-ray difraction revealed pseudomorphic growth for (100) and (111) oriented films on MgO (100) and ZnFe2O4 (111) respectively, whereas films on MgAl2O4 showed a high degree of relaxation. For films on MgAl2O4 and ZnFe2O4 a significant enhancement of the Verwey-transition temperature compared to bulk material has been observed. The influence of stress on the magnetic anisotropy has been investigated by torque-magnetometry on (110) oriented films. Both films on MgO and spinel show an [110] in plane easy axis, which can be explained by (tensile) stresses in the case of MgO but not in the case of spinel. CEMS pattern indicate out of plane components of the magnetisation for all films. We suggest cation antiphase boundaries, observed by TEM to be responsible for this effect, limiting the magnetic coherence length and thus reducing shape anisotropy