The preparation and definition of large (3 - 5 mm edge length) single crystals of ScN, GdN, TbN, HoN, YbN and CeN is described. The Hall effect and the electrical conductivity are found to be metallic. The optical ref...The preparation and definition of large (3 - 5 mm edge length) single crystals of ScN, GdN, TbN, HoN, YbN and CeN is described. The Hall effect and the electrical conductivity are found to be metallic. The optical reflectivity between 30 meV (sometimes 1 meV) and 13 eV has been measured and the dielectric functions have been obtained. A plasma edge in the infrared confirms the metallic character. In GdN, a shift of this plasma edge with temperature through the magnetic ordering temperature has been observed as a new effect. GdN is in low magnetic fields antiferromagnetic, but becomes ferromagnetic in larger fields. The band structure is discussed. The magnetic exchange interactions have been derived. HoN in the relevant crystal directions has a spontaneous magnetic moment, but no saturation in fields up to 10 T. CeN is intermediate valent and exhibits a Pauli paramagnetism. The specific heat is measured down to 0.3 K and an enhanced?γ value is observed.展开更多
Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for a...Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for applied magnetic fields of only 10 Oe, become ferromagnetic for excess electrons and larger magnetic fields. They are semimetallic. Thin films are ferromagnetic and semiconductors. Over the time, many experiments have been performed on both systems and the physics in each system is consistent. Band structure computations either yield ferromagnetic semimetals or ferromagnetic semiconducting thin films. There seems to be two incompatible worlds, those of single crystals and those of thin films. In the present work, the author compares directly the various measurements and calculations and gives reasons for their different results.展开更多
文摘The preparation and definition of large (3 - 5 mm edge length) single crystals of ScN, GdN, TbN, HoN, YbN and CeN is described. The Hall effect and the electrical conductivity are found to be metallic. The optical reflectivity between 30 meV (sometimes 1 meV) and 13 eV has been measured and the dielectric functions have been obtained. A plasma edge in the infrared confirms the metallic character. In GdN, a shift of this plasma edge with temperature through the magnetic ordering temperature has been observed as a new effect. GdN is in low magnetic fields antiferromagnetic, but becomes ferromagnetic in larger fields. The band structure is discussed. The magnetic exchange interactions have been derived. HoN in the relevant crystal directions has a spontaneous magnetic moment, but no saturation in fields up to 10 T. CeN is intermediate valent and exhibits a Pauli paramagnetism. The specific heat is measured down to 0.3 K and an enhanced?γ value is observed.
文摘Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for applied magnetic fields of only 10 Oe, become ferromagnetic for excess electrons and larger magnetic fields. They are semimetallic. Thin films are ferromagnetic and semiconductors. Over the time, many experiments have been performed on both systems and the physics in each system is consistent. Band structure computations either yield ferromagnetic semimetals or ferromagnetic semiconducting thin films. There seems to be two incompatible worlds, those of single crystals and those of thin films. In the present work, the author compares directly the various measurements and calculations and gives reasons for their different results.
