Strain‐Mediated High Conductivity in Ultrathin Antiferromagnetic Metallic Nitrides

Abstract

Strain engineering provides the ability to control the ground states and associated phase transition in the epitaxial films. However, the systematic study of intrinsic characters and their strain dependency in transition-metal nitrides remains challenging due to the difficulty in fabricating the stoichiometric and high-quality films. Here we report the observation of electronic state transition in highly crystalline antiferromagnetic CrN films with strain and reduced dimensionality. Shrinking the film thickness to a critical value of ~ 30 unit cells, a profound conductivity reduction accompanied by unexpected volume expansion is observed in CrN films. The electrical conductivity is observed surprisingly when the CrN layer as thin as single unit cell thick, which is far below the critical thickness of most metallic films. We found that the metallicity of an ultrathin CrN film recovers from an insulating behavior upon the removal of as-grown strain by fabrication of first-ever freestanding nitride films. Both first-principles calculations and linear dichroism measurements reveal that the strain-mediated orbital splitting effectively customizes the relatively small bandgap at the Fermi level, leading to exotic phase transition in CrN. The ability to achieve highly conductive nitride ultrathin films by harness strain-controlling over competing phases can be used for utilizing their exceptional characteristics.

Flexomagnetism and vertically graded Néel temperature of antiferromagnetic Cr2O3 thin films

“…The family of magnetomechanical effects includes piezo- and flexomagnetic responses, which determine the modification of the magnetic order parameter(s) due to homogeneous or inhomogeneous strain, respectively. Piezomagnetic effects are well addressed in literature both for ferro- and antiferromagnetic materials including emergent anisotropy of material parameters when samples are exposed to uniaxial strain 4 , change of material parameters in samples of different thickness 5 , magnetoelasticity 6 , transport effects in homogeneously strained films 7 . Despite the fact that flexomagnetism 8 – 13 is allowed for in the majority of bulk magnetic classes and enforced by boundaries 14 , it is hardly addressed in the literature compared to the case of piezomagnetism 15 – 19 .…”

Advanced Epitaxial Lift‐Off and Transfer Procedure for the Fabrication of High‐Quality Functional Oxide Membranes

“…[31] By exploiting SAO as a sacrificial layer, a wide variety of oxides (and their heterostructures), mostly perovskites, [18,22,25,[32][33][34] but also binary oxides, [30,[35][36][37] have been successively transferred from the parent STO substrate onto other host substrates. Other parent substrates such as LaAlO 3 , [31] Al 2 O 3 , [37] and MgO [38] have also been used as seed crystal for epitaxial growth of SAO.…”

Emergent Magnetic States and Tunable Exchange Bias at 3d Nitride Heterointerfaces

“…Recently, our group reported the fabrication of high-crystalline stoichiometric CrN ultrathin films using the pulsed laser deposition (PLD) technique. [32][33][34][35] The specimens were prepared by laser ablating from a high-pressure synthesized stoichiometric target and compensating the NVs using an in situ atomic nitrogen plasma source. The CrN thin films fabricated in this manner exhibited a paramagnetic-to-antiferromagnetic transition at a temperature close to its bulk value ≈283 K, [36,37] indicating the correct stoichiometry of high-quality CrN films.…”