Grain boundary magnetism and conductivity in polycrystalline Ti1−xMnxN films by reactive sputtering

Highlights: •The preferred lattice orientation changes from (2 0 0) to (1 1 1) with the increase of x. •The surface morphology evolves from spherical to triangular-pyramid-like islands as x increases. •Weak grain-boundary ferromagnetism with a Curie temperature of higher than 305 K appears. •The films show semiconducting-like behavior with a mechanism of thermal fluctuation-induced tunneling. -- Abstract: Polycrystalline Ti1−xMnxN films with different Mn atomic fractions (x) were grown by reactive facing-target sputtering. The preferred lattice orientation changes from (2 0 0) to (1 1 1) with the increase of x, which makes the surface morphology evolve from spherical to triangular-pyramid-like islands. Weak grain-boundary ferromagnetism with a Curie temperature of higher than 305 K has been observed. The saturation magnetization (Ms) and coercivity do not show a monotonous change with x. Asymmetric M–H curves can be observed at low temperatures, and the shift of M–H curves decreases with the increase of temperature because of the relaxation of the low-temperature pinned moments. All of the films show semiconducting-like behavior with a mechanism of thermal fluctuation-induced tunneling. Magnetoresistance (MR) is negative, but is very small. The small Ms and MR can be ascribed to the weakly ferromagnetic interaction of moments at grain boundaries and low spin polarization