Fridrik Magnus

A Nanolaminated Magnetic Phase: Mn2GaC

We report on first principles prediction and subsequent synthesis of Mn2GaC, a new member of the inherently nanolaminated Mn+1AXn (MAX) phase family. This phase, the first to include Mn as the sole M element, was synthesized as a heteroepitaxial thin film. The material was theoretically predicted to display magnetic ordering with ferromagnetic (FM) and antiferromagnetic configurations degenerate in energy within the computational accuracy. Vibrating sample magnetometer measurements show FM ordering with a saturation moment of ms=0.29 μB per Mn atom and remanent moment of mr=0.15 μB per Mn atom for temperatures≤230 K.

Current-voltage-time characteristics of the reactive Ar/N2 high power impulse magnetron sputtering discharge

The discharge current and voltage waveforms have been measured in a reactive high power impulse magnetron sputtering (HiPIMS) Ar/N2 discharge with a Ti target for 400 μs long pulses. We observe that the current waveform in the reactive Ar/N2 HiPIMS discharge is highly dependent on the pulse repetition frequency, unlike the non-reactive Ar discharge. The current is found to increase significantly as the frequency is lowered. This is attributed to an increase in the secondary electron emission yield during the self-sputtering phase, when the nitride forms on the target at low frequencies. In addition, self-sputtering runaway occurs at lower discharge voltages when nitrogen is added to the discharge. This illustrates the crucial role of self-sputtering in the behavior of the reactive HiPIMS discharge.

Digital smoothing of the Langmuir probe I-V characteristic

Electrostatic probes or Langmuir probes are the most common diagnostic tools in plasma discharges. The second derivative of the Langmuir probe I-V characteristic is proportional to the electron energy distribution function. Determining the second derivative accurately requires some method of noise suppression. We compare the Savitzky-Golay filter, the Gaussian filter, and polynomial fitting to the Blackman filter for digitally smoothing simulated and measured I-V characteristics. We find that the Blackman filter achieves the most smoothing with minimal distortion for noisy data.

Current–voltage–time characteristics of the reactive Ar/O2 high power impulse magnetron sputtering discharge

The discharge current–voltage–time waveforms are studied in the reactive Ar/O2 high power impulse magnetron sputtering discharge with a titanium target for 400 μs long pulses. The discharge current waveform is highly dependent on both the pulse repetition frequency and discharge voltage and the current increases with decreasing frequency or voltage. The authors attribute this to an increase in the secondary electron emission yield during the self-sputtering phase of the pulse, as an oxide forms on the target.

Comparing resonant photon tunneling via cavity modes and Tamm plasmon polariton modes in metal-coated Bragg mirrors.

Resonant photon tunneling was investigated experimentally in multilayer structures containing a high-contrast (TiO(2)/SiO(2)) Bragg mirror capped with a semitransparent gold film. Transmission via a fundamental cavity resonance was compared with transmission via the Tamm plasmon polariton resonance that appears at the interface between a metal film and a one-dimensional photonic bandgap structure. The Tamm-plasmon-mediated transmission exhibits a smaller dependence on the angle and polarization of the incident light for similar values of peak transmission, resonance wavelength, and finesse. Implications for transparent electrical contacts based on resonant tunneling structures are discussed.

Nucleation and Resistivity of Ultrathin TiN Films Grown by High-Power Impulse Magnetron Sputtering

TiN films have been grown on SiO2 by reactive high-power impulse magnetron sputtering (HiPIMS) at temperatures of 22°C-600°C. The film resistance is monitored in situ to determine the coalescence and continuity thicknesses that decrease with increasing growth temperature with a minimum of 0.38 ± 0.05 nm and 1.7 ± 0.2 nm, respectively, at 400°C. We find that HiPIMS-deposited films have significantly lower resistivity than dc magnetron sputtered (dcMS) films on SiO2 at all growth temperatures due to reduced grain boundary scattering. Thus, ultrathin continuous TiN films with superior electrical characteristics can be obtained with HiPIMS at reduced temperatures compared to dcMS.

A magnetic atomic laminate from thin film synthesis: (Mo0.5Mn0.5)2GaC

We present synthesis and characterization of a new magnetic atomic laminate: (Mo0.5Mn0.5)2GaC. High quality crystalline films were synthesized on MgO(111) substrates at a temperature of ∼530 °C. The films display a magnetic response, evaluated by vibrating sample magnetometry, in a temperature range 3-300 K and in a field up to 5 T. The response ranges from ferromagnetic to paramagnetic with change in temperature, with an acquired 5T-moment and remanent moment at 3 K of 0.66 and 0.35 μB per metal atom (Mo and Mn), respectively. The remanent moment and the coercive field (0.06 T) exceed all values reported to date for the family of magnetic laminates based on so called MAX phases.

Tunable giant magnetic anisotropy in amorphous SmCo thin films

SmCo thin films have been grown by magnetron sputtering at room temperature with a composition of 2–35 at. % Sm. Films with 5 at. % or higher Sm are amorphous and smooth. A giant tunable uniaxial in-plane magnetic anisotropy is induced in the films which peaks in the composition range 11–22 at. % Sm. This cross-over behavior is not due to changes in the atomic moments but rather the local configuration changes. The excellent layer perfection combined with highly tunable magnetic properties make these films important for spintronics applications.

Strain induced changes in magnetization of amorphous Co95Zr5 based multiferroic heterostructures

A clear change in the magnetic anisotropy in a layer of amorphous Co95Zr5 is obtained at the orthorhombic phase transition of the BaTiO3 substrate. The use of an amorphous buffer layer between the ferroelectric substrate and amorphous magnetic film shows that bulk strain governs the change in the magnetic anisotropy of our ferromagnetic-ferroelectric heterostructure. Moreover, we show that the thermal magnetization curves exhibit anisotropic behavior.

Morphology of TiN thin films grown on MgO(001) by reactive dc magnetron sputtering

Thin TiN films were grown by reactive dc magnetron sputtering on single-crystalline MgO(001) substrates at a range of temperatures from room temperature to 600 °C. Structural characterization was carried out using x-ray diffraction and reflection methods. TiN films grow epitaxially on the MgO substrates at growth temperatures of 200 °C and above. The crystal coherence length determined from Laue oscillations and the Scherrer method agrees with x-ray reflection thickness measurements to 6% and within 3% for growth temperatures of 200 and 600 °C, respectively. For lower growth temperatures the films are polycrystalline but highly textured and porous.