| 1. |
- Arnalds, Unnar B., 1976-
(författare)
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Magnetic Order in Artificial Structures
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The topic of this thesis is the investigation of the magnetic properties of artificially created magnetic structures. Applying different characterization techniques, ranging from direct imaging methods to reciprocal space techniques, the properties of lithographically patterned arrays of magnetic thin film and multilayer elements are investigated by exploring their magnetic state, extending from the atomic scale up to collective ordering phenomena of nano-magnetic elements.Laterally patterned amorphous multilayer arrays of combined circular and ellipsoidal islands were investigated. The arrays contain a variety of length scales, ranging from their nanometer scale multilayer structure to their lateral periodicity in the micrometer range. The attributes of these arrays are explored using different techniques, applicable for addressing the magnetization at different length scales, including magneto-optical techniques, micromagnetic simulations and x-ray resonant magnetic scattering.Arrays of dipole interacting elongated magnetic elements composed of Pd(Fe) thin films were investigated. Pd(Fe) films have a low Curie temperature which can be tuned by the thickness of the Fe layer embedded in Pd. By this, the interaction and the shape anisotropy energies can be brought down to energy scales comparable to room temperature enabling the possibility of investigating the effect of thermal excitations on such arrays. The temperature dependent magnetization of an artificial square spin ice array was investigated by magneto-optical measurements demonstrating the possibility of observing an order-disorder transition in an artificial square spin ice system. The role of dipolar interactions and the possibility of achieving thermal ground state ordering was then further investigated by magnetically sensitive photoemission electron microscopy imaging of ring arrangements of elongated Pd(Fe) elements. The results reveal a high probability of achieving a thermal ground state ordering of the magnetization of the islands.
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| 2. |
- Arnalds, Unnar B., et al.
(författare)
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Thermal transitions in nano-patterned XY-magnets
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:4, s. 042409-
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated ultra-thin disc shaped islands wherein shape anisotropy confines the moment to the island plane, creating XY-like superspins. At low temperatures, the superspins are blocked, and, as the temperature is increased, they undergo a transition into a superparamagnetic state. The onset of this dynamic superspin state scales with the diameter of the islands, and it persists up to a temperature governed by the intrinsic ordering temperature of the island material defining a range in temperature in which dynamic behavior of the magnetic islands can be obtained.
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| 3. |
- Magnus, Fridrik, et al.
(författare)
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Current-voltage-time characteristics of the reactive Ar/N2 high power impulse magnetron sputtering discharge
- 2011
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 110:8
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Tidskriftsartikel (refereegranskat)abstract
- The discharge current and voltage waveforms have been measured in a reactive high power impulse magnetron sputtering (HiPIMS) Ar/N2" role="presentation">N2 discharge with a Ti target for 400 μs" role="presentation">μs long pulses. We observe that the current waveform in the reactive Ar/N2" role="presentation">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.
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| 4. |
- Magnus, Fridrik, et al.
(författare)
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Current-voltage-time characteristics of the reactive Ar/O2 high power impulse magnetron sputtering discharge
- 2012
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 30:5
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Magnus, Fridrik, et al.
(författare)
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Nucleation and resistivity of ultrathin TiN films grown by high power impulse magnetron sputtering
- 2012
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Ingår i: IEEE Electron Device Letters. - : IEEE. - 0741-3106 .- 1558-0563. ; 33:7, s. 1045-1047
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Tidskriftsartikel (refereegranskat)abstract
- TiN films have been grown on SiO 2 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 SiO 2 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.
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| 6. |
- Mockuté, Aurelija, et al.
(författare)
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Synthesis and characterization of arc deposited magnetic (Cr,Mn)(2)AlC MAX phase films
- 2014
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Ingår i: Physica Status Solidi. Rapid Research Letters. - : Wiley. - 1862-6254 .- 1862-6270. ; 8:5, s. 420-423
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Tidskriftsartikel (refereegranskat)abstract
- (Cr1-xMnx)(2)AlC MAX phase thin films were synthesized by cathodic arc deposition. Scanning transmission electron microscopy including local energy dispersive X-ray spectroscopy analysis of the as-deposited films reveals a Mn incorporation of as much as 10 at% in the structure, corresponding to x = 0.2. Magnetic properties were characterized with vibrating sample magnetometry, revealing a magnetic response up to at least room temperature. We thus verify previous theoretical predictions of an antiferromagnetic or ferromagnetic ground state for Cr2AlC upon alloying with Mn. ((c) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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| 7. |
- Pálsson, Gunnar K., et al.
(författare)
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Proximity effects on the H absorption in ultra-thin V layers
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:4, s. 045420-
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Tidskriftsartikel (refereegranskat)abstract
- We discuss proximity effects on the hydrogen uptake in 14 atomic layers of vanadium. The enthalpy and entropy of solution were measured and compared to ab initio density functional calculations. We show that there exists a large difference in the hydrogen uptake of V in Cr/V and Fe/V superlattices, in which the V is under close to identical strain states. The calculations show that neither local strain effects nor charge redistributions can be the cause for the observed effect. This leaves magnetic and long ranged elastic strain fields-neither captured by the current calculations-as possible mechanisms for the observed effects.
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