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| 2. |
- Löfstrand, Julia, et al.
(författare)
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Tuning in-plane magnetic anisotropy and temperature stability in amorphous trilayers
- 2023
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 586
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Tidskriftsartikel (refereegranskat)abstract
- Better understanding of the nature of magnetic coupling in soft/hard nanocomposites paves the way for tailored exchange-spring magnets. We have investigated a series of amorphous magnetic thin films and trilayers of magnetically soft Co85(Al70Zr30)15 and magnetically hard Sm12Co81Ti7, produced with DC magnetron sputtering. The overall magnetic properties of the trilayers were investigated with focus on the effects of layer configuration and thicknesses on coercivity, originating from the Sm12Co81Ti7 phase, and uniaxial in-plane anisotropy induced from the Co85(Al70Zr30)15 phase. In addition, we found that the thermal stability of a 20 nm Sm12Co81Ti7 layer was significantly increased if surrounded by two 10 nm Co85(Al70Zr30)15 layers in a trilayer structure.
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| 3. |
- Mottamchetty, Venkatesh, et al.
(författare)
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Direct evidence of terahertz emission arising from anomalous Hall effect
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- A detailed understanding of the different mechanisms being responsible for terahertz (THz) emission in ferromagnetic (FM) materials will aid in designing efficient THz emitters. In this report, we present direct evidence of THz emission from single layer Co0.4Fe0.4B0.2 (CoFeB) FM thin films. The dominant mechanism being responsible for the THz emission is the anomalous Hall effect (AHE), which is an effect of a net backflow current in the FM layer created by the spin polarized current reflected at the interfaces of the FM layer. The THz emission from the AHE-based CoFeB emitter is optimized by varying its thickness, orientation, and pump fluence of the laser beam. Results from electrical transport measurements show that skew scattering of charge carriers is responsible for the THz emission in the CoFeB AHE-based THz emitter.
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| 4. |
- Rani, Parul
(författare)
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Magnetic properties of hard-soft amorphous nanolaminates
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Amorphous magnetic thin film heterostructures and multilayers are often used in data storage as well as spintronic devices. Spintronics will help the next generation of nano-electronic devices to increase their memory and processing power and reduce their power consumption. This thesis focuses on the developments of hard and soft amorphous thin films as well as soft/hard multilayers, with an emphasis on the optimization of these materials for use in, for example, spintronics applications. The key for optimization lies in the understanding of the fundamental relationships between structural disorder, composition, and macroscopic magnetic properties.The first part of thesis presents a systematic combinatorial study of composition-structure-property relationships in amorphous alloy thin films of SmCoTi and CoZr, with a particular emphasis on tuning the coercivity µ0Hc ordering temperature Tc, and saturation magnetization Ms with composition. It has been found that 5-7 at.% Ti increases the room temperature coercivity approximately by a factor of ~ 2 (maximum µ0Hc ≈ 0.2 T) compared to amorphous SmCo for Co content in the range 80-85 at.%. For CoZr, dilution of Co with Zr decreases the overall Co moment and the ordering temperature. In magnetic multilayered device architectures, these amorphous alloys might be appropriate for use as soft layers (CoZr) or tunable pinning layers (SmCoTi), depending on the application.This thesis also explores the combination of amorphous hard (SmCo or SmCoTi) and soft (CoAlZr) alloys in bilayer, trilayer, and multilayer structures. The sandwiched of hard and soft amorphous layers that are produced by magnetron sputtering exhibit well-defined interfaces without any lattice strain. First-order reversal curve measurements show that the amorphous hard and soft phases are rigidly exchange-coupled, i.e., the soft phase moment always follows the magnetization direction of the hard phase, for up to at least 20 nm thickness. It is easy to imprint uniaxial in-plane anisotropy in these samples. Both the coercivity and the anisotropy constant increase significantly, by a factor of approximately 4, with increased interface density in the case of CoAlZr/SmCoTi multilayers. In soft/hard/soft trilayers with the same materials, thermal stability is enhanced compared to a single hard layer. Experimental results presented in this thesis demonstrate the potential for tuning properties important to applications based on thin films and multilayers.
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| 5. |
- Rani, Parul, et al.
(författare)
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Magnetic Properties versus Interface Density in Rigid-Exchange-Coupled Amorphous Multilayers with Induced Uniaxial Anisotropy
- 2023
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 133:7
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the possibility to tune the saturation magnetization, coercivity, and uniaxial in-plane anisotropy constant in amorphous bilayers and multilayers of Co85(Al70Zr30)15 and Sm11Co82Ti7 through the interface density. From magnetometry and x-ray circular dichroism (XMCD) measurements, we conclude that the easy-axis coercivity ?0?? increases four times when the number of bilayer repetitions, ?, increases from 1 to 10 within a constant total sample thickness of 20 nm. At the same time, the anisotropy constant ?? also increases by a factor four, whereas the saturation magnetization ?? decreases slightly. The Co spin and orbital moments, ?? and ??, are found to be approximately constant within the sample series. The average total Co moment is only 0.8–0.9 ??/atom, but the ??/?? ratio is strongly enhanced compared to pure Co. Magnetization curves extracted from XMCD measurements show that the Co and Sm moments are ferromagnetically coupled for all samples.
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| 6. |
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| 7. |
- Rani, Parul, et al.
(författare)
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Rigid Exchange Coupling in Rare-Earth-Lean Amorphous Hard/Soft Nanocomposites
- 2020
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X. ; 6:11
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Tidskriftsartikel (refereegranskat)abstract
- Electrification of vehicles and renewable energy is increasing the demand for permanent magnets, but the cost and scarcity of rare-earth metals is an obstacle. Creating nanocomposites of rigidly exchange-coupled hard and soft magnets, for which the magnetization reversal occurs as in a single magnetic-phase material, is a promising route toward rare-earth-lean permanent magnets with high energy products. The hard/soft exchange coupling is, however, often reduced due to rough interfaces and structural defects, resulting in exchange-spring behavior rather than rigid exchange coupling. Here, it is shown that artificially sandwiched hard and soft amorphous magnets produced by magnetron sputtering exhibit smooth interfaces, and the first order reversal curve (FORC) technique is used to show that the hard and the soft phases are rigidly exchange coupled. Micromagnetic simulations, using a random-anisotropy model, are used to predict the thickness limit of the rigid exchange coupling. A great advantage of amorphous hard/soft composites is the possibility to obtain a wide range of magnetic properties by finely tuning the composition of the individual phases.
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| 8. |
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| 9. |
- Rani, Parul, et al.
(författare)
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Structural and magnetic properties of amorphous CoxZr100-x films
- 2023
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 108:13
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Tidskriftsartikel (refereegranskat)abstract
- Magnetometry and first-principles density functional theory-based calculations were used to investigate the concentration dependence of magnetic properties of amorphous CoxZr100-x alloys. A linear increase in saturation magnetization (Ms) is observed in both the experiments and calculations. Samples with Co content of at least 62 at.% are inferred to be ferromagnetic at 5 K. The experimentally determined ordering temperature is found to scale quadratically with Co concentration indicating a complex interplay between local structural motifs and magnetic parameters such as exchange interaction and anisotropy.
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| 10. |
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