| 1. |
- Dahlqvist, Martin, et al.
(författare)
-
Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC
- 2016
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 93:1
-
Tidskriftsartikel (refereegranskat)abstract
- Inherently layered magnetic materials, such as magnetic M(n+1)AX(n) (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M(n+1)AX(n) consists of M(n+1)AX(n) blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn2GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn2GaC MAX phases in future magnetoelectric and magnetocaloric applications.
|
|
| 2. |
- Frisk, Andreas, 1983-, et al.
(författare)
-
Tailoring anisotropy and domain structure in amorphous TbCo thin films through combinatorial methods
- 2016
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 49:3
-
Tidskriftsartikel (refereegranskat)abstract
- We apply an in-plane external magnetic field during growth of amorphous TbCo thin films and examine the effects on the magnetic anisotropy and domain structure. A combinatorial approach is employed throughout the deposition and analysis to study a continuous range of compositions between 7–95 at.% Tb. Magnetometry measurements show that all samples have a strong out-of-plane anisotropy, much larger than any in-plane components, regardless of the presence of a growth field. However, magnetic force microscopy demonstrates that the growth field does indeed have a large effect on the magnetic domain structure, resulting in elongated domains aligned along the imprinting field direction. The results show that the anisotropy can be tuned in intricate ways in amorphous TbCo films giving rise to unusual domain structures. Furthermore the results reveal that a combinatorial approach is highly effective for mapping out these material properties.
|
|
| 3. |
- Magnus, Fridrik, et al.
(författare)
-
Long-range magnetic interactions and proximity effects in an amorphous exchange-spring magnet
- 2016
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality.
|
|
| 4. |
- Magnus, Fridrik, et al.
(författare)
-
Sequential magnetic switching in Fe/MgO(001) superlattices
- 2018
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 97:17
-
Tidskriftsartikel (refereegranskat)abstract
- Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchangecoupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90◦periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the toplayer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180◦periodic alignment isobtained at remanence and with increasing applied field the layer switching starts from the two outermost layersand proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensionalmagnetic structures with a predefined discrete switching sequence
|
|
| 5. |
- Meshkian, Rahele, et al.
(författare)
-
A magnetic atomic laminate from thin film synthesis: (Mo0.5Mn0.5)2GaC
- 2015
-
Ingår i: APL Materials. - : American Institute of Physics (AIP): Open Access Journals / AIP Publishing LLC. - 2166-532X. ; 3:7
-
Tidskriftsartikel (refereegranskat)abstract
- We present synthesis and characterization of a new magnetic atomic laminate: (Mo0.5Mn0.5)(2)GaC. High quality crystalline films were synthesized on MgO(111) substrates at a temperature of similar to 530 degrees 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 mu(B) 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.
|
|
| 6. |
- Meshkian, Rahele, et al.
(författare)
-
Theoretical stability, thin film synthesis and transport properties of the Mon+1GaCn MAX phase
- 2015
-
Ingår i: Physica Status Solidi. Rapid Research Letters. - : Wiley. - 1862-6254 .- 1862-6270. ; 9:3, s. 197-201
-
Tidskriftsartikel (refereegranskat)abstract
- The phase stability of Mon +1GaCn has been investigated using ab-initio calculations. The results indicate stability for the Mo2GaC phase only, with a formation enthalpy of 0.4 meV per atom. Subsequent thin film synthesis of Mo2GaC was performed through magnetron sputtering from elemental targets onto Al2O3 [0001], 6H-SiC [0001] and MgO [111] substrates within the temperature range of 500 degrees C and 750 degrees C. High structural quality films were obtained for synthesis on MgO [111] substrates at 590 degrees C. Evaluation of transport properties showed a superconducting behavior with a critical temperature of approximately 7 K, reducing upon the application of an external magnetic field. The results point towards the first superconducting MAX phase in thin film form.
|
|
| 7. |
- Moubah, Reda, et al.
(författare)
-
Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
- 2016
-
Ingår i: Physical Review Applied. - : American physical society. - 2331-7019. ; 5:4
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.
|
|
| 8. |
- Novoselova, Iuliia P., et al.
(författare)
-
Large uniaxial magnetostriction with sign inversion at the first order phase transition in the nanolaminated Mn2GaC MAX phase
- 2018
-
Ingår i: Scientific Reports. - London : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- In 2013, a new class of inherently nanolaminated magnetic materials, the so called magnetic MAX phases, was discovered. Following predictive material stability calculations, the hexagonal Mn2GaC compound was synthesized as hetero-epitaxial films containing Mn as the exclusive M-element. Recent theoretical and experimental studies suggested a high magnetic ordering temperature and non-collinear antiferromagnetic (AFM) spin states as a result of competitive ferromagnetic and antiferromagnetic exchange interactions. In order to assess the potential for practical applications of Mn2GaC, we have studied the temperature-dependent magnetization, and the magnetoresistive, magnetostrictive as well as magnetocaloric properties of the compound. The material exhibits two magnetic phase transitions. The Neel temperature is T-N similar to 507 K, at which the system changes from a collinear AFM state to the paramagnetic state. At T-t = 214 K the material undergoes a first order magnetic phase transition from AFM at higher temperature to a non-collinear AFM spin structure. Both states show large uniaxial c-axis magnetostriction of 450 ppm. Remarkably, the magnetostriction changes sign, being compressive (negative) above T-t and tensile (positive) below the T-t. The sign change of the magnetostriction is accompanied by a sign change in the magnetoresistance indicating a coupling among the spin, lattice and electrical transport properties.
|
|
| 9. |
- Petruhins, Andrejs, et al.
(författare)
-
Synthesis and characterization of magnetic (Cr0.5Mn0.5)2GaC thin films
- 2015
-
Ingår i: Journal of Materials Science. - : Springer Berlin/Heidelberg. - 0022-2461 .- 1573-4803. ; 50:13, s. 4495-4502
-
Tidskriftsartikel (refereegranskat)abstract
- Growth of (Cr0.5Mn0.5)2GaC thin films from C, Ga, and compound Cr0.5Mn0.5 targets is reported for depositions on MgO (111), 4H-SiC (0001), and Al2O3 (0001) with and without a NbN (111) seed layer. Structural quality is found to be highly dependent on the choice of substrate with MgO (111) giving the best results as confirmed by X-ray diffraction and transmission electron microscopy. Phase pure, high crystal quality MAX phase thin films are realized, with a Cr:Mn ratio of 1:1. Vibrating sample magnetometry shows a ferromagnetic component from 30 K up to 300 K, with a measured net magnetic moment of 0.67 μB per metal (Cr + Mn) atom at 30 K and 5 T. The temperature dependence of the magnetic response suggests competing magnetic interactions with a resulting non-collinear magnetic ordering.
|
|
| 10. |
- Procter, R. A., et al.
(författare)
-
Magnetic leverage effects in amorphous SmCo/CoAlZr heterostructures
- 2015
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:6
-
Tidskriftsartikel (refereegranskat)abstract
- Although magnetic heterostructures are the basis of many magnetic technologies, the mechanisms involved in magnetization reversals in such structures are not fully understood, especially in amorphous multilayers. Here, we report on the SmCo/CoAlZr system and exploit resonant magnetic x-ray scattering to probe the element specific magnetization reversals. When combined into a tri-layer structure, two different switching fields and reversal mechanisms are observed for the Sm and Co sub-lattices. We argue that the decoupling of the sub-lattices arises from the local distribution of atomic species within the amorphous matrix leading to a strong magnetic leverage effect and exchange pinning. The decoupling arises due to strong interactions between regions of high Co density which span the interface. The relatively sparse interactions between Sm and Co induce a localized pinning of the Co-rich areas, resulting in an exchange bias in minor loops and an enhanced coercivity.
|
|
