Publications of Thomas Ostler     Results 1-20 of 34. 1 2   A multiscale model of the effect of Ir thickness on the static and dynamic properties of Fe/Ir/Fe filmsCuadrado, Ramón; Oroszlány, László; Szunyogh, László et alin Scientific Reports (2018), 8Detailed reference viewed: 9 (1 ULiège) Conditions for thermally induced all-optical switching in ferrimagnetic alloys: Modeling of TbCoMoreno, Roberto; Ostler, Thomas ; Chantrell, Roy et alin Physical Review B (2017), 96Detailed reference viewed: 15 (2 ULiège) Substrate Induced Strain Field in FeRh Epilayers Grown on Single Crystal MgO (001) SubstratesBarton, C. W.; Ostler, Thomas ; Huskisson, D. et alin Scientific Reports (2017), 7Equi-atomic FeRh is highly unusual in that it undergoes a rst order meta-magnetic phase transition from an antiferromagnet to a ferromagnet above room temperature (Tr ≈ 370 K). This behavior opens new ... [more ▼]Equi-atomic FeRh is highly unusual in that it undergoes a rst order meta-magnetic phase transition from an antiferromagnet to a ferromagnet above room temperature (Tr ≈ 370 K). This behavior opens new possibilities for creating multifunctional magnetic and spintronic devices which can utilise both thermal and applied eld energy to change state and functionalise composites. A key requirement in realising multifunctional devices is the need to understand and control the properties of FeRh in the extreme thin lm limit (tFeRh < 10 nm) where interfaces are crucial. Here we determine the properties of FeRh lms in the thickness range 2.5–10 nm grown directly on MgO substrates. Our magnetometry and structural measurements show that a perpendicular strain eld exists in these thin films which results in an increase in the phase transition temperature as thickness is reduced. Modelling using a spin dynamics approach supports the experimental observations demonstrating the critical role of the atomic layers close to the MgO interface. [less ▲]Detailed reference viewed: 27 (3 ULiège) Modeling the thickness dependence of the magnetic phase transition temperature in thin FeRh filmOstler, Thomas ; Craig, Barton; Thomas, Thomson et alin Physical Review. B : Condensed Matter (2017), 95FeRh and its first-order phase transition can open new routes for magnetic hybrid materials and devices under the assumption that it can be exploited in ultra-thin-film structures. Motivated by ... [more ▼]FeRh and its first-order phase transition can open new routes for magnetic hybrid materials and devices under the assumption that it can be exploited in ultra-thin-film structures. Motivated by experimental measurements showing an unexpected increase in the phase transition temperature with decreasing thickness of FeRh on top of MgO, we develop a computational model to investigate strain effects of FeRh in such magnetic structures. Our theoretical results show that the presence of theMgO interface results in a strain that changes the magnetic configuration which drives the anomalous behavior. [less ▲]Detailed reference viewed: 33 (1 ULiège) Towards Optimization of Thermally Induced Magnetization SwitchingOstler, Thomas Conference (2016, November 04)Detailed reference viewed: 23 (2 ULiège) First Order Phase Transition in FePt/FeRh BilayersOstler, Thomas ; Barton, Craig; Hrkac, Gino et alConference (2016, November 01)Detailed reference viewed: 35 (1 ULiège) Effects of interactions on the relaxation processes in magnetic nanostructuresAtkinson, Lewis; Ostler, Thomas ; Ondrej, Hovorka et alin Physical Review. B: Condensed Matter and Materials Physics (2016), 94Controlling the relaxation of magnetization in magnetic nanostructures is key to optimizing magnetic storage device performance. This relaxation is governed by both intrinsic and extrinsic relaxation ... [more ▼]Controlling the relaxation of magnetization in magnetic nanostructures is key to optimizing magnetic storage device performance. This relaxation is governed by both intrinsic and extrinsic relaxation mechanisms and with the latter strongly dependent on the interactions between the nanostructures. In the present work we investigate laser induced magnetization dynamics in a broadband optical resonance type experiment revealing the role of interactions between nanostructures on the relaxation processes of granular magnetic structures. The results are corroborated by constructing a temperature dependent numerical micromagnetic model of magnetization dynamics based on the Landau-Lifshitz-Bloch equation. The model predicts a strong dependence of damping on the key material properties of coupled granular nanostructures in good agreement with the experimental data. We show that the intergranular, magnetostatic and exchange interactions provide a large extrinsic contribution to the damping. Finally we show that the mechanism can be attributed to an increase in spin-wave degeneracy with the ferromagnetic resonance mode as revealed by semianalytical spin-wave calculations. [less ▲]Detailed reference viewed: 19 (3 ULiège) Competition of phonon and magnon effects in the temperature dependence of spinwave stiffnessOstler, Thomas ; Verstraete, Matthieu ; Di Gennaro, Marco et alConference (2016, September 21)Magnons are the elementary magnetic excitations in ordered solids. Understanding such collective excitations is important for a number of technologically relevant fields, such as, magnonics [1] or spin ... [more ▼]Magnons are the elementary magnetic excitations in ordered solids. Understanding such collective excitations is important for a number of technologically relevant fields, such as, magnonics [1] or spin caloritronics [2]. The central interactions in spin caloritronics are the couplings of phonons with electrons and spin degrees of freedom. Furthermore, understanding the effects of temperature on the phonon and spin degrees of freedom adds a further complexity. In the present work we have developed a multiscale model of ferromagnetic materials and demonstrate the effect of temperature dependent phonon displacements on the magnons spectra. Our results show that the for Fe and Ni the effect of phonon displacements acts to reduce the Curie temperature, whereas for Permalloy the opposite is true due to an increased long-ranged exchange interaction. This increased exchange interaction results in an increasing spin-wave stiffness with increasing temperature, overcoming the usual decrease due to magnon softening. To determine the effects of increasing the phonon temperature we have developed a multiscale model whereby we begin by calculating the thermal displacement of phonons, $\sqrt{\langle u^2(T) \rangle}$, calculated using the phonopy software package [3] using electronic ground state and phonon properties determined using the ABINIT software package [4]. Then the exchange constants are determined using the SPRKKR package [5]. Finally, we use linear spin wave theory to determine the effect of the phonon temperature on the exchange alone, demonstrating an increasing frequency of the acoustic magnon branch. We take into account the thermal effects of the magnetic system through the use of the atomistic spin dynamics approach. Magnon softening due to thermal effects demonstrates a more modest increase in the exchange stiffness (over the purely phononic effect), however, an overall increase is still observed. \newline \newline [1] A. V. Chumak, V. I. Vasyuchka, A. A. Serga, and B. Hillebrands, Nature Physics, {\bf 11}, 453–461 (2015). \newline [2] G. E. W. Bauer, E. Saitoh, and B. J. van Wees, Nature Materials {\bf 11}, 391 (2012). \newline [3] Atsushi Togo and Isao Tanaka, Scr. Mater., {\bf 108}, 1-5 (2015) \newline [4] X. Gonze \textit{et al.} Computer Physics Communications {\bf 180}, 2582-2615 (2009). \newline [5] T. Huhne \textit{at al.} Physical Review B, {\bf 58}, 10236 (1998). [less ▲]Detailed reference viewed: 244 (3 ULiège) Ultrafast Spin Dynamics in FeRhOstler, Thomas Conference (2016, July 16)Detailed reference viewed: 24 (1 ULiège) Towards optimization of thermally induced magnetization swithcing in alloys and structured materialsOstler, Thomas Conference (2016, June 28)Detailed reference viewed: 7 (1 ULiège) Strain induced vortex core switching in planar magnetostrictive nanostructuresOstler, Thomas Conference (2016, June 26)Detailed reference viewed: 5 (1 ULiège) Thermally induced magnetization switching in Gd/Fe multilayersXu, Chudong; Ostler, Thomas ; Chantrell, Royin Physical Review B (2016), 93A theoretical model of Gd/Fe multilayers is constructed using the atomistic spin dynamics formalism. By varying the thicknesses and number of layers we have shown that a strong dependence of the energy ... [more ▼]A theoretical model of Gd/Fe multilayers is constructed using the atomistic spin dynamics formalism. By varying the thicknesses and number of layers we have shown that a strong dependence of the energy required for thermally induced magnetization switching (TIMS) is present;with a larger number of interfaces, lower energy is required. The results of the layer resolved dynamics show that the reversal process of the multilayered structures, similar to that of a GdFeCo alloy, is driven by the antiferromagnetic interaction between the transition-metal and rare-earth components. Finally, while the presence of the interface drives the reversal process, we show here that the switching process does not initiate at the surface but from the layers furthest from it, a departure from the alloy behavior which expands the classes of material types exhibiting TIMS. [less ▲]Detailed reference viewed: 12 (1 ULiège) Optimal electron, phonon, and magnetic characteristics for low energy thermally induced magnetization switchingAtxitia, U.; Ostler, Thomas ; Chantrell, R. W. et alin Applied Physics Letters (2015), 107(19), 192402Using large-scale computer simulations, we thoroughly study the minimum energy required to ther- mally induced magnetization switching (TIMS) after the application of a femtosecond heat pulse in ... [more ▼]Using large-scale computer simulations, we thoroughly study the minimum energy required to ther- mally induced magnetization switching (TIMS) after the application of a femtosecond heat pulse in transition metal-rare earth ferrimagnetic alloys. We find that for an energy efficient TIMS, a low ferrimagnetic net magnetization with a strong temperature dependence is the relevant factor for the magnetic system. For the lattice and electron systems, the key physics for efficient TIMS is a large electron-phonon relaxation time. Importantly, we show that as the cooling time of the heated elec- trons is increased, the minimum power required to produce TIMS can be reduced by an order of magnitude. Our results show the way to low power TIMS by appropriate engineering of magnetic heterostructures. [less ▲]Detailed reference viewed: 16 (1 ULiège) Magnon excitations in atomistic spin dynamics due to spin-lattice couplingOstler, Thomas ; Ellis, Matthew; Chantrell, RoyConference (2015, October 22)Detailed reference viewed: 28 (2 ULiège) Ultrafast Magnetism at Complex InterfacesOstler, Thomas Conference (2015, October 21)Detailed reference viewed: 21 (1 ULiège) Thermally Induced Magnetization Switching in Gd/Fe MultilayersOstler, Thomas ; Xu, Chudong; Chantrell, RoyConference (2015, October 20)Detailed reference viewed: 10 (1 ULiège) Ultrafast and Distinct Spin Dynamics in Magnetic AlloysRadu, I.; Stamm, C.; Eschenlohr, A. et alin Spin (2015), 5(3), 1550004Detailed reference viewed: 14 (2 ULiège) Strain Induced Vortex Core Switching in Planar Magnetostrictive NanostructuresOstler, Thomas ; Cuadrado, R.; Chantrell, R. W. et alin Physical review letters (2015), 115(6), 067202Detailed reference viewed: 11 (2 ULiège) The Landau–Lifshitz equation in atomistic modelsEllis, M. O. A.; Evans, R. F. L.; Ostler, Thomas et alin Low Temperature Physics (2015), 41(9), 705-712Detailed reference viewed: 5 (0 ULiège) Engineering Ultrafast MagnetismRadu, I.; Stamm, C.; Eschenlohr, A. et alin Ultrafast Magnetism I (2015)Detailed reference viewed: 9 (0 ULiège) 1 2