TY - JOUR A1 - Hahn, Marc Benjamin T1 - Temperature in micromagnetism: Cell size and scaling effects of the stochastic Landau-Lifshitz equation JF - Journal of physics communications N2 - The movement of the macroscopic magnetic moment in ferromagnetic systems can be described by the Landau-Lifshitz (LL) or Landau-Lifshitz-Gilbert (LLG) equation. These equations are strictly valid only at absolute zero temperature. To include temperature effects a stochastic version of the LL or LLG equation for a spin density of one per unit cell can be used instead. To apply the stochastic LL to micromagnetic simulations, where the spin density per unit cell is generally higher, a conversion regarding simulation cell size and temperature has to be established. Based on energetic considerations, a conversion for ferromagnetic bulk and thin film systems is proposed. The conversion is tested in micromagnetic simulations which are performed with the Object Oriented Micromagnetic Framework (OOMMF). The Curie temperatures of bulk Nickel, Cobalt and Iron systems as well as Nickel thin-film systems with thicknesses between 6.3 mono layer (ML) and 31ML are determined from micromagnetic simulations. The results show a good agreement with experimentally determined Curie temperatures of bulk and thin film systems when temperature scaling is performed according to the presented model. KW - Micromagnetism KW - LLG KW - LL equation KW - Landau Lifshitz equation KW - Landau Lifshitz Gilbert equation KW - Stochastic Landau Lifshitz equation KW - Stochastic Landau Lifshitz Gilbert equation KW - Curie temperature KW - Magnetic Nanoparticles KW - Thin film systems KW - Temeprature scaling KW - Phase transition KW - Magnet coupling KW - Ferromagnetism KW - Superparamagnetism KW - Paramagnetism KW - Ni KW - Co KW - Fe KW - Steel KW - Nickel KW - Cobalt KW - Iron KW - Temperature effects KW - Cell size KW - Damping factor KW - Gamma KW - Alpha KW - Spin KW - Magnetic moment KW - Magnetic interacion KW - Magnetization dynamics KW - Domain wall KW - Exchange length KW - temeprature dependent exchange length KW - Bloch wall KW - Neel wall KW - Exchange interaction KW - Magnetic anisotropy KW - Simulation KW - OOMMF KW - Object oriented micromagnetic framework PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-484610 DO - https://doi.org/10.1088/2399-6528/ab31e6 VL - 3 IS - 7 SP - 075009-1 EP - 075009-8 PB - IOPscience CY - England AN - OPUS4-48461 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Akbar, S. A1 - Hasanain, S.K. A1 - Ivashenko, O. A1 - Dutka, M.V. A1 - Akhtar, N. A1 - De Hosson, J.Th.M. A1 - Ali, Naveed A1 - Rudolf, P. T1 - Defect ferromagnetism in SnO2:Zn2+ hierarchical nanostructures: correlation between structural, electronic and magnetic properties JF - RSC Advances N2 - We report on the ferromagnetism of Sn1-xZnxO2 (x < 0.1) hierarchical nanostructures with various morphologies synthesized by a solvothermal route. A room temperature ferromagnetic and paramagnetic response was observed for all compositions, with a maximum in ferromagnetism for x = 0.04. The ferromagnetic behaviour was found to correlate with the presence of zinc on substitutional Sn sites and with a low oxygen vacancy concentration in the samples. The morphology of the nanostructures varied with zinc concentration. The strongest ferromagnetic response was observed in nanostructures with well-formed shapes, having nanoneedles on their surfaces. These nanoneedles consist of (110) and (101) planes, which are understood to be important in stabilizing the ferromagnetic defects. At higher zinc concentration the nanostructures become eroded and agglomerated, a phenomenon accompanied with a strong decrease in their ferromagnetic response. The observed trends are explained in the light of recent computational studies that discuss the relative stability of ferromagnetic defects on various surfaces and the role of oxygen vacancies in degrading ferromagnetism via an increase in free electron concentration. KW - Ferromagnetism KW - Nanostructures KW - Magnetic properties PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-473014 DO - https://doi.org/10.1039/c9ra00455f SN - 2046-2069 VL - 9 IS - 7 SP - 4082 EP - 4091 PB - Royal Society of Chemistry AN - OPUS4-47301 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -