Computational Modelling Group

Dr Ondrej Hovorka

Engineering Sciences (FEE)
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  • ECE Department, Drexel University, Philadelphia PA, USA (PhD, 2007)
  • CIC nanoGUNE Consolider, Donostia-San Sebastián, Spain (Postdoc, 2008-2011)
  • Physics Department, York University, York, UK (Postdoc, 2012-2013)

Research Interests:

  • Statistical mechanics and phase transitions
  • Inverse problems in systems with hysteresis
  • Stochastic processes and complexity

List of Publications:

  1. S. Ruta, O. Hovorka, Pin-Wei Huang, K. Wang, G. Ju, R. Chantrell, “First order reversal curves and intrinsic parameter determination for magnetic materials; limitations of hysteron-based approaches in correlated systems”, Scientific Reports 7, 45218 (2017).

  2. M. Beg, M. Albert, M.-A. Bisotti, D. Cortés-Ortuño, W. Wang, R. Carey, M. Vousden, O. Hovorka, Ch. Ciccarelli, Ch. S. Spencer, Ch. H. Marrows, H. Fangohr, “Dynamics of skyrmionic states in confined helimagnetic nanostructures”, Physical Review B 95, 014433 (2017).

  3. O. Hovorka, “Thermal activation in statistical clusters of magnetic nanoparticles”, Journal of Physics D: Applied Physics 50, 044004 (2017).

  4. L. J. Atkinson, T. A. Ostler, O. Hovorka, K. Wang, B. Lu, G. Ju, J. Hohlfeld, B. Bergman, B. Koopmans, R. W. Chantrell, “Effects of interactions on the relaxation processes in magnetic nanostructures”, Physical Review B 94, 134431 (2016).

  5. R. Carey, M. Beg, M. Albert, M.-A. Bisotti, D. Cortés-Ortuño, M. Vousden, W. Wang, O. Hovorka, H. Fangohr, “Hysteresis of nanocylinders with Dzyaloshinskii-Moriya interaction”, Applied Physics Letters 109, 122401 (2016).

  6. L. Fallarino, O. Hovorka, A. Berger, “Field orientation dependence of magnetization reversal in thin films with perpendicular magnetic anisotropy”, Physical Review B 94, 064408 (2016).

  7. M. Vousden, M. Albert, M. Beg, M.-A. Bisotti, R. Carey, D. Chernyshenko, D. Cortés-Ortuño, W. Wang, O. Hovorka, Ch. H. Marrows, H. Fangohr, “Skyrmions in thin films with easy-plane magnetocrystalline anisotropy”, Applied Physics Letters 108, 132406 (2016).

  8. O. Laslett, S. Ruta, R. W. Chantrell, J. Barker, G. Friedman, O. Hovorka, “Consistent energy barrier distributions in magnetic particle chains”, Physica B 486, 173 (2016).

  9. M. Beg, R. Carey, W. Wang, D. Cortés-Ortuño, M. Vousden, M.-A. Bisotti, M. Albert, D. Chernyshenko, O. Hovorka, R. L. Stamps, H. Fangohr, “Ground state search, hysteretic behaviour, and reversal mechanism of skyrmionic textures in confined helimagnetic nanostructures”, Scientific Reports 5, 17137 (2015).

  10. S. Ruta, R. W. Chantrell, O. Hovorka, “Unified model of hyperthermia via hysteresis heating in systems of interacting magnetic nanoparticles”, Scientific Reports 5, 9090 (2015).

  11. O. Laslett, S. Ruta, J. Barker, R. W. Chantrell, G. Friedman, O. Hovorka, “Interaction effects enhancing magnetic particle detection based on magneto-relaxometry”, Applied Physics Letters 106, 012407 (2015).

  12. T. A. Ostler, J. Barker, R. F L Evans, U. Atxitia, R. W. Chantrell, O. Hovorka, O. Chubykalo-Fesenko, “Multiscale modeling of ultrafast magnetization dynamics”, Ultrafast Magnetism I, Springer Proceedings in Physics 159, 146 (2015).

  13. R. F. L. Evans, Q. Coopman, S. Devos, W. J. Fan, O. Hovorka, R. W. Chantrell, “Atomistic calculation of the thickness and temperature dependence of exchange coupling through a dilute magnetic oxide”, Journal of Physics D: Applied Physics 47, 502001 (2014).

  14. T. Hauet, L. Piraux, S. K. Srivastava, V. A. Antohe, D. Lacour, M. Hehn, F. Montaigne, J. Schwenk, M. A. Marioni, H. J. Hug, O. Hovorka, A. Berger, S. Mangin, F. A. Araujo, “Reversal mechanism, switching field distribution, and dipolar frustrations in Co/Pt bit pattern media based on auto-assembled anodic alumina hexagonal nanobump arrays”, Physical Review B 89, 174421 (2014).

  15. O. Hovorka, J. Baker, G. Friedman, R. Chantrell, “Role of geometrical symmetry in thermally activated processes in clusters of interacting dipolar moments”, Physical Review B 89, 104410 (2014).

  16. A. Pratt, L. Lari, O. Hovorka, A. Shah, Ch. Woffinden, S. P. Tear, Ch. Binns, R. Kroeger, “Enhanced oxidation of nanoparticles through strain-mediated ionic transport”, Nature Materials 13, 26 (2014).

  17. J. Barker, U. Atxitia, T. A. Ostler, O. Hovorka, O. Chubykalo-Fesenko, R. W. Chantrell, “Two-magnon bound state causes ultrafast thermally induced magnetisation switching”, Scientific Reports 3, 3262 (2013).

  18. X. Moya, L. E. Hueso, F. Maccherozzi, A. I. Tovstolytkin, D. I. Podyalovskii, C. Ducati, L. C. Phillips, M. Ghidini, O. Hovorka, A. Berger, M. E. Vickers, E. Defaÿ, S. S. Dhesi, N. D. Mathur, “Giant and reversible extrinsic magnetocaloric effects in La0.7Ca0.3MnO3”, Nature Materials 12, 52 (2013).

  19. R. M. Ferguson, A. P. Khandhar, H. Arami, L. Hua, O. Hovorka, K. M. Krishnan, “Tailoring the magnetic and pharmacokinetic properties of iron oxide magnetic particle imaging tracers”, Biomedizinische Technik / Biomedical Engineering 58, 493 (2013).

  20. O. Hovorka, J. Pressesky, G. Ju, A. Berger, R. W. Chantrell, “Distribution of switching fields in magnetic granular materials”, Applied Physics Letters 101, 182405 (2012).

  21. O. Hovorka, S. Devos, Q. Coopman, W. J. Fan, C. J. Aas, R. F. L. Evans, Xi Chen, G. Ju, R. W. Chantrell, “The Curie temperature distribution of FePt granular magnetic recording media”, Applied Physics Letters 101, 052406 (2012).

  22. A. Rosales-Rivera, N. A. Salazar, O. Hovorka, O. Idigoras, A. Berger, “Determination of critical exponents of inhomogeneous Gd films”, Physica B 407, 3141 (2012).

  23. O. Hovorka, R. F. L. Evans, R. W. Chantrell, Y. Liu, K. A. Dahmen, A. Berger, “Validation of ΔH(M, ΔM)-technique for identification of switching field distributions in the presence of thermal activation”, Journal of Applied Physics 108, 123901 (2010).

  24. F. Burrows, C. Parker, R. F. L. Evans, Y. Hancock, O. Hovorka, R. W. Chantrell, “Energy losses in fine-particle magnetic composites”, Journal of Physics D: Applied Physics 43, 474010 (2010).

  25. O. Hovorka, R. F. L. Evans, R. W. Chantrell, A. Berger, “Rate-dependence of the switching field distribution in nano-scale granular magnetic materials”, Applied Physics Letters 97, 062504 (2010).

  26. O. Hovorka, Yang Liu, Karin A. Dahmen, A. Berger, “On the ability to determine intrinsic switching field distributions from hysteresis loops in the partially correlated magnetization reversal regime”, Journal of Magnetism and Magnetic Materials 322, 459-468 (2010).

  27. O. Hovorka, Yang Liu, Karin A. Dahmen, A. Berger, “Simultaneous determination of inter-granular interactions and intrinsic switching field distributions in magnetic materials”, Applied Physics Letters 95, 192504 (2009).

  28. Y. Liu, O. Hovorka, A. Berger, K. A. Dahmen, “Effects of nonuniform exchange and magnetostatic interactions on the determination of intrinsic switching field distributions”, Journal of Applied Physics 105, 123905 (2009).

  29. A. Berger, O. Hovorka, G. Friedman, E. E. Fullerton, “Non-linear and hysteretic exchange bias”, Physical Review B 78, 224407 (2008).

  30. T. Hauet, C. Günther, O. Hovorka, A. Berger, M.-Y. Im, P. Fisher, O. Hellwig, “Field driven ferromagnetic phase nucleation and propagation in antiferromagnetically coupled multilayer films with perpendicular anisotropy”, Applied Physics Letters 93, 042505 (2008).

  31. O. Hovorka, G. Friedman, “Non-converging hysteresis cycles in random spin networks”, Physical Review Letters 100, 097201 (2008).

  32. O. Hovorka, A. Berger, G. Friedman, “Estimation of exchange coupling distribution on all-ferromagnetic bilayers”, IEEE Transactions on Magnetics 43, 2953 (2007).

  33. O. Hovorka, A. Berger, G. Friedman, “Experimental comparison of exchange bias measurement methodologies”, Journal of Applied Physics 101, 09E515 (2007).

  34. O. Hovorka, A. Berger, G. Friedman, “Center of mass method for exchange bias measurement”, Applied Physics Letters 89, 142531 (2006).

  35. B. B. Yellen, R. M. Erb, D. Halverson, O. Hovorka, G. Friedman “Arraying nonmagnetic colloids by magnetic nanoparticle assemblers”, IEEE Transactions on Magnetics 42, 3548 (2006).

  36. O. Hovorka, A. Berger, G. Friedman, “Preisach model of exchange bias in antiferromagnetically coupled bilayers”, IEEE Transactions on Magnetics 42, 3129 (2006).

  37. O. Hovorka, G. Friedman, “Energy losses in disordered hysteretic systems with dipolar interactions”, Journal of Applied Physics 99, 08D708 (2006).

  38. O. Hovorka, G. Friedman, “Effects of interaction topology, sign, and strength on hysteretic losses”, Physica B 372, 234 (2006).

  39. B. B. Yellen, O. Hovorka, G. Friedman, “Arranging matter by magnetic nanoparticle assemblers”, Proceedings of the National Academy of Sciences of the USA 102, 8860 (2005).

  40. O. Hovorka, G. Friedman, “Closure of minor hysteresis loops in disordered antiferromagnetic systems”, Journal of Applied Physics 97, 10E514 (2005).

  41. O. Hovorka, B. B. Yellen, N. Dan, G. Friedman, “Self-consistent model of field gradient driven particle aggregation in magnetic fluids”, Journal of Applied Physics 97, 10Q306 (2005).

  42. O. Hovorka, G. Friedman, “Onset of reptations and critical hysteretic behavior in disordered systems”, Journal of Magnetism and Magnetic Materials 290-291, 449 (2005).

  43. O. Hovorka, B. B. Yellen, G. Friedman, “Modeling stability of trapped ferromagnetic nanoparticle chains”, IEEE Transactions on Magnetics 39, 2549 (2003).

  44. G. M. Lloyd, V. Singh, M. L. Wang, O. Hovorka, “Temperature compensation and scalability of hysteretic/anhysteretic magnetic-property sensors”, Sensors Journal IEEE 3, 708 (2003).

  45. M. L. Wang, G. M. Lloyd, O. Hovorka, “Development of a remote coil magneto-elastic stress sensor for steel cables”, Proc. SPIE 8th Annual International Symposium on Smart Structures and Materials, Health monitoring and Management of Civil Infrastructure Systems, Newport Beach CA, Vol. 4337, pp. 122 (2001).

Ondrej's team members

Jonathon Waters
Postgraduate Research Student, Engineering Sciences (FEE)
Mark Vousden
Postgraduate Research Student, Engineering Sciences (FEE)

Joint projects with...

Hans Fangohr
Professor, Engineering Sciences (FEE)
Denis Kramer
Lecturer, Engineering Sciences (FEE)