Boğaziçi Üniversitesi Fizik Seminerleri

Boğaziçi Üniversitesi Fizik Bölümü, Feza Gürsey Seminer Odası

13 Eylül, Salı, 15:30

Thomas Hauet, San Jose Research Center, Hitachi Global Storage Technologies, San Jose CA , USA,
Institut Jean Lamour, Nancy Université, Nancy, France

Controlling switching field and switching field distribution of in assembly of magnetic nanostructures


The origin of switching field distribution (SFD) in large arrays of magnetic nanostructures, i.e. the difference of reversal field from one nanostructure to an other, has recently attracted great interest in the view of developing new generations of high density or high speed memories such as bit patterned media, MRAM or race track memory. Indeed, in these memory designs, bit-to-bit variations in the structural and/or magnetic properties may produce unintended reversal when writing a hard switcher bit or on the contrary allows neighbours to be over-written if these have a lower reversal field [1,2]. More generally, the control of the switching field as independently as possible from the thermal stability is also targeted.

We used [Co/Pd]-based multilayers deposited onto pre-patterned substrates to develop new way to understand and control switching field distribution in nanostructures [3]. Magnetic properties of nanodots arrays up to 1Tb/in2 have been studied. Different SFD origins (dipolar coupling, pre-patterned array quality, and magnetic media growth defects) have been identified and solutions have been proposed for lowering them [3,4]. We will particularly focus on new exchange coupled composite structures (so-called ECC media) that allow tuning both reversal field and SFD [4,5]. The gain in switching field distribution offered by ECC media originates from introducing incoherency into the magnetization reversal process, which will be discussed on the basis of micromagnetic simulation multi-spin generalization of the macro-spin potential surface model developed by Bertram and Lengsfield [6].

[1] M.E. Schabes, J. Magn. Mag. Mat. 320, 2880 (2008)

[2] O. Ozatay, T. Hauet et al., Chapter “Spin-based data storage”, p236, chapter 7, “Handbook of nanoscale optics and electronics” Elsevier B.V. (2009).

[3] O. Hellwig, T. Hauet et al., Appl. Phys. Lett. 95, 232505 (2009)

[4] T. Hauet et al., Appl. Phys. Lett. 95, 262504 (2009)

[5] T. Hauet et al., Appl. Phys. Lett. 95, 222507 (2009)

[6] H.N. Bertram and B. Lengsfield, IEEE Trans. Magn. 43, 2145 (2007)

15 Eylül, Perşembe, 15:30

Giovanni Finnochio,  Department of Material Physics and Electronic Engineering, Faculty of Engineering, University of Messina ; Italy

Resonant Effect in the presence of spin transfer torque


In this talk I will present some of the recent resonant effects observed in spintronic devices in the presence of spin-transfer torque.
I will discuss in detail the resonant switching , the isochronous and non-isochronous locking and the stochastic resonance. Analytical and numerical models will
be presented in comparison with the experimental data.



1996 – 2001 Degree in Electronic Engineering – Summa cum Laude;

Thesis on Ferromagnetism and Hysteresis model based on Preisach Formalism. The thesis has been developed in part at the Laboratory of Magnetism at University of Perugia , Italy .

2002 – 2005 PhD in “Advanced technologies for optoelectronics, photonics and electromagnetic modeling”. Thesis on Macromagnetic and micromagnetic modeling of ferromagnets, nanomagnetism and spintronics.” – University of Messina . Note: During my PhD course and the post-doctorate, I spent time at Universidad de Salamanca , Spain (theoretical group of Prof. Luis Torres) and at Cornell University , NY , USA (experimental groups of Profs. Daniel Ralph and Robert Buhrmam).


2008 – 2010 Senior Research Associate in Compuıtational Magnetism and Spintronics, and Magnetic Material Modeling.

Department of Material Physics and Electronic Engineering.

University of Messina ; Italy .

2006 – 2007 Postdoctoral Research Associate in Spintronics and Micromagnetism.

Department of Material Physics and Electronic Engineering.

University of Messina ; Italy .

Actual research interests

Design and realization of simulation tool for spintronic devices. Modeling of materials for spintronic applications. Theoretical and applied spintronics. Nanomagnetism.

Spin-transfer torque effects.

Spintronic devices: Magnetoresistive Random Access Memory design, Nano-oscillators, Microwave detectors.

Modeling and characterizations of magnonic crystals.

Non-linear phenomena in physical systems (injection locking, stochastic resonance,…).

Numerical computing and programming. Parallel computations on GPU-based technology (CUDATM).

Modeling of metamaterials for application in electromagnetism and seismic.

Biomedical applications of magnetoresistive devices.

Main scientific collaborations (active) with both experimentalist and theoretical groups and topic of collaboration

University of Perugia , Perugia ( Italy ); Prof. Ermanno Cardelli. – Modeling of Ferromagnets

Universidad de Salamanca, Salamanca ( Spain ); Prof. Luis Torres and Prof. Eduardo Martinez. Micromagnetism. Domain wall dynamics.

Cornell University , Ithaca , NY ( USA ); Prof. Dan Ralph and Prof. Robert Buhrman. – Spintronic devices: Magnetoresistive Random Access Memory design, Nano-oscillators, Microwave detectors. Applied Spintronics

Irvine University, Irvine, CA (USA); Prof. Ilya Krivorotov. – Spintronic devices: Magnetoresistive Random Access Memory design, Nano-oscillators, Microwave detectors.

Bogazici University , Istanbul , ( Turkey ); Prof. Ozhan Ozatay. – Modeling of materials for Spintronic applications.

Royal Institute of Technology, Stockholm , ( Sweden ); Prof. Johan Åkerman. – Applied Spintronics

Polytechnic University of Turin, Turin (Italy); Prof. Carlo Ragusa. – Magnonics

National Institute of Research in Metrology (INRIM), Electromagnetism Division; Turin (Italy), Dr. Paola Tiberto. – Magnonics

City University of Hong Kong, (Hong Kong), Prof. Antonio Ruotolo, Department of Physics and Materials Science. – Thermal spin-torque


University of Messina. Young Research Prize for the scientific results of the academic year 2007.