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Lectures on Nanomagnetism
Prof. M. Farle
www.unidue.de/agfarle

University DuisburgEssen
(Lectures will be given in English with (partial) Russian translation upon request) th

Lecture Hall: library of faculty of physics, 5 floor

Monday, 24.03.2014 Duration 30 min 15:15 15:45 30 min 15:45 16:15 30 min 16:15 16:45 break 45 min 17:00 ­ 17:45 45 min 17:45 ­ 18:30 Tuesday, 25.03.2014 45 min 15:15 ­ 16:00 45 min 16:00 ­ 16:45 break 45 min 17:00 ­ 17:45

Title of Lecture Center of NanoIntegration at University of DuisburgEssen (Opportunities for joint research and visits) Nanomagnetism: Fundamentals Ia Nanomagnetism: Fundamentals Ib Discussions and Questions Nanomagnetism: Fundamentals II Nanomagnetism: Fundamentals II

Nanomagnetism: Experimental Techniques Ia Nanomagnetism: Experimental Techniques Ib Discussion and Questions Nanomagnetism: Experimental Techniques II Spin Dynamics and Magnetization Relaxation Ferromagnetic Resonance / Magnetic Damping

Wednesday, 26.03.2014 60 min 17:00 18:00

How to present scientific results professionally: Layout of Transparencies, body language, (video taped exercises for self evaluation)

Thursday, 27.03.2014 45 min 15:15 ­ 16:00

45 min 45 min 45 min 30 min

16:00­ 16:45 break 17:00 ­ 17:45 17:45 ­ 18:30 18:30 ­ 19:00

How to analyse a single magnetic nanoparticle ? requirements, sample preparation, structure and composition How to analyse a single magnetic nanoparticle ? static magnetic analysis, magnetic moments Discussion and Questions Nanomagnetism: Spin Torque Phenomena I Nanomagnetism: Spin Torque Phenomena II Future Challenges in Nanomagnetism

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Lectures: Nanomagnetism/ Fundamentals I and II
1. Introduction a. Diamagnetism b. Paramagnetism c. Ferro, Ferri and Antiferromagnetism d. Magnetic susceptibility and permeability 2. Magnetic order and magnetic interactions a. Magnetic exchange (direct, indirect, and superexchange) b. Dipolar magnetic interaction c. Spinorbit interaction d. Local magnetic moments and spinpolarized electron band structure 3. Magnetization and magnetic anisotropy of ferromagnets a. Magnetic hysteresis loop b. Magnetic anisotropy energy density (surface, volume, shape) c. Magnetic domains (competing exchange, magnetostatics and anisotropy) d. Temperature dependent magnetization e. Temperature dependent magnetic anisotropy 4. Superparamagnetism a. Magnetic moment of a single atom versus the magnetic moment of a nanoparticle b. Size dependence of the magnetization of a single nanoparticle c. Temperature dependence of the magnetization of a single nanoparticle d. Magnetic response of an ensemble of nanoparticles with different sizes Abstract: The fundamentals for understanding the magnetic response of a collection of magnetic nanoparticles and thin films are discussed. Starting with a review of the properties of dia, para and ferromagnetic materials an understanding for the magnetic stability of magnetic nanoparticles of different sizes, shapes, crystal structure and composition is developed. The dominating inner particles and interparticle magnetic interaction are presented. Within this frame of reference the behaviour of a nanoparticles ensemble is discussed. The concept of effective magnetic anisotropy and blocking temperature is explained. Finally, using this fundamental understanding the possibilities to tune and control the magnetic properties of nanoscale particles is presented. Suggested Reading: · Ch. Kittel, "Introduction to Solid State Physics", Chapter 11,12 and 13 · R. C. O'Handley, ,,Modern magnetic materials: Principles and Applications"

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Lectures: Nanomagnetism / Experimental Techniques I, II, and III



1. Overview a. Contributions to magnetization in a multielement material b. Extracting magnetic moments from magnetometry c. Problems when analysing magnetic hysteresis of unknown magnets d. How to measure magnetic susceptibility ? 2. Magnetometry a. Super conducting interference device (SQUID) magnetometry Artifacts , sensitivity and speed of different types of measurements b. Alternative methods of conventional magnetometry Vibrating sample magnetometer Alternating Gradient magnetometer c) Magnetooptics 3. Magnetic anisotropy energy density a. Torque magnetometry b. Ferromagnetic resonance 4. Synchrotron based techniques a. Element specific magnetic moments from Xray magnetic circular dichroism b. Elementspecific electronic structure c. Sitespecific bonding and bond length determination 5. Examples of magnetic resonance in systems at the nanoscale a. Ferromagnetic resonance in ultrathin films b. Ferromagnetic resonance in coupled ultrathin films c. Ferromagnetic resonance in ensembles of magnetic nanoparticles d. Ferromagnetic resonance on single nanostructures 6. Overview of methods not discussed (e.g. electron and neutron spectroscopies) Abstract: Experimental techniques to investigate collective and individual static magnetic responses of superparamagnetic nanoparticle are presented. Problems, artifacts and sensitivity concerns are discussed. Suggestions for the best experimental techniques to address specific problems in nanomagnetism are given. Suggested reading:
· · · J. StЖhr and H.C. Siegmann, ,,Magnetism: from fundamentals to nanoscale dynamics", Chapter 10 NanoSQUIDS: in Supercond. Technol. 22 (2009) 064001 A closer look into magnetism: Opportunities with synchrotron radiation , IEEE Transactions on Magnetics 45 (2009) 15-57 Magnetism at the Nanoscale: the case of FePt, Modern Physics Letters B 21 (2007) 1111-1131

·



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Lectures: Nanomagnetism / Spin Torque Phenomena I and II
1. Introduction a. Giant magnetoresistance spintorque b. Spintorque and magnetic random access memory 2. Spintorque in vertical structures a. Basic phenomenon b. Currentinduce magnetization reversal in nanopillars 3. Mathematical description a. LandauLifshitz (LL) equation of motion b. Simple explanation of additive term to LL equation 4. Requirements for spintorque systems a. Electron scattering in ferromagnetic solids b. Requirements for magnetic and nonmagnetic layers in spintorque systems 5. Detection of spintorque damping by Ferromagnetic resonance 6. Spintorque oscillators a. Basic phenomenon b. Experimental detection (LockIn amplifier) 7. Spintorque in lateral structures a. Currentinduced domain wall motion b. influence of Oersted field Abstract: An introduction to the field of spintorque driven processes is given. Spinpolarized currents may give rise to magnetization reversal or magnetization precession (spintorque oscillators) within vertical nanopillar samples that consist of two magnetic layers separated by a nonferromagnetic one. The phenomena are described using simple models, recent experimental evidence is given and a connection to possible applications is made. The effort to reduce the critical current density is reviewed. Within lateral stripelike systems spintorque can be used to move domain walls. This effect is discussed and experimental evidence in polycrystalline materials as well as single crystalline materials is given.



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