Course Micromagnetics

This course was created to systematize and present material on micromagnetics in Russian (and eventually in English). In these videos, I want to compile information, much of which is scattered and only available in English. In creating the course, I drew on my personal experience and that of my colleagues using micromagnetic calculations in scientific research (relevant articles).

The course covers both theoretical and practical aspects of micromagnetics, i.e., Theory complements Practice: finding an analytical solution to a problem followed by its numerical modeling.

I’m also publishing and updating a list of lectures with brief descriptions here to make it easier for you to navigate the course with its non-standard numbering 😊 I also share plans for future lectures.

Regarding numbering. Some videos have a double number. This means that the topic is split into two or more videos: theory and practice. Video #0 is introductory and contains the main  sources of information (books, videos, presentations). Some lectures also feature additional sources that better address a specific topic.

You can always support the work on the course and simply say “thank you” by citing my articles and with a donation on Boosty.

Course outline

0. Introduction. Sources of information
1. Scales in micromagnetics and its place in magnetism
2. Practical Micromagnetics (the most important lecture of the course)
3.1. Magnetic hysteresis, theory
3.2. Workshop: Hysteresis in Boris Spintronics
4.1 Domain walls, theory
4.2. Workshop: Domain walls in Boris Spintronics
5.1. Magnetic domain visualization methods

Sources of information

Plans:
5.2 Topological magnetic defects and structures
5.3 Workshop: micromagnetic modeling of a multidomain state
6.1. Ferromagnetic resonance (FMR), theory
6.2. FMR calculation in Boris Spintronics
7.1. Spin waves, theory
7.2. Spin waves modeling and their dispersion
8.1. Introduction to spintronics
8.2. Spin current modeling in Boris Spintronics
… something else 🙂

0. Introduction. Sources of information

Pilot series: what this course is about, what sources of information were used, what will happen next.
Links to resources from the presentation.

1. Scales in micromagnetics and its place in magnetism

When and why did micromagnetics appear, what was there before, where is it now, what are the typical scales of space and time in it. Interesting video about the Chinese emperor and the magnetic gates.
00:00 – Introduction
00:47 – Brief History of Magnetism
09:07 – The Place of Micromagnetics in Magnetism
12:42 – Spatial Scales in Micromagnetics
16:00 – Temporal Scales in Micromagnetics
17:23 – Numerical Micromagnetism Today (Examples)
26:12 – Conclusion

2. Practical micromagnetics

The most important lecture

I discuss the pitfalls of practical calculations, provide an overview of packages and approaches to micromagnetic modeling, briefly demonstrate the types of Landau-Lifshitz equations, share useful links and lab developments, and compare real physics and a computer model.
01:17 – Landau-Lifshitz equation
02:29 – Free energy
08:04 – Extensions of the LL equation
13:00 – Software for micromagnetic modeling
17:28 – Classification of problems for micromagnetic modeling
20:16 – Solving dynamic and static problems
25:17 – Calculating spin wave dispersion and inverse problems
27:32 – Choosing the size and number of cells
36:52 – Symmetry breaking
39:14 – Field step and stopping criteria
41:02 – Solution correctness criterion

3.1 Magnetic hysteresis, theory

The problem of minimizing the energy of a magnetic particle in a single-domain state in the Stoner-Wohlfarth model is considered theoretically, an expression for the coercivity field is obtained, and the particle sizes for stable multi-, single-domain, and superparamagnetic states are qualitatively determined.
00:00 Introduction
01:09 Energy of a Magnet
03:18 Magnetic Domains
04:24 Single-Domain Particle
06:10 Shape Anisotropy
10:20 Stoner-Wohlfarth Hysteresis
20:10 Anisotropy Field
21:44 Multi-Domain Sample
25:25 Superparamagnetism

3.2 Hysteresis in Boris Spintronics

Overview  of Boris Spintronics software and hysteresis calculation for NIST Standard Problem 1
03:56 Boris Software Overview
06:16 Equilibrium State Calculation for Standard Problem 1
10:47 Geometry Definition
13:55 Material Parameters: Magnetization, Anisotropy, etc.
16:48 Free Energy Contributions
18:58 Saving Data
21:54 Solver Parameters
24:11 Calculation Steps
25:32 Simulation Start
26:28 Display
27:19 Initial Magnetization Configuration
32:26 Hysteresis Calculation
45:47 Demagnetization Energy
50:29 Data Plotting

4.1 Domain walls

In the continuum approximation of micromagnetics, the formation of magnetic domain walls is considered as a function of the ratio of exchange parameters and magnetic anisotropy. A formula for the thickness of Bloch- and Néel-type domain walls is derived, and the conditions for the occurrence of one or another type in thin magnetic films are identified.
00:05 Introduction to magnetic domains
03:40 Barkhausen effect
06:59 Magnetostatic equations / magnetostatic charges
10:01 Weiss domains
13:09 Landau-Lifshitz structure
13:43 Observation of domain walls
16:20 Domain wall structure
24:17 Domain wall width
26:37 Domain walls in thin films

4.2 Domain walls in Boris Spintronics

Workshop about Boris Spintronics and modeling magnetic domain walls in a thin ferromagnetic strip. Energies exchange, magnetic anisotropy, and demagnetization are considered. The domain wall is stabilized by two external magnetic dipoles with corresponding boundary conditions.
00:05 Introduction, Review
05:23 Domain Walls in Microstrips
06:42 Workshop Outline
09:09 Geometry Definition
10:25 Domain Wall Definition
15:26 Adding Fixed Dipoles
25:17 Saving and Constructing a Spatial Magnetization Profile
30:24 Magnetic Vortex Definition

5.1. Magnetic domain visualization methods

In this video, we’ll explore various methods for visualizing magnetic domains and domain walls, including exotic ones for the most complex magnetic structures. Discover the power of magneto-optics and other techniques that allow you to see the invisible! We’ll discuss methods from table-top setups to synchrotrons, from lasers to cantilevers. This lecture is quite an overview, ideal for students, researchers, and anyone interested in magnetism and its applications.
03:36 Classification of Methods and Their Characteristics
05:56 Powder Figure Method
07:00 Magneto-optical Effects
11:43 Magneto-optical Microscopy
16:52 Ultraviolet Range
19:01 X-ray Magnetic Dichroism (XMCD, XMLD)
21:51 Lorentz Transmission Electron Microscopy
26:13 Electron Holography
28:51 Scanning Electron Microscopy with Polarization Analysis (SEMPA)
30:58 Electron Diffraction
32:30 Magnetic Force Microscopy
37:06 Scanning Near-Field Optical Microscopy (SNOM)
39:05 Magnetometry at the NV Center in Diamond
45:02 Spintronic Effects, Exotics

My articles using micromagnetic calculations

I. A. Filatov, P. Gerevenkov, N. E. Khokhlov, and A. M. Kalashnikova, “Tunable quasi-discrete spectrum of spin waves excited by periodic laser patterns,” Journal of Applied Physics, vol. 136, no. 6, 2024. doi: 10.1063/5.0216091.

N. E. Khokhlov, I. A. Filatov, and A. Kalashnikova, “Spatial asymmetry of optically excited spin waves in anisotropic ferromagnetic film,” Journal of Magnetism and Magnetic Materials, vol. 589, p. 171 514, 2024. doi: 10.1016/j.jmmm.2023.171514.

A. Fedianin, N. E. Khokhlov, and A. Kalashnikova, “Propagation of a laser-induced magnetostatic wave packet in a pseudo spin valve in the presence of spin pumping,” Journal of Experimental and Theoretical Physics, vol. 137, no. 4, pp. 453–462, 2023. doi: 10.1134/S1063776123100035.

P. Gerevenkov, I. A. Filatov, A. Kalashnikova, and N. E. Khokhlov, “Unidirectional propagation of spin waves excited by femtosecond laser pulses in a planar waveguide,” Physical Review Applied, vol. 19, no. 2, p. 024 062, 2023 doi: 10.1103/PhysRevApplied.19.024062.

N. E. Khokhlov, A. Khramova, I. A. Filatov, P. Gerevenkov, B. Klinskaya, and A. Kalashnikova, “Néel domain wall as a tunable filter for optically excited magnetostaticwaves,” Journal of Magnetism and Magnetic  aterials, vol. 534, p. 168 018, 2021. doi: 10.1016/j.jmmm.2021.168018.