We investigate magnetization processes in various types of ferromagnetic materials. Detailed knowledge of such processes is required in order to predict response of the magnetic materials to external actions like application of magnetic field, loading the samples with mechanical stress, change of the temperature. We develop sensitive methods of non-destructive testing of such materials based on connections between the magnetization processes and microstructure of the materials. These methods are aimed at investigation of uniformity of the materials, at characterization and mapping of mechanical defects due to corrosion and/or to any other wear and tear of the materials in industrial service, at advance prediction of lifetime of constructions under cyclic loads, etc. We also contribute to the basic research in development of a general response theory of non-linear non-equilibrium systems, of which the ferromagnetic materials are subclass.

Facility

• Proprietary computer-steered permeameter collecting the general magnetic permeability data for their next processing by the Preisach model formalism. The set-up is based on the electromagnetic induction response of the investigated material to triangular variations of an applied magnetic field. The collected data represent dynamic and/or quasistatical general permeability response to the applied field.
• Proprietary computer-steered hysteresisgraph collecting the magnetic hysteresis loop data for their next processing by the Preisach model formalism. The set up is based on the integration of electromagnetic induction response of the investigated material to any shape of the applied magnetic field. The collected data represent quasistatical magnetization response to the applied field. The equipment is shared with the Group of Amorphous, Nanocrystalline and Nanocomposite Materials.
• Computer-steered vibrating sample magnetometer PAR 4500 collecting the magnetic hysteresis loop data on small-volume samples for their next processing by the Preisach model formalism. The equipment is shared with the Group of High-Temperature Superconductivity.
• Leitz polarizing microscopes, transmission and reflection, for comparative optical and magnetooptical inspection of the samples.

Research

Non destructive method of materials testing based on the Preisach model of hysteresis

Magnetization processes are sensitive to the macro- and micro-structure of investigated samples. Utilizing a systematic layout of magnetic data inspired by the Preisach model of hysteresis, we build portraits of magnetization processes in ferromagnetic construction materials subjected to different stresses, cyclic loads, partial phase transformations, etc., which modify the macro- and micro-structure of the investigated samples. The Preisach portraits are modified correspondingly. Based on these portraits we introduce integral parameters strongly correlated with the type and strength of changes the material underwent. In contrast to the parameters of the classical magnetic hysteresis methods, the Preisach-portrait-based integral parameters are optimized with respect to the specific structural variations of the samples, and they are characterized by their substantially larger sensitivity and selectivity than the classical ones.

Theoretical analysis of Preisach representations of model systems with hysteresis

This research is aimed at development of a response theory of non-linear non-equilibrium systems. The response of such systems usually shows hysteresis with a non-local memory, which principally can not be described by any differential constitutive law. Our work is based on the Preisach model of hysteresis, which is a particular type of spectral decomposition of the response operators. We are interested in establishing precise limits of applicability of the Preisach decomposition to dynamical systems, studying the connection between the system's random potential and its Preisach representation, the influence of long-range interactions on this representation, and connections between kinetics of thermal relaxation and the Preisach representation of the system's response.

Cooperation

• Research Institute for Technical Physics and Materials Science, Budapest, Hungary
• Ames Laboratory, Iowa State University, Ames, USA
• Materials Department, IEN Gallileo Ferraris, Torino, Italy
• Institute for Magnetics Research, The George Washington University, Washington, USA
• Department of Physics of Thin Films, Institute of Magnetism NAS Ukraine, Kiev, Ukraine