Magnetic circuits are fundamental in various electrical and electronic devices, from transformers and inductors to motors and generators. Understanding the common magnetic circuit structures is crucial for engineers and scientists involved in the design, analysis, and optimization of these devices. This article provides an in - depth exploration of common magnetic circuit structures, including their basic components, working principles, and applications. It covers simple magnetic circuits, compound magnetic circuits, and some special - purpose magnetic circuit designs.

1. Introduction
Sintered neodymium-iron-boron (NdFeB) magnets are the most powerful permanent magnets available, with applications spanning electric vehicles (EVs), wind turbines, aerospace systems, medical imaging (MRI), and consumer electronics. Their performance—defined by magnetic properties (remanence, coercivity, energy product), thermal stability, corrosion resistance, and mechanical durability—is influenced by composition, microstructure, manufacturing processes, and environmental conditions.

This analysis explores the key factors affecting NdFeB magnet performance, their underlying mechanisms, and optimization strategies to enhance reliability and efficiency in high-demand applications.

Sintered neodymium-iron-boron (NdFeB) magnets, recognized as the strongest permanent magnets globally, are indispensable in high-performance applications such as electric vehicles, wind turbines, aerospace systems, and medical imaging devices. Their exceptional magnetic properties—including high remanence (Br), coercivity (Hcj), and maximum energy product ((BH)max)—stem from a complex manufacturing process involving powder metallurgy, magnetic field alignment, vacuum sintering, and precision machining. However, ensuring these magnets meet stringent performance and reliability standards requires rigorous testing across multiple dimensions. This guide details the critical testing items for sintered NdFeB magnets, categorized into dimensional accuracy, physical properties, magnetic characterization, microstructural analysis, environmental durability, and coating quality, with insights into methodologies, equipment, and industry standards.

Neodymium magnets (NdFeB), renowned for their exceptional magnetic properties, are widely utilized in high-tech applications such as electric vehicles, wind turbines, and medical devices. However, their susceptibility to corrosion, particularly in humid or aggressive environments, poses a significant challenge to their long-term performance. Passivation, as a surface treatment technique, offers an effective solution by forming a protective oxide layer on the magnet surface. This paper provides a comprehensive analysis of passivation technology for neodymium magnets, covering its principles, processes, advantages, limitations, and applications.

1. Introduction
Magnetic fields are ubiquitous in the physical world, playing a crucial role in various phenomena ranging from the behavior of elementary particles to the operation of large - scale electrical devices. Understanding how to calculate magnetic fields is fundamental in physics, engineering, and many applied sciences. This text will delve into the principles, formulas, and methods for calculating magnetic fields in different scenarios.

This paper delves into the critical concepts of the Curie temperature and working temperature of magnets, which are fundamental to understanding the behavior and performance of magnetic materials. The Curie temperature marks the phase transition point where a ferromagnetic material loses its permanent magnetic properties and becomes paramagnetic. The working temperature, on the other hand, is the range within which a magnet can maintain its specified magnetic performance. We will explore the underlying physics, factors influencing these temperatures, different types of magnets and their characteristic temperature ranges, the impact of temperature on magnetic properties, and practical applications where temperature considerations are crucial. By the end of this paper, readers will have a comprehensive understanding of how temperature affects magnets and how to select and use magnets based on temperature requirements.

NdFeB (Neodymium-Iron-Boron) magnets are widely used in various industries due to their high magnetic energy product and excellent magnetic properties. However, they are prone to corrosion because of their active chemical composition. To enhance their corrosion resistance and extend their service life, surface coatings are applied. This paper provides a comprehensive guide on how to choose the appropriate coating for NdFeB magnets, considering factors such as the application environment, cost, magnetic performance requirements, and processing complexity.

The hysteresis loop curve is a fundamental graphical representation in the study of magnetic materials. It provides crucial insights into the magnetic behavior of materials, including their energy - loss characteristics, remanence, and coercivity. This paper begins with an introduction to the basic concepts of magnetism and the need for understanding hysteresis. It then delves into the detailed construction of the hysteresis loop curve, explaining the different stages involved in the magnetization and demagnetization processes. The physical mechanisms underlying hysteresis, such as domain wall motion and magnetic moment rotation, are discussed. The paper also explores the factors affecting the shape and size of the hysteresis loop, including material composition, temperature, and grain size. Furthermore, it examines the applications of hysteresis loop analysis in various fields, such as electrical engineering, magnetic storage, and medicine. Finally, recent advancements and future research directions in the study of hysteresis loops are presented.

This paper delves into the intricate concepts of the orientation of magnets and the direction of magnetization. It begins by providing a fundamental understanding of magnetic fields, magnetic moments, and the basic properties of magnets. Subsequently, it explores the various factors that influence the orientation of a magnet, including external magnetic fields, geometric shapes, and material properties. The direction of magnetization is then thoroughly examined, covering the processes involved in magnetizing a material, such as alignment of magnetic domains, and the different methods used to achieve magnetization, like using solenoids and permanent - magnet fields. The paper also discusses the applications of these concepts in different industries, including electronics, medicine, and energy. Finally, it presents some recent advancements and future prospects in the field of magnet orientation and magnetization.

Abstract
Neodymium iron boron (NdFeB) permanent magnets, renowned for their exceptional magnetic properties, are indispensable in high-tech industries such as electric vehicles, wind turbines, and medical imaging. However, their susceptibility to corrosion—stemming from the reactive nature of neodymium and the porous microstructure of sintered NdFeB—poses significant challenges to longevity and performance. Phosphating treatment, a chemical conversion coating process, has emerged as a cost-effective and versatile solution for enhancing corrosion resistance and surface compatibility. This review systematically examines the principles, processes, performance optimization, and industrial applications of phosphating for NdFeB magnets, integrating mechanistic insights, experimental data, and case studies from recent research.