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A hysteresis loop (or B-H loop) is a four-quadrant graphical plot depicting the non-linear relationship between induced magnetic flux density (B) and applied magnetizing force (H). It illustrates how a ferromagnetic or ferrimagnetic material magnetizes, retains magnetism, and demagnetizes when exposed to an alternating magnetic field.
Industrial Applications
In magnetic engineering, hysteresis loops are measured using a hysteresigraph (B-H tracer) or Vibrating Sample Magnetometer (VSM) to characterize raw materials and evaluate performance in production. The loop's shape determines whether a material should be deployed as a "soft" magnetic core (narrow loop for easy magnetization) or a "hard" permanent magnet (wide loop for resistance to demagnetization). The total area enclosed by the loop represents hysteresis loss (energy converted into waste heat per magnetization cycle) which engineers minimize when designing high-efficiency electric motors, magnetic torque couplings, and transformers. For permanent magnet design, engineers focus heavily on the second quadrant (the demagnetization curve) to ensure custom assemblies maintain field strength without suffering irreversible demagnetization under opposing fields or elevated operating temperatures.
Technical Specifications
Core Variables & Units:
B: Magnetic Flux Density, measured in Tesla (T) or Gauss (G).
H: Magnetizing Field Intensity, measured in Amperes per meter (A/m) or Oersteds (Oe).
Br: Remanence or Retentivity (the residual magnetic flux remaining when H = 0).
Hc / Hci: Normal / Intrinsic Coercivity (the reverse magnetic field required to reduce flux density or internal polarization back to zero).
(BH)max: Maximum Energy Product, indicating the magnetic energy stored per unit volume (MGOe or kJ/m³).
Hysteresis Loss Formula:
Energy loss per cycle per unit volume (Wh) is equal to the closed loop:
Manufacturing & Testing Challenges:
Incomplete Saturation: If the applied field H during initial factory magnetization fails to reach true saturation, the material operates on a minor hysteresis loop, leading to substandard Br and inconsistent total flux output.
Thermal Degradation: Elevated operating temperatures shrink the hysteresis loop area, lowering both Br and Hci and increasing susceptibility to demagnetization under load for most rare-earth materials (NdFeB, SmCo).
Related Case Studies and Products
Technical Guide: Read a practical breakdown of second-quadrant demagnetization behavior in The Curve That Tells You Everything: BH Curves for Non-Engineers.
Engineering Capabilities: Evaluate high-coercivity materials and thermal stability via FEA Modeling & Material Selection.
Application Case Study: Learn how precision hysteresis analysis ensures magnetic uniformity in custom dipole systems in Engineering High-Volume Magnetic Uniformity for Advanced Thermal Processing.
Ready to Optimize Your Magnetic Circuit?
Whether you are selecting soft core materials to minimize hysteresis loss or engineering permanent magnet assemblies to withstand harsh demagnetizing fields, QT Magnetic Solutions provides complete FEA modeling, design for manufacturability (DFM), and fabrication. Contact QT Magnetic Solutions today to consult with our Silicon Valley engineering team.