Ferrite Magnet Squareness: Does the Hk to Hcj Ratio Matter for High-Current Use

If you work with ferrite permanent magnets, you may have come across the term “squareness” – often written as Hk/Hcj. It tells you how sharply the magnet resists demagnetization near the knee of the demagnetization curve. A higher number usually means a “squarer” loop.

So what’s considered acceptable? For many ferrite grades, an Hk/Hcj value of around 0.85 or above is generally seen as decent. Some lower‑cost materials might fall to 0.80 or slightly below, and they can still work in mild conditions. However, if the ratio drops under 0.75 – and especially below 0.70 – the magnet may become noticeably softer under strong demagnetizing fields.

Why does that matter in high‑current scenarios? In motors or solenoids, high current creates a strong opposing magnetic field. If the ferrite magnet has poor squareness, it can start to lose flux irreversibly during current peaks. That could mean a drop in torque, efficiency, or even partial demagnetization over time. The effect is not always instant, but it tends to accumulate with repeated high‑current pulses.

The good news is that manufacturers usually specify Hk/Hcj on data sheets. When design for demanding current loads, choosing a magnet with squareness above 0.85 is a reasonable solution. And if you have samples, a quick pulsed‑field test can tell you how they behave under stress. No single number guarantees perfect performance, but squareness is definitely worth a look when pushing current limits.