Hey everyone, it’s Jake here—head of product over at Bar Magnets Co. I’ve been geeking out with magnets for over a decade, and the question I get most from customers, especially when they’re buying bulk bar magnets for projects, is: “What’s this magnetic hysteresis thing I keep seeing in specs?” It’s not just some jargon we throw around to sound smart—understanding it can save you money, help you pick the right magnet for your job, and even make your projects work way better. Let’s break this down like we’re grabbing a coffee and troubleshooting a project, no stuffy textbook jargon. Bar Magnets
First, let’s start with the basics everyone knows: a bar magnet has two poles, right? North and South, and that’s why it sticks to fridges, pulls on other magnets, and works in everything from motors to sensors. But here’s the thing—when you start talking about magnets as materials, not just the bar magnets you buy at a hobby shop, they don’t just snap into their magnetic state. That’s where hysteresis comes in. The fancy definition is something like “the lag between an applied magnetic field and the material’s resulting magnetization,” but let’s make it real.
Imagine you’ve got a blank, non-magnetic iron bar. You wrap a coil of wire around it, hook it up to a power supply, and turn on the electricity. That makes an external magnetic field around the iron—let’s call that the “applied field.” As you turn up the power (crank the field higher), the iron atoms’ tiny magnetic domains (think of them like tiny, little bar magnets inside the metal) start lining up. At first, they flip pretty easily, so the magnetization of the iron bar jumps up fast. But once most domains are lined up, cranking the power more barely changes how magnetized the bar gets—we hit what’s called saturation. That’s the max magnetization that iron can hold, no matter how much external field we throw at it.
Now, here’s the lag part. If you turn the power down, the domains don’t just flip back to zero right away. Some of them get stuck lined up, like how a couch cushion stays bent a little when you lean on it. So when the applied field goes back to zero, the iron bar is still magnetized—that’s why a plain iron bar can turn into a permanent bar magnet if you leave it in a strong field. That leftover magnetization is called remanence (or retentivity, if you wanna get technical). But if you want to demagnetize it, you don’t just turn the power off. You have to flip the direction of the external field (reverse the current in the coil) and slowly crank it up until the bar stops being magnetized. The amount of reverse field you need to wipe out all the magnetization is called coercivity.
All this back-and-forth—applied field going from positive to negative to positive, magnetization following behind, not matching exactly—makes a loop. We call this the hysteresis loop, and every magnetic material has its own unique shape for it. For bar magnets, that loop is super important because it’s what makes them permanent. Let’s cut to why this matters for you, especially if you’re buying bar magnets for industrial, commercial, or even big hobby projects.
Think of two common types of magnets we sell at Bar Magnets Co.: neodymium bar magnets and alnico bar magnets. Neodymium is that super strong rare-earth magnet you know that can lift 10x its weight. Its hysteresis loop is super wide—meaning it has super high coercivity. That means it takes a lot of reverse field to demagnetize it, so once it’s magnetized, it stays that way, even if you drop it (carefully) or expose it to weak external fields. Alnico bar magnets, on the other hand, have a narrower loop. They’re still strong, but they’re way more prone to losing their magnetism if they get hit with a reverse field or get too hot. That’s why you’d never use an alnico bar magnet in a high-torque motor, but they work great for things like guitar pickups where you want a more stable, consistent field over time.
Wait, let’s talk about a common mistake we see customers make all the time. Some folks think all bar magnets are the same, but their hysteresis curve is what separates the ones that’ll last 10 years vs. the ones that’ll fizzle out in a year. For example, if you’re making a custom sensor that needs a super consistent magnetic field—no fluctuations—you need a magnet with a straight, narrow hysteresis loop. That way, its magnetization won’t change even if it’s near other magnets or gets small temperature swings. If you grab a neodymium bar magnet, that’s exactly what you get. But if you use a cheaper ceramic bar magnet (another type we sell, by the way) for that job, its coercivity is lower, so over time, small external fields will nudge its domains around, and the field strength will drop.
Another real-world example: we had a customer last year who was making custom door latches for commercial fridges. They initially bought ceramic bar magnets because they were cheaper, but within 6 months, half the latches weren’t sticking. Turns out, the fridges had compressors with strong magnetic fields nearby that were slowly demagnetizing the ceramic magnets—their narrow hysteresis loop couldn’t hold up to that. They switched to our neodymium bar magnets, which have way higher coercivity, and they haven’t had a single issue since. That’s the kind of problem hysteresis is directly responsible for, and it’s why paying attention to it (instead of just going for the lowest price) saves you a ton of headaches and rework.
Now, let’s get back to that hysteresis loop for a sec, because it’s not just about materials. The energy lost when you cycle the magnetic field back and forth is called hysteresis loss. That’s a big deal for motors and generators, right? Every time a magnetic material flips its domains, it uses a tiny bit of energy, which turns into heat. For bar magnets that are in static use—like fridge magnets or shelf displays—this loss is basically zero, so you don’t have to worry about it. But if you’re using bar magnets in a rotating motor, that loss adds up over time. That’s why motor designers pick specific magnet materials with lower hysteresis loss to make their motors more efficient. At Bar Magnets Co., we work with a ton of motor engineers to pick the exact bar magnet material that balances strength, coercivity, and energy loss for their build.
Wait, let’s clear up a myth real quick. Some people think that hysteresis is a bad thing, but it’s all about context. For permanent bar magnets, we actually want high hysteresis—meaning they retain their magnetization, don’t demagnetize easily, and have a stable field. That’s a good thing. For electromagnets or transformers, we want low hysteresis so we don’t waste energy on heat. So it’s not a flaw in the material—it’s just a property that we design around for specific uses. That’s one of the coolest parts of working with magnets: the same property that makes bar magnets stick to your fridge is what makes motors run efficiently, depending on how you use it.
Let’s tie this back to our customers, because that’s who this is for. Whether you’re a small business owner making custom products, an engineer designing industrial equipment, a hobbyist building a robot, or someone just replacing a broken fridge magnet, understanding a bar magnet’s magnetic hysteresis will help you pick the right magnet for the job. If you need a magnet that’s tough, won’t lose strength, and works in tough conditions (high temps, near other magnets, heavy use), go for a rare-earth or alnico bar magnet—their wide hysteresis loops are built for that. If you need something cheap for a temporary project, a ceramic bar magnet might work, just know it’ll demagnetize over time in certain environments.
At Bar Magnets Co., we don’t just sell magnets—we help you pick the right ones. We’ve spent years testing different materials, tracking how their hysteresis curves perform in real-world use, and building relationships with customers who need specific magnet specs. A lot of suppliers will just sell you the cheapest bar magnet, but we’ll ask you questions like: Where will this magnet be used? What temperature will it be exposed to? How strong does the field need to stay? Those questions help us point you to the magnet with the perfect hysteresis properties for your project, so you don’t waste money on something too strong or end up with something that breaks after a few months.
Let’s do a quick recap to make sure we didn’t skip anything: Magnetic hysteresis is the lag between an applied magnetic field and a bar magnet’s resulting magnetization. It comes from the tiny atomic domains inside the metal that don’t line up perfectly when the field changes, and don’t flip back when the field is removed. This creates a hysteresis loop that’s unique to each magnet material, which tells you how well the magnet holds its strength (coercivity and remanence). For permanent bar magnets, high coercivity from a wide loop is a good thing—it means a long-lasting, stable magnet. For rotating equipment like motors, hysteresis loss is something to keep in mind to keep energy efficiency up.
If you’re in the market for bar magnets for any project—big or small—and you’re not sure which type is right for you, don’t second-guess it. Hysteresis is a super important property, but you don’t have to be a magnetic physicist to figure it out. Just reach out to our team here at Bar Magnets Co., tell us what you’re building, and we’ll hook you up with exactly the magnets you need. We’ve got bar magnets in all sizes, materials, and strengths, and we’re happy to walk you through all the specs, including their hysteresis characteristics, so you can make a confident purchase without the confusion. Stop guessing and start getting the right magnets for your project—we’re here to help.
Disc Magnets References
- Cullity, B. D., & Graham, C. D. (2009). Introduction to Magnetic Materials. Wiley.
- O’Handley, R. C. (2000). Modern Magnetic Materials: Principles and Applications. Wiley.
- Zurek, S., et al. (2018). Magnetic Hysteresis: From Fundamentals to Applications. IOP Publishing.
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