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I did a search and found zero threads dedicated to hysteresis loops. I would love to discuss them and how they can help us achieve OU. Please point out any mistakes I have made as I explain the basics.
First we will talk about homemade permanent magnets. Picture a weak magnet like a steel bolt that you have been able to magnetize by using another magnet. This bolt was magnetized because as you introduced a magnetic field to it the atoms in it lined up in such a way as to line up with the field you presented. When you removed that field, a good percentage of the atoms in the bolt stayed in their new orientation. This allowed the bolt to maintain some of the magnetic field. Pretty cool.
Next take your bolt and introduce your magnet again. Only this time flip your magnet around. After you remove the field you will see that your bolt is still magnetic, but with the opposite polarity. This is because the atoms flipped around and lined up with the magnetic field you introduced in the opposite direction. Note: Again some of the atoms returned to random position when you removed the magnet, but a good percentage of them stayed lined up, hence you still have a weak magnetic bolt.
What you didn't notice as you did this was that while you were changing the bolt's polarity from your original pole to the second pole, your magnet had to perform extra work. It took work to change the bolt from the first pole to neutral before it could change it from neutral to the new pole. Make sense?
Now, if you were to repeat this transition back and forth and plot the information on a graph you would have the hysteresis loop (also known as hysteresis curve).
Now let's refer to a picture.
The "E" axis represents the amount of magnetic force you used to influence the material. The D axis represents the magnetic field that is currently in the material.
Take note that when E = 0 it is as if there is no external magnetic field influencing the material (there is zero field influencing the material in either the north or south direction). How may points are there on the intercept when E = 0? ... Three.
This makes sense if you back up and think about our magnetic bolt. Before you made it magnetic it was neutral. This is the point in the middle at 0,0. But then you added a field and the bolt began to magnetize. The line grew until the field couldn't influence the bolt any more (see line DS in the picture). You then take the magnet away and the bolt begins to loose magnetism as some of the atoms return to random orientation. But if you follow the line back to where there is no external field again (E=0) you will see that there remains some magnetic charge in the bolt (point Dr). Dr represents the charge that is left in the bolt. It is the weak charge of your homemade magnet.
Next you introduce an opposite magnetic field. The line again begins to drop. Eventually at point Ec the bolt is back to a neutral charge and is not magnetic (notice though that you had to apply a certain amount of opposing force just to get it to neutral). You then continue to influence the bolt charging it in the second polarity until it can't be influenced any more. This is the same as line Ds, but with the opposite polarity. You remove the magnetic field and the line returns back to E=0 only this time it retains some of the negative polarity.
This loop will repeat over and over as you charge the material in opposing fields. If you only charge the material with one polarity the story changes a little. I will post more on that later...
So to help you understand, would you want a fat or a thin curve if you were trying to make a magnet? ... a fat one. Why? ... because it will hold more of the charge after you remove the external field.
Would you want a fat or thin curve if you were looking for a core material to make a motor? ... a thin one. Why? ... so you wont have to do as much work to return the material back to zero polarity every time you go through a cycle. That work is wasteful. It is lost as heat.
So in some situations you want a thin hysteresis loop, in others you want a fat one. It depends on what you are trying to accomplish.
Notice also that the slant of the loop can vary. We will discuss this later.
First we will talk about homemade permanent magnets. Picture a weak magnet like a steel bolt that you have been able to magnetize by using another magnet. This bolt was magnetized because as you introduced a magnetic field to it the atoms in it lined up in such a way as to line up with the field you presented. When you removed that field, a good percentage of the atoms in the bolt stayed in their new orientation. This allowed the bolt to maintain some of the magnetic field. Pretty cool.
Next take your bolt and introduce your magnet again. Only this time flip your magnet around. After you remove the field you will see that your bolt is still magnetic, but with the opposite polarity. This is because the atoms flipped around and lined up with the magnetic field you introduced in the opposite direction. Note: Again some of the atoms returned to random position when you removed the magnet, but a good percentage of them stayed lined up, hence you still have a weak magnetic bolt.
What you didn't notice as you did this was that while you were changing the bolt's polarity from your original pole to the second pole, your magnet had to perform extra work. It took work to change the bolt from the first pole to neutral before it could change it from neutral to the new pole. Make sense?
Now, if you were to repeat this transition back and forth and plot the information on a graph you would have the hysteresis loop (also known as hysteresis curve).
Now let's refer to a picture.
The "E" axis represents the amount of magnetic force you used to influence the material. The D axis represents the magnetic field that is currently in the material.
Take note that when E = 0 it is as if there is no external magnetic field influencing the material (there is zero field influencing the material in either the north or south direction). How may points are there on the intercept when E = 0? ... Three.
This makes sense if you back up and think about our magnetic bolt. Before you made it magnetic it was neutral. This is the point in the middle at 0,0. But then you added a field and the bolt began to magnetize. The line grew until the field couldn't influence the bolt any more (see line DS in the picture). You then take the magnet away and the bolt begins to loose magnetism as some of the atoms return to random orientation. But if you follow the line back to where there is no external field again (E=0) you will see that there remains some magnetic charge in the bolt (point Dr). Dr represents the charge that is left in the bolt. It is the weak charge of your homemade magnet.
Next you introduce an opposite magnetic field. The line again begins to drop. Eventually at point Ec the bolt is back to a neutral charge and is not magnetic (notice though that you had to apply a certain amount of opposing force just to get it to neutral). You then continue to influence the bolt charging it in the second polarity until it can't be influenced any more. This is the same as line Ds, but with the opposite polarity. You remove the magnetic field and the line returns back to E=0 only this time it retains some of the negative polarity.
This loop will repeat over and over as you charge the material in opposing fields. If you only charge the material with one polarity the story changes a little. I will post more on that later...
So to help you understand, would you want a fat or a thin curve if you were trying to make a magnet? ... a fat one. Why? ... because it will hold more of the charge after you remove the external field.
Would you want a fat or thin curve if you were looking for a core material to make a motor? ... a thin one. Why? ... so you wont have to do as much work to return the material back to zero polarity every time you go through a cycle. That work is wasteful. It is lost as heat.
So in some situations you want a thin hysteresis loop, in others you want a fat one. It depends on what you are trying to accomplish.
Notice also that the slant of the loop can vary. We will discuss this later.