“How Magnets Work II”
IN this technological world, the majority of today’s electronic devices require magnets to function. This reliance on magnets is relatively recent, primarily because most modern devices require magnets that are stronger than the ones found in nature.
Lodestone, a form of magnetite, is the strongest naturally-occurring magnet. It can attract small objects, like paper clips and staples. By the 12th century, people had discovered that they could use lodestone to magnetize pieces of iron, creating a compass. Repeatedly rubbing lodestone along an iron needle in one direction magnetized the needle. It would then align itself in a north-south direction when suspended. Eventually, scientist William Gilbert explained that this north-south alignment of magnetized needles was due to the Earth behaving like an enormous magnet with north and south poles.
A compass needle isn’t nearly as strong as many of the permanent magnets used today. But the physical process that magnetizes compass needles and chunks of neodymium alloy is essentially the same. It relies on microscopic regions known as magnetic domains, which are part of the physical structure of ferromagnetic materials, like iron, cobalt and nickel. Each domain is essentially a tiny, self-contained magnet with a north and South Pole. In an un-magnetized ferromagnetic material, each of the north poles points in a random direction. Magnetic domains that are oriented in opposite directions cancel one another out, so the material does not produce a net magnetic field.
In magnets, on the other hand, most or all of the magnetic domains point in the same direction. Rather than cancelling one another out, the microscopic magnetic fields combine to create one large magnetic field. The more domains point in the same direction, the stronger the overall field. Each domain’s magnetic field extends from its north pole into the south pole of the domain ahead of it. This helps to explain why breaking a magnet in half creates two smaller magnets with north and south poles. It also explains why opposite poles attract, the field lines leave the north pole of one magnet and naturally enter the south pole of another, essentially creating one larger magnet. Like poles repel each other because their lines of force are travelling in opposite directions, clashing with each other rather than moving together.
To make a magnet, all you have to do is encourage the magnetic domains in a piece of metal to point in the same direction. That’s what happens when you rub a needle with a magnet, this exposure to the magnetic field encourages the domains to align. Other ways to align magnetic domains in a piece of metal include;
Placing it in a strong magnetic field in a north-south direction; Holding it in a north-south direction and repeatedly striking it with a hammer, physically jarring the domains into a weak alignment passing an electrical current through it.
Two of these methods are among scientific theories about how lodestone forms in nature. Some scientists speculate magnetite becomes magnetic when struck by lightning. Others theorize that pieces of magnetite became magnets when the Earth was first formed. The domains aligned with the Earth’s magnetic field while iron oxide was molten and flexible. The most common method of making magnets today involves placing metal in a magnetic field. The field exerts torque on the material, encouraging the domains to align. There’s a slight delay, known as hysteresis, between the application of the field and the change in domains takes a few moments for the domains to start to move. (To Be Continued)