Magnets hold great allure for those at both ends of the age spectrum – be they Ph.D-holding physicists studying particle accelerators like CERN or three-year-old children discovering refrigerator magnets.
Magnets attract or repel each other based on the alignment of their poles. Every magnet has two magnetic poles called North and South that must line up correctly for magnets to attract or repel one another.
Electrons
Have you ever been curious as to why magnets stick together? It all boils down to electrons. Electrons are charged particles attached to all atoms in our environment, including metals like iron and copper, with built-in properties called spin that allow them to rotate as they move, producing magnetic forces as a result of their spinning movements.
All magnets contain two poles – north and south – which attract each other when placed side-by-side, and repel each other when separated from one another. They can even be combined together into cubes that act like magnets!
The magnetic cube is an invaluable teaching tool that can introduce students to magnetism. Students will understand that like poles repel while unlike poles attract, and magnetic fields extend in all directions.
Mess-free and safe, all iron filings are sealed inside an acrylic box that's easy to access and shake. Just drop a cylindrical magnet into its center compartment and watch as its presence causes reactions within the iron filings – perfect for exploring variables!
Researchers have developed a set of cube-shaped magnetic building blocks that can be assembled into two-dimensional shapes with ease and controlled by external magnetic fields. The modules developed by researchers – known as “modules” by their scientists – are not dipolar but instead quadrupolar; each module houses two conventional dipole magnets for use as soft robotics for drug delivery or cell measurement or even as miniature actuators.
Magnetism
Students may be familiar with magnets being drawn towards materials like white boards and fridges, yet few students have explored how magnets repel one another. Unfortunately, many classroom fridge magnets lack identifiable north and south poles making it challenging to conduct studies into magnetic forces.
Students often mistake magnetic and electrostatic forces as one, given they both act as non-contact invisible forces. It is essential for students to recognize that these two forms of force exist independently from each other and learn how to distinguish between them when conducting investigations.
Magnetism is caused by unpaired electrons in atoms acting on each other and moving freely within an electric current or, in certain instances, orbiting around their respective nuclei to generate magnetic moments in each electron – giving each one its own magnetic moment.
Magnets make some metals magnetic, while others are diamagnetic and don't react at all to magnets. Magnets also possess an invisible field surrounding them that attracts or repels magnetic objects according to their north and south poles – much like protons attract or repel electrons based on their north/south magnetic poles. When similar magnetic poles attract each other more strongly, then attraction increases, while when similar poles repel each other more strongly then repulsion increases further.
Dipolar
Magnets that possess non-randomly aligned dipole moments are said to possess ferromagnetism. Aligning dipole moments creates an ordered magnetic state known as ferromagnetism; alignment occurs due to either internal field interaction between dipoles or exchange interactions among dipoles; both mean field theory and Heisenberg exchange theory can explain this T-dependent magnetization characteristic of ferromagnets, meaning their magnetization changes with temperature.
Ferromagnetics can be magnetized backwards by applying an electric current that cuts across their atomic dipoles, yet this reversal may only partially reverse their magnetization due to orbitals' shapes being related to rotational angular momentum; consequently, there remains some level of magnetism produced by their own orbitals themselves and this generates a slight magnetic field as well.
Dipole magnetic fields produce vertical magnetic field gradients along their polar axis and horizontal along their equator, giving rise to geomagnetic equator and pole definitions that rely on locations of two magnetic dipoles overlapping each other.
Hysteresis of macroscopic spontaneous magnetization presents a major barrier to direct electric control of spin-polarized electrons. Although numerous methods have been proposed for overcoming this hurdle, most require significant amounts of energy and do not meet our requirements for controllability, accuracy and efficiency.
Quadrupolar
When an electron or proton comes close to another charged particle with similar polarity, they exert a force equal to Coulomb's law. But when two such charges get closer than this distance apart, their force increases exponentially (see illustration below) because their dipole moments cancel each other out, creating a quadrupole moment instead. When four identical bar magnets with their north poles close together are placed side-by-side next to one another, their combined dipole moment cancels faster than any one dipole's force does.
As quadrupolar broadening obscures other interactions, in order to resolve NMR experiments on quadrupolar nuclei they require high magnetic field strengths – however this comes at the cost of increased energy loss and thus less usable signal.
One solution to this conundrum is increasing the size of a quadrupole magnet, but this adds expense. Another approach involves changing the shape of the vacuum window in a field clamp vacuum chamber in order to decrease quadrupolar patterns by changing their orientation – different shapes have been tried, with tapered rectangles following pole shapes having proved most successful as these can significantly decrease second-order broadening effects despite not completely eliminating second-order broadening altogether. But there remains room for further optimization.
