Temperature changes and extreme temperatures can cause a magnet to lose some or all of its magnetic charge. Losses can be temporary or permanent, depending on the conditions. The reversible operating temperature for a magnet is the temperature at which the magnet will recover its attraction.
The short answer is no, there is no shield or substance that will effectively block magnetic fields as such. You can however redirect the magnetic field lines, which is what some people call magnetic shielding.
Permanent magnets can lose their magnetism if they are dropped or banged on enough to bump their domains out of alignment. Heating a magnet above the Curie temperature causes the magnetic domains to be disrupted permanently. Mild heating causes a reduction in the magnetism.
Self Demagnetization
If you store a bunch of magnets together or randomly rub magnets against each other, each will affect the other, changing the orientation of the magnetic dipoles and lessening the net magnetic field strength. A strong magnet can be used to demagnetize a weaker that has a lower coercive field.
At frequencies from 30 to 100 MHz, aluminum foil provides at least 85 dB of shielding effectiveness. Unfortunately, aluminum foil is extremely inadequate against low frequency magnetic fields, where thick steel or highly permeable ferrite material provides more adequate shielding.
Magnets lose their properties if they are heated, hammered or dropped from some height.
Answer and Explanation: Heating a bar magnet will weaken its magnetic field. This is because the magnetic field is dependent upon an arrangement of molecules and atoms that is orderly, and when the magnet is heated, these atoms have more energy and move into a more disorderly arrangement, thus weakening the field.
Humidity.
Because moisture leads to corrosion, magnets should ideally be stored and used in dry environments. Best practice: Control the humidity levels within your facility to keep moisture levels low. If the humidity can't be controlled, use magnets with coatings to prevent corrosion.
Temperature affects magnetism by either strengthening or weakening a magnet's attractive force. A magnet subjected to heat experiences a reduction in its magnetic field as the particles within the magnet are moving at an increasingly faster and more sporadic rate.
If you can find a very strong magnet, repeatedly rub it across your weakened magnet. The strong magnet will realign the magnetic domains inside the weakened magnet [source: Luminaltech]. Magnet stacking One way to make weak magnets stronger is by stacking more of them together.
Magnetic fields will pass through plastic, wood, aluminium and even lead as if it was not there. There is no material that will block magnetism. Ferrous materials such as iron, steel or nickel can conduct magnetic fields and redirect magnetism.
During everyday use, the magnet will be dropped and banged about. This jostles the magnetic domains and means that they gradually become jumbled up. The more often this happens, the weaker the magnet becomes.
Magnets are typically resistant to traumas causing shock or vibration, and will not lose magnetic strength when exposed to them. The exception to this is traumas that cause damage to the structure of the magnet.
When you place the north pole of one magnet near the south pole of another magnet, they are attracted to one another. When you place like poles of two magnets near each other (north to north or south to south), they will repel each other.
There are a few ways to remove a magnetic field from a permanent magnet. One of these methods requires increasing the temperature of the magnet. Another way to make a magnet lose its magnetic field is by hitting it.
Magnets loose their properties if they are heated, hammered or dropped from some height.
While steel is a common choice, other metals, such as brass, copper and aluminum can also be used to block or shield against magnetic fields, but they are not as effective as iron or steel. There are also specialized materials are specifically designed for magnetic shielding.
MuMetal® is the most widely used alloy for magnetic shielding purposes. Its composition of 80% nickel, 4.5% molybdenum and balance iron gives it highly permeable properties.
Diamagnets repel, and are repelled by a strong magnetic field. The electrons in a diamagnetic material rearrange their orbits slightly creating small persistent currents which oppose the external magnetic field. Two of the strongest diamagnetic materials are graphite and bismuth.
When a permanent magnet is exposed to increased temperatures for a length of time, the electrons will be forced out of alignment and the magnet will be demagnetized, either partially or completely. The resulting demagnetization may be reversible, or it may be irreversible.
Soft iron makes stronger magnetic field because it becomes a magnet itself when the current is flowing. Also, soft iron loses its magnetism as soon as the current stops flowing. Thus, soft iron easily magnetizes and demagnetizes. Hence, it is used as a core in making electromagnets.
Typical materials used for electromagnetic shielding include thin layer of metal, sheet metal, metal screen, and metal foam. Common sheet metals for shielding include copper, brass, nickel, silver, steel, and tin.