The proportioning of permanent magnets, that is the ratio of the magnet pole areas to the magnet thickness (L/D-ratio) of any magnet material, is subject to the laws of physics.
The maximum operating temperature also depends on the L/D-ratio. A thin NeoDelta magnet disc of 15 Ø x 2 mm e. g. can only be used up to a maximum operating temperature of + 70°C, whereas a thicker disc of 15 Ø x 8 mm can be used up to approx. + 100°C.
In the case of most modern magnet materials the remanence and the coercivity decreases on warming. When the temperature drops both values rise. This generally means that there is an improvement in most magnet systems up to - 40°C. SmCo magnets can be used for example in temperature areas below zero, which are necessary for the production of superconductors.
The magnetisation of rod magnets with a kept-in preference direction (anisotropy) during production is possible only in the preference direction.
It is not possible to state the holding force of an "open" permanent magnet. The "open" permanent magnet is surrounded by a magnet field of differing densities. This holding force is essentially determined by the magnetic effect on the iron to which the magnet is fixed. A thin iron plate has less force than a flat bar. A great variety of special magnets for adhesion to iron or steel for which all the magnetic energy will be concentrated on the active surface using iron poles are available.
High-energy magnets made from NeoDeltaMagnet (NdFeB) have to be stored dry, otherwise the surfaces would oxidise. Storage in a hydrogen atmosphere destroys these magnets. A demagnetisation is caused when permanent magnet materials have been exposed to radioactivity over a long period.
Small hairline cracks and cracks on the edges of sintered permanent magnets are not always avoidable during production. This does not affect the magnetic values, and should therefore be tolerated and accepted on purchase.
All sintered permanent magnets are hard and brittle. They split into many sharp-edged fragments when colliding with each other as a result of magnetic attraction. This especially occurs with high-energy magnets, and can also cause injury when there are high attraction forces.
Permanent magnets are surrounded by magnetic fields. These magnetic fields can disturb and even destroy sensitive electronic measuring devices as well as mechanical watches. Usually a distance of 0.5 m is enough to avoid damage. Persons with cardiac pacemakers should completely avoid magnetic fields.
Harmful effects of magnetic fields,like those of permanent magnets, on the human body are not known. Tests are currently being conducted into the effects on the human body of very high magnetic fields over 3 Tesla. In naturopathy and empirical medicine magnetism is used to cure illnesses. Even Paracelsus described the use of permanent magnets in his work. Later, Mesmer (1734 - 1815) formulated a theory on how to cure illnesses using magnetism. Except for a few applications, the cure using magnetism is not acknowledged by mainstream conventional medicine.