How Superconductors Behave in Magnetic Fields: Key Insights
Superconductivity was first found in 1911 when mercury was cooled to roughly 4 degrees Kelvin by Dutch physicist Heike Kamerlingh Onnes, which acquired him the 1913 Nobel Prize in material science. It is a material that is capable of superconducting at low temperatures.
A superconductor example is “Tungsten”, other examples are “Tin,”, “Zinc,” these materials are when cooled at a critical temperature, they suddenly become superconductors.
One of the known applications of a superconductor is, they are used in generating the mighty magnetic field between 20 - 30 T.
On this page, you will get sufficient information on superconductors, like the properties of superconductors and applications of superconductors.
Superconductor Materials
A superconductor is a component or metallic alloy which, when cooled under a specific limit temperature, the material significantly loses all electrical obstruction.
On a fundamental level, superconductors can permit electrical flow to stream with no energy loss (albeit, by and by, an ideal superconductor is difficult to produce). This kind of current is known as a supercurrent.
The critical/edge temperature beneath which a material changes into a superconductor state is assigned as Tc, which represents basic (critical) temperature. Not all materials transform into superconductors, and the materials that do, have their own value or estimation of Tc.
Examples of Superconducting Materials
The resistivity of most metals increments with expansion in temperature and the other way around. There are a few metals and chemical compounds whose resistivity becomes zero when their temperature is brought close to 0 Kelvin or - 273°C. At this stage, such metals or compounds are said to have achieved superconductivity.
For instance, Mercury becomes superconducting at around 4.5 Kelvin (- 268.5°C). The progress from typical conductivity to superconductivity happens unexpectedly; it happens over an exceptionally restricted range of temperature, i.e., about 0.05 K.
So, the temperature at which the progress happens from the condition of ordinary conductivity (such as Mercury, as mentioned above) to that of superconductivity is called transition/changing temperature.
Types of Superconductors
Superconductors are categorized into types: type 1 and type 2 superconductors.
Type 1 Superconductors
Type I superconductors are delicate superconductors. They are generally pure examples of certain components for example metals. They have almost no utilization in technical applications.
These types of superconductors act as conductors at room temperature, yet when cooled beneath Tc, the sub-atomic movement inside the material decreases sufficiently that the progression of current can move unobstructed.
Type 2 Superconductors
Type 2 superconductors are hard superconductors. They are typically combinations of metals with a high value of resistivity in ordinary states. These are valuable when contrasted with Type 1 materials.
Type 2 superconductors are not especially acceptable conductors at room temperature, the progress to a superconductor state is more continuous than Type 1 superconductors. The system and the actual reason for this adjustment in the state aren’t, as of now, completely comprehended. Type 2 superconductors are ordinarily metallic alloys and compounds.
Examples of superconducting materials of type 2 are niobium and vanadium.
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Magnetic and Electromagnetic Properties of Superconductors
The properties of superconductors lie hereunder:
1. Critical Field
Use of an adequately strong magnetic field to superconductors causes the obliteration/destruction of their superconductivity, i.e., the rebuilding of their normal conducting state.
The critical value of the magnetic field for the obliteration of superconductivity is meant by Hc and is practically identified with temperature as;
Hc = Hc (0) [1 - T2/Tc2]
Where
Hc(o) = critical field at 0 K, and has a particular value for every material.
Point to Note:
The lower the temperature, the higher the estimation of Hc and the most increased critical temperature happens when there is no magnetic field.
In this manner, we track down that the superconducting state is steady just in some definite ranges of magnetic fields and temperatures. For higher fields and temperatures, the ordinary state is more steady.
2. The Meissner Effect
As we stated above, a type 1 superconductor as a long, thin cylinder or ellipsoid remaining parts superconducting at a fixed temperature as an axially arranged magnetic field is applied, given the applied field doesn't surpass a critical value ( Hc).
Under these conditions, superconductors prohibit the magnetic field from their inside, as could be anticipated from the laws of electromagnetism and the way that the superconductor has no electric obstruction.
An amazing impact happens if the magnetic field is applied similarly to a similar sort of sample at a temperature over the transition temperature and is then held at a fixed value while the sample is cooled. It is tracked down that the example removes the magnetic flux, as it becomes superconducting. We call this effect the Meissner Effect.
3. High-Frequency Electromagnetic Properties
The energy gap in a superconductor directly affects the absorption of electromagnetic radiation. The photon's energy (E) is identified with its recurrence/frequency () by Planck’s relationship, E = hν.
Here,
"h" is Planck's steady (6.63 × 10−34 Joule-second). In the absorption process, a photon (a quantum of electromagnetic energy) is consumed, and a Cooper pair is broken; the two electrons in the pair become energized. At low temperatures, at which an immaterial part of the electrons are thermally excited to states over the gap, the superconductor can absorb energy just in a quantized sum that is, at any rate, double the gap energy (at total zero, 2Δ0).
Henceforth the superconductor can retain electromagnetic energy just for frequencies in any event as extensive as 2Δ0/h.
FAQs on Magnetic and Electromagnetic Properties of Superconductors
1. What are the key magnetic properties that define a superconductor?
A superconductor is defined by two fundamental magnetic properties:
- Perfect Diamagnetism (The Meissner Effect): This is the ability of a superconductor to completely expel all magnetic field lines from its interior when it is cooled below its critical temperature.
- Critical Magnetic Field (Hc): Superconductivity exists only up to a certain magnetic field strength. If the external field becomes stronger than this critical value, the material loses its superconducting properties and returns to a normal state.
2. What is the Meissner effect in simple terms?
The Meissner effect is the complete repulsion of a magnetic field from inside a superconductor. When a material becomes superconducting, it doesn't allow any magnetic field to pass through it. This powerful repulsion is what allows a lightweight magnet to levitate or float above a superconductor, a classic demonstration of this property.
3. How is a superconductor's magnetic behaviour different from a perfect conductor's?
This is a key difference. A perfect conductor (a hypothetical material with zero resistance) would simply trap any magnetic field that was present when it became conductive. In contrast, a superconductor actively pushes out any existing magnetic field when it cools down. This active expulsion, the Meissner effect, is unique to superconductors and proves they are more than just perfect conductors.
4. What are the main differences between Type I and Type II superconductors?
The main difference is how they respond to an increasing magnetic field:
- Type I superconductors exhibit a complete Meissner effect until they reach a single critical magnetic field (Hc), at which point they abruptly stop being superconductive. These are often pure metals.
- Type II superconductors have two critical fields (Hc1 and Hc2). They completely repel the magnetic field up to Hc1. Between Hc1 and Hc2, they enter a mixed state where the magnetic field partially penetrates through specific points called flux vortices, while the rest of the material remains superconducting. They are more useful for creating high-field magnets.
5. Are superconducting magnets considered permanent magnets or electromagnets?
Superconducting magnets are a special type of electromagnet. They function because an electric current, once initiated in a superconducting wire, flows indefinitely without any resistance or power loss. This persistent current generates an incredibly strong and stable magnetic field. Unlike a permanent magnet, this field can be turned off by simply warming the superconductor above its critical temperature.
6. What happens to superconductivity if the electric current in a wire is too high?
According to Silsbee's rule, if the electric current flowing through a superconducting wire becomes too large, it can destroy the superconductivity. This happens because the current itself generates a magnetic field around the wire. If this self-generated field exceeds the material's critical magnetic field, the wire reverts to its normal, resistive state.
7. What are some real-world applications that depend on the magnetic properties of superconductors?
The unique magnetic properties of superconductors are essential for several advanced technologies:
- MRI Machines: Used in hospitals for detailed medical imaging, they rely on powerful and stable magnetic fields from superconducting magnets.
- Maglev Trains: These trains use magnetic levitation, enabled by superconductors, to float above the track, eliminating friction and allowing for very high speeds.
- Particle Accelerators: Facilities like CERN use strong superconducting magnets to bend and focus beams of high-energy particles.
8. What is meant by 'magnetic flux quantization' in a superconductor?
Magnetic flux quantization is a quantum mechanical effect observed in superconducting rings. It means that the magnetic flux (the measure of the total magnetic field passing through the ring) cannot have just any value. Instead, it can only exist in discrete, separate packets or multiples of a fundamental unit called the magnetic flux quantum. This is a direct result of the wave-like nature of electrons in the superconducting state.
