This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Nano Magnetism”.
1. What happens when the local anisotropy is week for particulate nanomagnets?
a) Magnetization changes gradually
b) Magnetization remains unaffected
c) Magnetization alters rapidly
d) Magnetization gets well aligned
View Answer
Explanation: In case of particulate nanomagnets, if the local anisotropy is strong, the magnetization is well aligned. However, for weak local anisotropy there is a gradual change in the magnetization, which effectively overcomes the direction of local anisotropy.
2. Which of the following statements best describes the skyrmions?
a) The product of circulation and core polarity
b) Heterostructures formed by thick magnetic films and light element materials
c) Singularities of the magnetization field characterized by inhomogenities
d) Localized solitary objects having continuous magnetization rotations
View Answer
Explanation: The non-trivial topographical charges of the 3D magnetic spin textures constitute the skyrmions. They subtend the entire 4π steradians of the spin space which leads to their non-trivial integer topological charge. There has been reports of skyrmions in Bose-Einstein condensates, superconductors and thin magnetic films. They act as truly localized solitary objects with continuous magnetization rotation.
3. The reduction in size of the magnetic materials beyond a 10nm can result in super paramagnetism.
a) True
b) False
View Answer
Explanation: If the size of the nanoparticles is small enough, about 10nm, their magnetization can flip direction under the temperature influence. They are known to show super paramagnetism since they can no longer hold any ferromagnetism at such small size.
4. How can we express the probability of switching of direction of magnetization in magnetic particles?
a) P α exp(VkB/T)
b) P α exp(-VKU/kBT)
c) P α exp(1/VkB)
d) P α exp(-T/VKU)
View Answer
Explanation: The magnetic properties get affected upon the reduction in size of the magnetic particles. Below a certain critical size the remanent magnetization is no longer fixed in direction by anisotropy, but can be flipped by thermal energy. The probability of this switching is;
P α exp(-VKU/kBT)
where KU is the local uniaxial anisotropy in the grain volume V, kB is Boltzmann’s constant while T is the temperature.
5. Skyrmions fail to act as localized mobile data for spintronic applications.
a) True
b) False
View Answer
Explanation: Skyrmions have a size of about 10-100nm at room temperature. These skyrmions can act as localized mobile data for spintronic applications because of their small size, topological protection and highly non-collinear spin texture.
6. Which of the following is not a property of strong permanent magnets?
a) High coercivity
b) Low remanence
c) High magnetic field
d) Low mass
View Answer
Explanation: A good permanent magnet has a high remanence (Mr/Ms close to 1), high coercive field, a high Curie temperature, high magnetic field with lower mass. They are also stable against the influences which might demagnetize them.
7. What is the expression for mean anisotropy fluctuations of the grains of particulate nanomagnets?
a) <K> = √(A/K1)
b) <K> = (D√N)/(K1)3/2
c) <K> = Lex/√N
d) <K> = K1(D/Lex)3/2
View Answer
Explanation: The mean anisotropy fluctuation amplitude of the grains is given by;
<K> = K1 (D/Lex)3/2
where D is the grain size with each having anisotropy constant K1 and exchange length Lex.
8. Which of the following properties of the 3D magnetic spin texture have led to their application oriented research?
a) Lower susceptibility to heat currents and magnetic excitations
b) Particle – like properties and lower stability
c) Enhanced stability and higher susceptibility to spin currents
d) Wave – like properties and magnonic excitations
View Answer
Explanation: 3D magnetic spin textures with topological charges possess great stability under external perturbations against transitions into trivial states. Their exceptional stability, particle like properties, high susceptibility to heat, electric and spin currents and magnetic excitons have led to their application-oriented research.
9. Columnar films or nanowires are examples of what kind of nanomagnets?
a) Particulate nanomagnets
b) Hard nanomagnets
c) Geometrical nanomagnets
d) Layered nanomagnets
View Answer
Explanation: Nanomagnets maybe broadly classified into –i) layered nanomagnets: nanometer thick films or multilayer on a supporting substrate; ii) Geometrical nanomagnets: needle – shaped particles or columnar nanowires; (iii) Particulate nanomagnets: granular solids with one or more phases are magnetic, quasi – granular films, nanograined layers on columnar films.
10. How can the skyrmions be stabilized at room temperature?
a) Reducing the thickness of film of the transition metals used
b) Displacing soliton orthogonally to the substrate plane in magnetic superlattices
c) Extending the magnetic data mobility to the vertical direction
d) Providing the interlayer exchange interaction
View Answer
Explanation: The stabilization of the skyrmions can be achieved at room temperature by several ways. First, by increasing the thickness of the transitional metal films. Second, by providing an interlayer exchange interaction. Third, by engineering asymmetric multilayer stacks using heavy element films for additive IDMI at the top and bottom interfaces of the magnetic layer.
Sanfoundry Global Education & Learning Series – Nanotechnology.
To practice all areas of Nanotechnology, here is complete set of 1000+ Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
