User:Luthyc/Single-molecule magnet

Along with raising the blocking temperature, efforts are being made develop SMMs with high energy barriers to prevent fast spin reorientation.

Magnetic Blocking Temperature
Single molecule magnets, or SMMs, can retain their magnetization with no external field acting on them, giving them the capability for information storage. The main constraint for magnetic memory and information storage of SMMs is their blocking temperature, the point at lower temperatures where magnetic moments are “blocked”. The average blocking temperature for SMMs is 4K. At sub-Kelvin temperatures (below the blocking temperature) a SMM Fe4 complex attached to a gold surface was proven to store information through controlled magnetization with the SMM wired to a conducting surface. Dy-metallocenium salts are the most recent SMM to achieve the highest temperature of magnetic hysteresis, greater than that of liquid nitrogen. There is also a correlation between blocking temperature and energy barrier

Performance
(Cpttt=1,2,4‐tri(tert‐butyl)cyclopentadienide)

* indicates parameters from magnetically dilute samples

Applications
Single-molecule magnets have been considered as potential building blocks for quantum computers. A single-molecule magnet is a system of many interacting spins with clearly defined low-lying energy levels. The high symmetry of the single-molecule magnet allows for a simplification of the spins that can be controllable in external magnetic fields. Single-molecule magnets display strong anisotropy, a property which allows a material to assume a variation of properties in different orientations. Anisotropy ensures that a collection of independent spins would be advantageous for quantum computing applications. A large amount of independent spins compared to a singular spin, permits the creation of a larger qubit and therefore a larger faculty of memory. Superposition and interference of the independent spins also allows for further simplification of classical computation algorithms and queries.

Theoretically, quantum computers can overcome the physical limitations presented by classical computers by encoding and decoding quantum states. Single-molecule magnets have been utilized for the Grover algorithm, a quantum search theory. The quantum search problem typically requests for a specific element to be retrieved from an unordered database. Classically the element would be retrieved after N/2 attempts, however a quantum search utilizes superpositions of data in order to retrieve the element, theoretically reducing the search to a single query. Single molecular magnets are considered ideal for this function due to their cluster of independent spins. A study conducted by Leuenberger and Loss, specifically utilized crystals to amplify the moment of the single spin molecule magnets Mn12 and Fe8. Mn12 and Fe8 were both found to be ideal for memory storage with a retrieval time of approximately 10-10 seconds.

Another approach to information storage with SMM Fe4 involves the application of a gate voltage for a state transition from neutral to anionic. Using electrically gated molecular magnets offers the advantage of control over the cluster of spins during a shortened time scale. The electric field can be applied to the SMM using a tunneling microscope tip or a strip-line. The corresponding changes in conductance are unaffected by the magnetic states, proving that information storage could be performed at much higher temperatures than the blocking temperature. The specific mode of information transfer includes DVD to another readable medium, as shown with Mn12 patterned molecules on polymers.

Another application for SMMs is in magnetocaloric refrigerants. A machine learning approach using experimental data has been able to predict novel SMMs that would have large entropy changes. Three hypothetical SMMs are proposed for experimental synthesis:, ,. The main SMM characteristics that contribute to the entropy properties include dimensionality and coordinating ligands.