Prologue to Single Molecular Magnet

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Prologue to Single Molecular Magnet Nirmal Ghimire March 16, 2010 In Class Presentation Solid State Physics II Instructor: Elbio Dagotto Department of Physics and Astronomy University of Tennessee at Knoxville

Introduction Quantum Tunneling and Magnetic Relaxation Mn12ac and Fe8 as SMM Conclusion Outline

Introduction External attractive field Arrangement of electronic turn is the root beginning of attraction Traditional attractive materials: Array of inorganic particles made out of transitional metal or lanthanide In 1993 attraction was seen in another sort of material: natural atomic bunch containing transitional metal particles (V, Co, Fe, Ni, Mn ) Magnetism Retained for a few days Magnetized Single Molecular Magnet (SMM) (Gatteschi and Sessoli, Angew. Chem 2003)

Introduction What is fascinating about SMM? Material science perspective Quantum Tunneling Represent the time when established and quantum world meet Application Quantum Computation

Outline Introduction Quantum Tunneling and Magnetic Relaxation Mn12ac and Fe8 as SMM Conclusion

Quantum Tunneling Macroscopic question in one of the two wells No connection between the states No burrowing Quantum protest in the well Wave capacity of question in one well stretches out to the next Quantum burrowing Overlapping of the wave work expels the decline and offers ascend to burrow part

Quantum Tunneling likelihood relies on upon: Tunnel part Barrier tallness Smaller the proportion between the two littler the likelihood of watching burrowing Also relies on upon the collaboration of the molecule with condition Strong Coupling : Localization Intermediate Coupling : Incoherent Tunneling Weak Coupling: Coherent Tunneling

Quantum Tunneling How to compose the Hamiltonian? Two proportionate wells : Unperturbed part (H o ) Wave work collaboration : Perturbation (H 1 ) Coupling between the molecule and condition : Another bother (H 2 ) H = H o +H 1 +H 2 These Hamiltonians rely on upon the framework into thought

Magnetic Relaxation in Large Spin System of Interest-SMM described by: Large Spin ( e.g S =10) Negative anisotropy vitality H O = part because of precious stone field + outside attractive field The marvel of returning of the framework to balance is known as attractive unwinding . (Gatteschi and Sessoli, Angew. Chem 2003)

Magnetic Relaxation in Large Spin System There are three routes in which attractive unwinding can happen: Thermal unwinding Thermally (phonon) helped burrowing Ground state burrowing (J. v. Slageren )

Magnetic Relaxation in Large Spin System In Zero Field , without annoyance, the vitality eigenstate of the framework are immaculate M S states and subsequently burrowing is impractical (J. v. Slageren ) For burrowing, an annoyance Hamiltonian is required. Physically it can be a bending along xy plane called transverse anisotropy An advantageous shape is:

Magnetic Relaxation in Large Spin System The Hamiltonian now gets to be: + H 1 does not drive with H o H is admixture of states H 1 blends levels of S =M and S = M ± 2 The decadence is evacuated because of passage part (J. v. Slageren )

Magnetic Relaxation in Large Spin System In Magnetic field Magnetic field along the simple pivot expels the decline in ± M S However, there happens resounding burrowing under the condition: Hz(n) = nD '; D' = , n =0, 1, 2,… - 9 10 (J. v. Slageren )

Magnetic Relaxation in Large Spin System When attractive field is connected, the vitality levels of the turn microstates change At certain level, these vitality levels cross The annoyance as transverse anisotropy couples the states and burrowing of polarization happens Magnetization unwinding relates to the precarious bit of the circles in Hysteresis circle (J. v. Slageren )

Outline Introduction Quantum Tunneling and Magnetic Relaxation Mn 1 2ac and Fe8 as SMM Conclusion

Mn 1 2ac as Single Molecular Magnet (Hellman Lab Home) (B. Barbara et al., 1999) Mn12ac = [Mn 12 O 12 (CH 3 COO) 16 (H 2 O) 4 ].2CH 3 CHOO.4H 2 0 8 Mn with s=2 (up) 4 Mn with s=3/2 (down) Antiferromagnetic requesting: S =8×2 – 4×3/2 = 10

Mn 1 2ac as Single Molecular Magnet Overall antiferromagnetic coupling is acknowledged from temperature dependance of  m T ( succesptibility item) Value of  m T at room temperature is littler than anticipated for uncoupled twists showed antiferromagnetic coupling Maximumum  m T saw at low temperature (55.6 emu mol - 1 K) is near the incentive for turn S = 10 19.4 emu mol - 1 K(observed) (Gatteschi and Sessoli, Angew. Chem 2003) 31.5 emu mol - 1 K (expected for uncoupled twists)

Mn 1 2ac as Single Molecular Magnet Evidence for attractive anisotropy along simple pivot originates from single precious stone charge The way that the parallel polarization (to the tetragonal hub) soaks considerably more quickly than the opposite charge shows solid anisotropy (Gatteschi and Sessoli, Angew. Chem 2003)

Mn 1 2ac as Single Molecular Magnet Hysteresis circle indicates irregular stairs underneath blocking temperature In level segment unwinding time is significantly bigger than the measuring time scale In the lofty part of the circle unwinding time is of the request of the measuring time scale The circles demonstrate steps related with the quantum burrowing (B. Barbara et al., 1999)

Mn12ac as Single Molecular Magnet Final evidence of quantum burrowing is related with temperature freedom of unwinding time For Mn12ac beneath 2K unwinding time turns out to be tentatively long and consequently dependable estimation gets to be distinctly incomprehensible (Sessoli et al., 1993)

Fe8 as Single Molecular Magnet (Gatteschi and Sessoli, Angew. Chem 2003) (Pulsed EPR) Fe8 = [Fe 8 O 2 (OH 12 (tacn) 6 Br 8 ].(tacn = 1,4,7 –triaza-cyclonane) 6 Fe with s=5/2 (up turn) 2 Fe with s=5/2 (down turn) Antiferromagnetic requesting: S =6×5/2 – 2×5/2 = 10

Fe8 as Single Molecular Magnet Relaxation time gets to be temperature autonomous underneath 400 mK This affirms the nearness of immaculate quantum burrowing As in Mn 1 2 air conditioning, hysteresis demonstrates equidistant charge bounced As with the unwinding time, hysteresis gets to be temperature free beneath 350 mK (Gatteschi and Sessoli, Angew. Chem 2003)

Other Single Molecular Magnets There are numerous different atoms demonstrating the conduct of SMM Some are Fe4, V4, CrM6, Ni 1 2, Mn 1 0 It has been understood that size of the group is not critical for the conduct of SMM The imperative elements are ground state turn S and attractive anisotropy All the other SMM are accounted for to indicate moderate unwinding at temperature lower than Mn 1 2ac

Outline Introduction Quantum Tunneling and Magnetic Relaxation Mn 1 2ac and Fe8 as SMM Conclusion

Conclusion SMMs have opened a road for the investigation of physical marvels at the interface amongst quantum and established world SMM give mark of quantum mechanical conduct in the naturally visible framework They bear the capability of use in future quantum PCs Despite the different effective trial systems, a perfect hypothesis is yet to be produced

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