Direct observation of mixing of spin multiplets in an antiferromagnetic molecular nanomagnet by electron paramagnetic resonance

Datta, Saiti; Waldmann, Oliver; Kent, Andrew D.; Milway, Victoria A.; Thompson, L. K.; Hill, Stephen

doi:10.1103/physrevb.76.052407

Cited by 29 publications

(32 citation statements)

References 22 publications

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“…[4] EPR transitions within excited spin states have been reported for another hexanuclear cyclic Fe III complex [5] and for a nonanuclear Mn II complex. [6] In the case of the cyclic Fe III 6 complex the spectra were interpreted by considering single-ion and dipolar and anisotropic exchange terms to the full spin-Hamiltonian of the system that was diagonalised by use of irreducible tensor operator (ITO) techniques coupled to a group theoretical treatment. [5] In the case of the Mn II 9 complex the EPR spectra were modelled by use of an effective lower-dimension spin-Hamiltonian matrix constructed on the basis of a reduced spin model representing the full system.…”

Section: Introductionmentioning

confidence: 99%

EPR Spectroscopy of a Family of Cr^III₇M^II (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

Piligkos

Weihe

Bill³

et al. 2009

Chemistry A European J

110

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Spinning wheels: The presented highly resolved multifrequency continuous wave EPR spectra (e.g., see figure) of the heterooctametalic "wheels" Cr(7)M provide rare examples of high nuclearity polymetallic systems where detailed information on the spin-Hamiltonian parameters of the ground and excited spin states is observed.We present highly resolved multifrequency (X-, K-, Q- and W-band) continous wave EPR spectra of the heterooctametalic "wheels", [(CH(3))(2)NH(2)][Cr(III) (7)M(II)F(8)((CH(3))(3)CCOO)(16)], hereafter Cr(7)M, where M=Cd, Zn, Mn, and Ni. These experimental spectra provide rare examples of high nuclearity polymetallic systems where detailed information on the spin-Hamiltonian parameters of the ground and excited spin states is observed. We interpret the EPR spectra by use of restricted size effective subspaces obtained by the rigorous solution of spin-Hamiltonians of dimension up to 10(5) by use of the Davidson algorithm. We show that transferability of spin-Hamiltonian parameters across complexes of the Cr(7)M family is possible and that the spin-Hamiltonian parameters of Cr(7)M do not have sharply defined values, but are rather distributed around a mean value.

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Section: Introductionmentioning

confidence: 99%

EPR Spectroscopy of a Family of Cr^III₇M^II (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

Piligkos

Weihe

Bill³

et al. 2009

Chemistry A European J

110

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“…with the sublattices A = {1, 3, 5, 7} and B = {2, 4, 6, 8}, and j R = 0.526J R and d R = 0.197D R for the Mn-[3×3] grid.Ĥ ABC was indeed demonstrated to produce highly accurate results, and was found crucial in the analysis of experimental data (Datta et al, 2007;Waldmann, 2005b;Waldmann et al, 2004). The oscillations in the torque signal originate from an interesting quantum-mixing mechanism (Carretta et al, 2003a;Waldmann et al, 2004).…”

Section: "Modified" Antiferromagnetic Molecular Wheelsmentioning

confidence: 99%

“…However, the mixing is usually not strong enough for such EPR transitions to gain sufficient intensity, but through this mechanism the S = 5/2 → S = 7/2 transition could directly be observed in as function of field in a multi-frequency single-crystal EPR experiment (Datta et al, 2007).…”

Section: "Modified" Antiferromagnetic Molecular Wheelsmentioning

confidence: 99%

Magnetic Cluster Excitations

Fürrer

2010

Int. J. Mod. Phys. B

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Magnetic clusters, i.e., assemblies of a finite number (between two or three and several hundred) of interacting spin centers which are magnetically decoupled from their environment, can be found in many materials ranging from inorganic compounds, magnetic molecules, artificial metal structures formed on surfaces to metalloproteins. The magnetic excitation spectra in them are determined by the nature of the spin centers, the nature of the magnetic interactions, and the particular arrangement of the mutual interaction paths between the spin centers. Small clusters of up to four magnetic ions are ideal model systems to examine the fundamental magnetic interactions which are usually dominated by Heisenberg exchange, but often complemented by anisotropic and/or higher-order interactions. In large magnetic clusters which may potentially deal with a dozen or more spin centers, the possibility of novel many-body quantum states and quantum phenomena are in focus. In this review the necessary theoretical concepts and experimental techniques to study the magnetic cluster excitations and the resulting characteristic magnetic properties are introduced, followed by examples of small clusters demonstrating the enormous amount of detailed physical information which can be retrieved. The current understanding of the excitations and their physical interpretation in the molecular nanomagnets which represent large magnetic clusters is then presented, with an own section devoted to the subclass of the singlemolecule magnets which are distinguished by displaying quantum tunneling of the magnetization. Finally, some quantum many-body states are summarized which evolve in magnetic insulators characterized by built-in or field-induced magnetic clusters. The review concludes addressing future perspectives in the field of magnetic cluster excitations.

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“…(2) can give very reliable estimates of J for molecules in which there is considerable S-mixing, i.e. J ~ d ion (see [13][14][15]22,25,45,71] for further details).…”

Section: 3(b) Experimental Consequences Of Weak Coupling and Spin Fmentioning

confidence: 99%

Magnetic quantum tunneling: insights from simple molecule-based magnets

et al. 2010

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This perspectives article takes a broad view of the current understanding of magnetic bistability and magnetic quantum tunneling in single-molecule magnets (SMMs), focusing on three families of relatively simple, low-nuclearity transition metal clusters: spin S = 4 II 4 Ni , III 3 Mn (S = 2 and 6) and III 6 Mn (S = 4 and 12). The Mn III complexes are related by the fact that they contain triangular III 3 Mn units in which the exchange may be switched from antiferromagnetic to ferromagnetic without significantly altering the coordination around the Mn III centers, thereby leaving the single-ion physics more-or-less unaltered. This allows for a detailed and systematic study of the way in which the individual-ion anisotropies project onto the molecular spin ground state in otherwise identical low-and high-spin molecules, thus providing unique insights into the key factors that control the quantum dynamics of SMMs, namely: (i) the height of the kinetic barrier to magnetization relaxation; and (ii) the transverse interactions that cause tunneling through this barrier. Numerical calculations are supported by an unprecedented experimental data set (17 different compounds), including very detailed spectroscopic information obtained from high-frequency electron paramagnetic resonance and low-temperature hysteresis measurements. Comparisons are made between the giant spin and multi-spin phenomenologies. The giant spin approach assumes the ground state spin, S, to be exact, enabling implementation of simple anisotropy projection techniques. This methodology provides a basic understanding of the concept of anisotropy dilution whereby the cluster anisotropy decreases as the total spin increases, resulting in a barrier that depends weakly on S. This partly explains why the record barrier for a SMM (86 K for Mn 6 ) has barely increased in the 15 years since the first studies of Mn 12 -acetate, and why the tiny Mn 3 molecule can have a barrier approaching 60% of this record. Ultimately, the giant spin approach fails to capture all of the key physics, although it works remarkably well for the purely ferromagnetic cases. Nevertheless, diagonalization of the multi-spin Hamiltonian matrix is necessary in order to fully capture the interplay between exchange and local anisotropy, and the resultant spin-state mixing which ultimately gives rise to the tunneling matrix elements in the high symmetry SMMs (ferromagnetic Mn 3 and Ni 4 ). The simplicity (low-nuclearity, high-symmetry, weak disorder, etc..) of the molecules highlighted in this study proves to be of crucial importance. Not only that, these simple molecules may be considered among the best SMMs: Mn 6 possesses the record anisotropy barrier, and Mn 3 is the first SMM to exhibit quantum tunneling selection rules that reflect the intrinsic symmetry of the molecule.

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Direct observation of mixing of spin multiplets in an antiferromagnetic molecular nanomagnet by electron paramagnetic resonance

Cited by 29 publications

References 22 publications

EPR Spectroscopy of a Family of Cr^III₇M^II (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

EPR Spectroscopy of a Family of Cr^III₇M^II (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

Magnetic Cluster Excitations

Magnetic quantum tunneling: insights from simple molecule-based magnets

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Direct observation of mixing of spin multiplets in an antiferromagnetic molecular nanomagnet by electron paramagnetic resonance

Cited by 29 publications

References 22 publications

EPR Spectroscopy of a Family of CrIII7MII (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

EPR Spectroscopy of a Family of CrIII7MII (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

Magnetic Cluster Excitations

Magnetic quantum tunneling: insights from simple molecule-based magnets

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Resources

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EPR Spectroscopy of a Family of Cr^III₇M^II (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

EPR Spectroscopy of a Family of Cr^III₇M^II (M = Cd, Zn, Mn, Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States