Related Experiment Video
Updated: Jun 21, 2026
11:33
All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics
Published on: January 19, 2018
Magnetic quantum tunneling: key insights from multi-dimensional high-field EPR
J Lawrence1, E-C Yang, D N Hendrickson
1Department of Physics, University of Arizona, Tucson, Arizona 85721, USA.
Physical Chemistry Chemical Physics : PCCP
|July 30, 2009
Summary
High-field/frequency electron paramagnetic resonance (HFEPR) reveals fast magnetic quantum tunneling in a single-molecule magnet (SMM) due to spin mixing. This spin mixing is crucial for understanding quantum dynamics in SMMs.
Area of Science:
- Quantum physics
- Materials science
- Spectroscopy
Background:
- Single-molecule magnets (SMMs) are molecules exhibiting slow relaxation of magnetization.
- Understanding the quantum dynamics of SMMs is key to developing quantum technologies.
- The tetranuclear nickel(II) complex [Ni(hmp)(dmb)Cl](4) is a high-spin (S=4) SMM.
Purpose of the Study:
- To investigate the magnetic quantum tunneling and spin dynamics in the S=4 SMM [Ni(hmp)(dmb)Cl](4).
- To determine the magnetic exchange interactions and zero-field splitting parameters.
- To elucidate the role of spin mixing in the quantum behavior of SMMs.
Main Methods:
- Multi-dimensional high-field/frequency electron paramagnetic resonance (HFEPR) spectroscopy.
- Variable temperature and variable field HFEPR measurements on single crystals.
- Analysis within a rigid spin approximation and perturbation theory.
Main Results:
- Observed four-fold anisotropy attributed to fourth-order transverse zero-field splitting (ZFS).
- Identified a significant tunnel splitting (12 MHz) arising from ZFS-induced mixing of ground states.
- Determined the Heisenberg exchange constant (J = -6.0 cm(-1)) and characterized ZFS in excited states.
Conclusions:
- The fast magnetic quantum tunneling in this SMM is explained by ZFS-induced spin mixing.
- Higher-order processes involving spin mixing between ground and excited states are crucial for the S=4 anisotropy.
- Spin mixing plays a significant role in the low-temperature quantum dynamics of many SMMs.
Related Concept Videos
01:17Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
01:03Atomic Nuclei: Nuclear Spin State Overview
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
01:05Atomic Nuclei: Magnetic Resonance
The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
01:14NMR Spectrometers: Resolution and Error Correction
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
01:08NMR Spectroscopy: Spin–Spin Coupling
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
01:27π Electron Effects on Chemical Shift: Overview
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...