Studying the Magnetic Properties of Helium-3
In joint experimental-theoretical research published in Nature, physicists at the Heidelberg Max Planck Institute for Nuclear Physics (MPIK), together with collaborators from RIKEN, Japan, investigated the magnetic properties of the isotope helium-3. For the first time, the electronic and nuclear g-factors of the 3He+ ion were measured straightly with a relative accuracy of 10– 10.
The electron-nucleus magnetic cooperation (zero-field hyperfine splitting) was gauged with an accuracy boosted by two orders of magnitude. The g-factor of the bare 3He core was defined through an accurate calculation of the electronic shielding. The outcomes compose the first straight calibration for 3He nuclear magnetic resonance (NMR) probes.
The exact knowledge of the magnetic properties of matter on an atomic/nuclear level is of great importance for fundamental physics and applications like Nuclear Magnetic Resonance (NMR) probes. Charged particles with an inherent angular momentum (spin) operate like a little magnetic needle.
The proportionality of magnetic moment (strength of the electromagnetic field) and spin is offered by the alleged g-factor, which is a property of the specific particle and its environment. An atomic or nuclear angular momentum is quantized; specifically, the spin of the electron (even for the core) in 3He can be orientated either parallel or antiparallel to an external magnetic field.
The magnetic interaction of 3He is threefold (Fig. 1): In an outside magnetic field, the magnetic moment guidance of the electron/nucleus can be parallel or antiparallel to the field lines. Additionally, there is the magnetic interaction between electron and nucleus (supposed hyperfine splitting). This triggers overall four energy levels relying on the electronic and nuclear spin guidance.
Transitions between them (matching to a spin-flip) can be resonantly stimulated by microwave radiation. This allows for very accurate measurement of the resonance frequencies, where the g-factors and the hyperfine splitting for a provided magnetic field can be directly deduced.
For the experiment, the scientists of the division of Klaus Blaum at MPIK, along with cooperators from the University of Mainz and RIKEN (Tokyo, Japan), used a single-ion Penning trap (Fig. 2) to gauge the change frequencies between the hyperfine states and concurrently the magnetic field, using the precise determination of the cyclotron frequency of the trapped ion.
Antonia Schneider, the first author of the article, describes the setup of the trap: “It is put inside a 5.7 Tesla superconducting magnet and composed of two components: an accuracy trap for the mensuration of the ion frequencies and the interaction with the microwave radiation and an analysis trap to define the hyperfine state“.
For each switch, the spin-flip rate gets to a maximum at resonance. The g-factors and the zero-field hyperfine splitting are then extracted from the evaluation of the resonance curves. The new experimental configuration improves the precision for the g-factors by a factor of 10 to the level of 10– 10.
“In order to draw out the g-factor of the bare nucleus in 3He2+ from the gauged nuclear g-factor in 3He+, one needs to take into account the diamagnetic shielding of the electron, i.e. its magnetic reaction to the exterior field,” explains Bastian Sikora from the division of Christoph H. Keitel at MPIK.
The theoreticians defined the shielding factor with high precision using very accurate quantum electrodynamic (QED) calculations. They also determined the bound electron g-factor for 3He+ and the zero-field hyperfine splitting inside the theoretical framework.
All theoretical and experimental outcomes are consistent within the matching precision, which has been enhanced for the experimental zero-field hyperfine splitting by two orders of magnitude. The latter was utilized to extract a nuclear parameter (Zemach radius) featuring the nuclear charge and magnetization distribution.
In the future, the researchers prepare to enhance the measurements by decreasing the magnetic inhomogeneity of the accuracy trap and more precise magnetic field measurements. The new measurement technique can also be applied to determine the nuclear magnetic moment of other hydrogen-like ions.
The following action is a straight measurement of the magnetic moment of the bare 3He nucleus in a Penning trap with a relative accuracy on the order of 1 ppb or better by applying sympathetic laser cooling.
More information:
A. Schneider et al, Direct measurement of the 3He+ magnetic moments, Nature (2022). DOI: 10.1038/s41586-022-04761-7
Read the original article on PHYS.
