Examines the magnetic properties of helium-3

Examines the magnetic properties of helium-3

How magnetic is helium-3? Fig. 1: Schematic view of 3he+ ion external and internal magnetic interactions. Background: microwave radiation. Credit: MPI

In a joint experimental-theoretical study published in Nature, physicists at the Heidelberg Max Planck Institute for Nuclear Physics (MPIK), together with colleagues from RIKEN, Japan, investigated the magnetic properties of the isotope helium-3. For the first time, they have electronic and nuclear g-factors 3he+ ions were measured directly with a relative precision of 10–10. The magnetic interaction between the electron and the nucleus (zero-field hyperfine splitting) was measured with an accuracy that was improved by two orders of magnitude. The g-factor is naked 3The core was determined via a careful calculation of the electronic shielding. The results are the first direct calibration for 3He breaks down nuclear magnetic resonance (NMR).

The exact knowledge of the magnetic properties of matter at the atomic / nuclear level is of great importance for basic physics as well as for applications such as nuclear magnetic resonance (NMR) probes. Charged particles with an inherent momentum (spin) act as a small magnetic needle. The proportionality between magnetic moment (the strength of the magnetic field) and spin is given by the so-called g-factor, which is a property of the specific particle and its environment. An atomic or nuclear momentum is quantized: in particular the spin of the electron (as for the nucleus) in 3He can be oriented either parallel or antiparallel to an external magnetic field.

The magnetic interaction of 3He is threefold (fig. 1): In a external magnetic field, the magnetic moment orientation of the electron / nucleus can be parallel or antiparallel to the field lines. In addition, there is the magnetic interaction between electron and nucleus (so-called hyperfine splitting). This leads to a total of four energy levels depending on the electronic and nuclear spin orientation. Transitions between them (corresponding to a spin-flip) can be resonantly induced by microwave radiation. This enables a very accurate measurement of the resonant frequencies, from which the g-factors as well as the hyperfine division for a given magnetic field can be directly derived.

How magnetic is helium-3? Fig. 2: Photograph and schematic view of the Penning trap for 3he+ measurement of hyperfine structure. Credit: MPI

For the experiment, the researchers in the department of Klaus Blaum at MPIK together with collaborators from the University of Mainz and RIKEN (Tokyo, Japan) used an ion Penning trap (Fig. 2) to measure the transition frequencies between the hyperfine states and at the same time the magnetic field, via careful determination. of the cyclotron frequency of the captured ion.

Antonia Schneider, first author of the article, describes the set-up of the trap: “It is placed inside a 5.7 Tesla superconducting magnet and consists of two parts: a precision trap for measuring ion frequencies and interaction with microwave radiation and an analysis trap for determining the hyperfine state.” For each transition, the spin-flip speed reaches a maximum at resonance. The G-factors and the zero field hyperfine division are then extracted from the analysis of the resonance curves. The new experimental setup improves the precision of the g-factors by a factor of 10 to the level 10–10.

“To extract the g-factor of the naked nucleus in 3he2+ from the measured nuclear g-factor in 3he+one must take into account the electromagnetic shielding of the electron, ie its magnetic response to the outer field “, explains Bastian Sikora from Christoph H. Keitel’s division at MPIK.

Theorists determined the shielding factor with high precision using very accurate quantum electrodynamic (QED) calculations. Within the same theoretical frameworkthey also calculated the g-factor of the bound electron for 3he+ and zero-field hyperfine division. All theoretical and experimental results are consistent within the corresponding accuracy, which has been improved for the experimental zero-field hyperfine division by two orders of magnitude. The latter was used to extract a core parameter (Zemach radius) that characterizes the core charge and excitation distribution.

In the future, researchers plan to improve the measurements by reducing the magnetic inhomogeneity in the precision trap and more accurate magnetic field measurements. The new measurement method can also be used to determine the nuclear magnetic moment for other hydrogen-like ions. A next step is a direct measurement of the mere magnetic moment 3He core in a Penning trap with a relative precision of the order of 1 ppb or better by implementing sympathetic laser cooling.

Solution to the hyper-fine puzzle within reach

More information:
A. Schneider et al, Direct measurement of 3He + magnetic moments, Nature (2022). DOI: 10.1038 / s41586-022-04761-7

Provided by
Max Planck Society

Quote: Examines the magnetic properties of helium-3 (2022, June 8) retrieved June 8, 2022 from https://phys.org/news/2022-06-magnetic-properties-helium-.html

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