Exploring new quantum states of matter in high magnetic fields is one of the central topics in condensed matter physics. In fact, novel field-induced phases, such as spin-lattice-coupled magnetization plateaus in frustrated spin systems [1], have been extensively investigated to this date. Neutron scattering is one of the most powerful techniques to study magnetic materials because it can probe Fourier-transformed time-space correlation functions of magnetic moments; specifically magnetic structures are determined by the elastic scattering and magnons are measured by the inelastic scatterings. However, the highest magnetic field for neutron scattering instruments is limited to approximately 15 T even for state-of-the-art superconducting magnets.

To enhance the capability of high-field neutron scattering, we recently developed a long-pulsed magnet for time-of-flight (TOF) neutron diffraction measurements [2]. Figure 1 shows a typical temporal profile of the long-pulsed magnetic field. The full-width at half-maximum of the field pulse exceeds 100 ms, which is much longer than the timescale for TOF neutron diffraction measurements. Specifically, the temporal pulse width of a polychromatic neutron pulse, which normally contains wavelengths ranging from 0.5 to 5 Å, will reach approximately 10 ms after flying a typical source-to-sample distance of the existing neutron diffractometers. The pulse width of our long-pulsed magnet is sufficiently longer than this timescale, and therefore all the wavelengths included in a polychromatic neutron pulse can satisfy the high-field condition. In other words, our long-pulsed magnetic field can be regarded as a quasistatic magnetic field for a neutron pulse.

We performed TOF neutron diffraction measurements on a frustrated triangular lattice magnet CuFeO₂ with this long-pulsed magnet at the small and wide-angle neutron diffractometer TAIKAN in the Materials and Life-science experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). The application of the pulsed magnetic field was synchronized with the pulsed neutron beam and repeated about 100 times. As a result, we obtained neutron diffraction intensity maps with varying magnetic field. Figure 2 shows the typical intensity maps at selected magnetic fields. We successfully observed magnetic phase transition from the four-sublattice antiferromagnetic state with the magnetic modulation wavevector of $q = (1/4, 1/4, 0)$ to the 1/5-magnetization plateau phase with $q = (1/5, 1/5, 0)$ [2].

We note that the combination of short pulsed-magnetic fields and a pulsed neutron beam has been already established in previous studies [3]. The advantage of our long-pulsed magnetic field is that we can utilize much wider wavelength range in high magnetic fields as compared to the short-pulsed magnet. Although the highest magnetic field for our setup is still below 15 T, we are going to improve the magnet to generate magnetic fields more than 20 T in the future.

References

• [1] H. Ueda et al., Phys. Rev. Lett. 94, 047202 (2005).
• [2] T. Nakajima et al., Phys Rev. Res. 6, 023109 (2024).
• [3] H. Nojiri et al., Phys. Rev. Lett. 106, 237202 (2011).

Authors

• T. Nakajima, M. Watanabe^a, Y. Inamura^a, K. Matsui, T. Kanda, T. Nomoto, K. Ohishi^b, Y. Kawamura^b, H. Saito, H. Tamatsukuria, N. Terada^c, and  Y. Kohama
• ^aJ-PARC center/JAEA
• ^bCROSS
• ^cNIMS