Speaker: Masayuki Hagiwara (Center for Advanced High Magnetic Field Science (AHMF), Graduate School of Science, Osaka University, host: Penc Karlo)
Title: High-field magnetism of the honeycomb-lattice Heisenberg antiferromagnet Cu2(pymca)3(ClO4)
Date: Tuesday, 22 October 2024. 10:00
Place: KFKI Campus, Building 1, Connference room
Abstract:
First, I will introduce our high-magnetic-field facilities and experimental apparatus at AHMF center and talk about research subjects briefly. Then, I will move on to the main topic on magnetic properties of the honeycomb-lattice Heisenberg antiferromagnet Cu2(pymca)3(ClO4) in high magnetic fields where pymca is pyrimidine-2-carboxylate. Cu2(pymca)3(ClO4) is a metal complex compound in which Cu2+ ions (S = 1/2) bridged by pymca form a honeycomb lattice [1]. This substance possesses three different Cu-Cu bond lengths. The temperature dependence of its specific heat shows no peak down to 0.6 K, thus providing no evidence for a long-range magnetic order [2]. The magnetic susceptibility shows a broad maximum near 25 K, which is typical of a low-dimensional antiferromagnet [2]. High-field magnetization curve of Cu2(pymca)3(ClO4) up to 70 T at 1.4 K shows almost no magnetization up to approximately 15 T, a 1/3 magnetization plateau around 20 T, and a 2/3 magnetization plateau near 55 T [2]. From the comparison between the experiment and calculation, two of the three antiferromagnetic exchange interactions are nearly equal, and thus the ground state at zero magnetic field is expected to be a hexagonal singlet state [3]. To clarify the origin of this non-magnetic ground state, we measured the magnetization of powder samples of (Cu1-xZnx)2(pymca)3(ClO4), in which Cu2+ ions are substituted by Zn2+ (non-magnetic) ions. The samples doped with Zn2+ ions exhibited larger magnetization than those of non-doped substance (x=0). We calculated the magnetization values by two methods for the hexagonal and the dimer singlet states, one is based on the existence probability of different types of hexagons composed of Cu2+ and Zn2+ and the other is a Monte Carlo method with annealing. We compared the magnetization between experiment and calculation and found that the calculated magnetization for the hexagonal singlet state is close to the experimental one.
[1] K. Sugawara et al., J. Phys. Soc. Jpn. 86, 123302 (2017).
[2] A. Okutani et al., J. Phys. Soc. Jpn. 88, 013703 (2019).
[3] T. Shimokawa et al., Phys. Rev. B 106, 134410 (2022).
