ELFT HÍRADÓ

[Szeminárium koordinátor <sem-admin AT szfki.hu>]

SZFI SeminarMasayuki HagiwaraCenter for Advanced High Magnetic Field Science 
(AHMF), Graduate School of Science, Osaka University (host: Penc 
Karlo)High-field magnetism of the honeycomb-lattice Heisenberg 
antiferromagnet Cu2(pymca)3(ClO4) Tuesday, 22 October 2024, 10:00, KFKI 
Campus, Bldg. 1, 2nd floor, Conference RoomFirst, 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). Minden érdeklődőt szívesen látunk! 
- Everyone is welcome to attend.Attila Nagysem-admin AT szfki.hu