Ⅲ-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 49 (2016)µSR study of spin dynamics in Cu-based organic-inorganic hybridsystems
E. Suprayoga,∗1,∗2 A. A. Nugroho,∗2 D. Onggo,∗2 and I. Watanabe∗1
The muon-site is a very important parameter tostudy the hyperﬁne interaction between muon andelectrons and to discuss ordered states of electronic
spins in magnetic materials. In the previous report,1)
we have estimated muon-sites in organic-inorganic hybrid materials of (C6 H5 CH2 CH2 NH3 )2 CuCl4 (PEA)and (C2 H5 NH3 )2 CuCl4 (EA) by taking into accountthe minimum electrostatic potential energy based on
the density functional theory (DFT). Accordingly, we
estimated six muon-site candidates in EA and eightcandidates in PEA; nevertheless, only one site was experimentally achieved on both materials with an internal ﬁeld of around 200 G at 4 K.2) A new achievement
for PEA has been obtained at the RIKEN-RAL muon
facilities. The internal ﬁeld of PEA increases by decreasing the temperature with 240 G at 1.5 K. Thisresult can be used to discuss the magnetic interaction
mechanism between magnetic layers in PEA system.
In order to understand the magnetic interaction in
EA and PEA systems and to explain the experimental
results, we performed DFT and dipole ﬁeld calculations by using the HOKUSAI, RIKEN supercomputer.
To begin with, we put a muon at the minimum potential position in a bulk structure of 2 × 2 × 1 supercell
to study the localization of the muon. To obtain theﬁnal stable muon position, we made a self-consistency
test by using the generalized gradient approximation(GGA) and augmented plane wave (APW) pseudopotential methods as implemented in the VASP package.3) During the self-consistency, the muon moved
to the side of CuCl4 octahedral, pushed the nearest
Cu2+ ion and deformed the local crystal structure due
to change in the local potential around the muon, asshown in Fig. 1 and 2.

Fig. 2. Local structure deformation of (C2 H5 NH3 )2 CuCl4(EA) by the injected muon.

In order to conﬁrm our muon-site candidates, wecalculated electronic dipole ﬁelds at the muon position
coming to the magnetic moment of Cu2+ spins. We
assumed the ferromagnetic spin alignment as previously suggested from the susceptibility measurement4)
and calculated electronic dipolar ﬁelds in three diﬀerent orientations along the a-, b-, and c- axes to ﬁnd
the ground-state condition. We also considered otherquantum eﬀects such as the zero-point vibration motion of the muon, the spatial distribution of the magnetic moments, and the deformation of the surrounding
electronic orbital by the injected muon.
Our DFT calculation results on both Cu-hybrid systems show the appearance of magnetic moment distribution of Cl− as well as that of Cu2+ ions. We estimated the size of magnetic moment around 0.5 µB and0.1 µB for Cu2+ and Cl− ions, respectively, to calculate dipole ﬁelds at the muon site. In order to obtain
the accurate muon position, we suggested the supercell calculation to see local deformation of the ionicposition due to injected muon. Finally, by including
those eﬀects, we can compare the experimental resultsof internal ﬁelds at the muon-site in order to determine
the spin structure of Cu-hybrid EA and PEA. Detailed
calculations and further discussion of the magnetic interaction mechanism between magnetic layers on thosehybrids are under way and we expect to obtain the ﬁnal results and conclusions very soon.
References

Fig. 1. Local structure deformation of (C6 H5 CH2 CH2 NH3 )2
CuCl4 (PEA) by the injected muon.
∗1∗2RIKEN Nishina Center
FMIPA, Institut Teknologi Bandung- 221 -1) E. Suprayoga et al.: RIKEN Accell. Prog. Rep. 48, 267(2015).
2) A. A. Nugroho et al.: RIKEN Accell. Prog. Rep. 45,193 (2012).
3) G. Kresse and J. Furthmuller: Phys. Rev. 54, 11169(1996).
4) L. J. De Jongh et al.: Physica 58, 277 (1972).