Ⅲ-2. Atomic & Solid State Physics (Muon)
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

The eﬀect of particle size on magnetic properties regarding La2 CuO4
nanoparticles
A. E. Putri,∗1,∗2 B. Kurniawan,∗2 and I. Watanabe∗1
The nano size eﬀect is an interesting physical phenomenon because it shows unique properties comparedto those observed in a bulk condition. One example is
the gold (Au). When the particle size of Au was reduced
to be in the nano-scale size, ferromagnetic behavior
was observed, whose origin is still unknown.1) Changes
in magnetic properties due to particle size reductions
were also observed in the La-based high-Tc superconducting oxide, La2−x Srx CuO4 (LSCO).2) Synthesizing
LSCO nanoparticles experiences numerous diﬃculties
regarding the control of defects and impurities.3) Thus,
an investigation to optimize sample preparation is aprerequisite.
The La2 CuO4 (LCO), a parental compound of LSCO
exhibiting antiferromagnetic Mott insulator behavior atTN ≈ 300 K,4) will be investigated considering a nanosize particle. LCO nanoparticle were synthesized using
sol-gel method with lanthanum oxide, La2 O3 (99.99%),
and cooper oxide, CuO (99.99%), as a raw material similar to a previous research.5) Particles size of LCO canbe controlled by varying the sintering temperature at
650◦ C, 700◦ C, 750◦ C, 800◦ C, and 1100◦ C over 6 hours
which produce 43 nm, 54 nm, 70 nm, 90 nm, and 161 nm
particle size, respectively. Rietveld reﬁnement method
is used to analyze the X-ray diﬀractometer (XRD) pattern, which exhibit an orthorhombic crystal structurewith Bmab-space group. Small impurities were detected at the lowest sintering temperature of 650◦ C,
which correspond to approximately 1.3% of La2 O3 coming from the raw material. Because La2 O3 has no magnetic component, the magnetic properties of this sample should not be aﬀected. The LCO particle size (D)estimated using the Debye Scherrer method is express
using the following equation:
D = κλ/β cos θ(1)where κ is the Scherrer constant (0.9), λ is the wavelength of Cu-Kα (1.5406 Å) obtained from XRD measurements, β denotes the full width of half maximum intensity observed from XRD pattern and θ is the Braggs
angle.
The La2 CuO4 is composed of a basic unit of CuO6 octahedron crystal structure, which has been thoroughly
investigated in the past. Changing the particle size ofLCO aﬀects the antiferromagnetic transition temperature (TN ), as shown in Fig 1. Reducing the particle
size of LCO up to 43 nm can decrease the TN down
to 65 K. This nano-size eﬀect was also investigated onmagnetic materials, such as CuO. Accordingly, it wasreported that the Néel temperature, TN , of CuO could∗1∗2

RIKEN Nishina Center
Department of Physics, Universitas Indonesia

Fig. 1. Particle size dependance of the antiferromagnetictransition temperature, determined from the χ measurement at 0.0001 T with zero ﬁeld cooled method using Superconducting Quantum Interference Device (SQUID)
magnetometer MPMS. The insert ﬁgure demonstrates
the temperature dependance of magnetic susceptibility
for sample A.

be reduced from 290 K down to 40 K when CuO particle size was reduced to approximately 5 nm.6) Thosestudies indicated that the magnetic exchange interaction would be aﬀected by the reduction of particle size.
The largest particle size exhibits a superconducting
state below 40 K, which corresponds to the transition
temperature of LSCO doped with 15% strontium.2) The
antiferromagnetic long-range order was suppressed andsuperconductivity occurred owing to the excess oxygen inside the LCO sample,7) which led to the phaseseparation of partial superconductivity. Interestingly,
reducing the particle size of LCO down to nano-size
suppressed the superconductivity behavior below 40 K,
which occurred owing to the excess oxygen. Otherwise,
magnetic susceptibility of LCO nanoparticle below 50 K
can be ﬁt using Curie-Weiss equation, showing that themagnetic free spins increase by decreasing the particle
size.
References
1) Y. Yamamoto et al., Phys. Rev. Lett. 93, 116801 (2004).
2) Y. Yin et al., Phys. Chem. C 117, 3028 (2013).
3) S. Winarsih et al., Mater. Sci. Forum 966, 357 (2019).
4) P. A. Lee, et al., Rev. Mod. Phys. 78 (2006).
5) A. E. Putri et al., Mater. Sci. Forum 1028, 44 (2021).
6) X. G. Zheng et al., Phys. Rev. B 72, 014464 (2005).
7) Y. Okajima et al., Physica C 282–287, 1319 (1997).

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