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2018 NNCI REU Convocation RTNN – Raleigh, NC
Novel Structures and Magnetism in Nanomagnets
Hiroaki KomuroDepartment of Cardiovascular Physiology, Tokyo Medical and
Dental University , JapanPI: Prof. David J. Sellmyer
Mentor: Dr. Balamurugan Balasubramanian, Rabindra PahariDepartment of Physics and Astronomy, University of Nebraska
and Nebraska Center for Materials and Nanoscience
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Outline
1. Introduction
2.Experiment
3. Conclusion
2018 NNCI REU Convocation RTNN – Raleigh, NC
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Cluster-deposition method
He + Ar
Water out
Water in
DC Magnetron Sputtering
Gas-aggregation Chamber
RF Magnetron Sputtering
Carbon
Deposition Chamber
Substrate
Rotatable holder
CoSi
Plasma
Co
Si
• Nanoparticle• Narrow size-distribution
2018 NNCI REU Convocation RTNN – Raleigh, NC
Advantage Application• High-density magnetic recording• Spintronic devices• Ultra-strong permanent magnets
To learn how the magnetic nanoparticles are made and characterized. Objective
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CoSi Skyrmion
(a) Paramagnetism
(b) Ferromagnetism
(C) Antiferromagnetism
(d) Ferrimagnetism
2018 NNCI REU Convocation RTNN – Raleigh, NC
Schematic representations of magnetic dipole arrangements in (a), (b), (c), (d), and (e)
Skyrmion → the non-centrosymmetric B20 cubic structure, such as MnSi, and FeSi
Magnetic skyrmion is a topologically stable particle-like spin configuration
(e) Skyrmion
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CoSi conditioons
Parameter control
• Flow rate• Gas-aggregation distance• Sputtering Power
2018 NNCI REU Convocation RTNN – Raleigh, NC
He + Ar
Water out
Water in
DC Magnetron Sputtering
Gas-aggregation Chamber RF Magnetron
Sputtering
Carbon
Deposition Chamber
Substrate
Rotatable holder
CoSi
Plasma
Co
Si
Sample Sputtering power (W)
Flow rate Ar (sccm)
Flow rateHe (sccm)
Diameter (cm)
Rate (Å/s) Substrate/Time
Charateriz-ation
Sample1 200 400 100 13 5.0 Si/10 min TEM
Sample2 200 400 100 13 2.0 C coated Cu grid/10 sec
SQUID
Sample3 200 400 100 13 2.0 Si/20 sec MFM
This work condition
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TEM micrograph
HRTEM image
2018 NNCI REU Convocation RTNN – Raleigh, NC
Low resolution TEM Image and particle size histogram
Single crystalline particleHigh degree of atomic ordering
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SQUID measurement
2018 NNCI REU Convocation RTNN – Raleigh, NC
Msaturation = 132 emu/cc, 55 emu/cc at 10K and 300K respectively
H =1 kOe
Ferromagnetic, Tc> 300 K
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Analysis1
2018 NNCI REU Convocation RTNN – Raleigh, NC
HRTEM image of nanoparticle Fast Fourier Transform of HRTEM image showing cubic B20 structure.
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Analysis2
2018 NNCI REU Convocation RTNN – Raleigh, NC
Ms = 132 emu/cc, 55 emu/cc at 10K and 300K respectively (SQUID)1 emu = 10-3 J/T, 1 µB = 9.274 × 10-24
J/T In case of 10 KMs = 132 × 88 × 10-24 emu /unit cellMs = 132 × 88 × 10-24 × 10-3 J/TMs = (132 × 88 × 10-24 × 10-3 )/9.27 × 10-24 µBMs = 1.25 µB/ unit cell
Ms = 1.25/4 = 0.31 µB/Co at 10 KMs = 0.52/4 = 0.13 µB/Co at 300 K
a = 4.45 ÅV = 88 Å3 = 88 × 10-24 cm3
No of atoms = 4 Co + 4 Si
Cubic B20 structure
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Conclusions
2018 NNCI REU Convocation RTNN – Raleigh, NC
CoSi nanoparticles were fabricated using cluster-deposition
method.
TEM studies show that the CoSi nanoparticles exhibit an
average size of 11.6 nm and form B20 cubic structure.
Magnetic measurements show that the CoSi nanoparticles
is ferromagnetic with a Curie temperature above 300K.
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Acknowledgements
2018 NNCI REU Convocation RTNN – Raleigh, NC
• Prof. D.J. Sellmyer• All group members • Terese Janovec
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Thank You
2018 NNCI REU Convocation RTNN – Raleigh, NC
