rare-earth nitride films
DESCRIPTION
Rare-earth nitride films. Electronic structure of SmN, DyN and GdN. Motivation. Localized 4f electrons and delocalized band electrons - a frontier for theory Numerous theoretical predictions Half metals? No consensus! Very little experimental data. - PowerPoint PPT PresentationTRANSCRIPT
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MacDiarmid Institute for Advanced Materials and NanotechnologyVictoria University of Wellington
Andrew Preston ([email protected])
Wellington, New Zealand
Electronic structure of SmN, DyN and GdN
Rare-earth nitride films
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Electronic structure of SmN, DyN and GdN
Motivation
• Localized 4f electrons and delocalized band electrons - a frontier for theory– Numerous theoretical predictions
• Half metals?
– No consensus!
• Very little experimental data
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Electronic structure of SmN, DyN and GdN
Experimental investigation of electronic band structure
• Methods– Growth (in presence of N2)
– Resistivity– Magnetisation (SQUID)– XAS/XES (done at BNL)
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Electronic structure of SmN, DyN and GdN
• Ferromagnetic, Tc ~ 68K
• 7µB/Gd saturation magnetisation
Magnetisation… (GdN)
Granville et al, “Semiconducting ground state of GdN thin films” Phys. Rev. B, 73, 235335 (2006)
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Electronic structure of SmN, DyN and GdN
• Shift in the band edge
• But still semiconducting!
…and Resistivity (GdN)
Granville et al, “Semiconducting ground state of GdN thin films” Phys. Rev. B, 73, 235335 (2006)
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Electronic structure of SmN, DyN and GdN
• Semiconducting!
• Ferromagnet (28K)
Resistivity & Magnetisation (DyN)
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Electronic structure of SmN, DyN and GdN
• Previously reported as antiferromagnetic
• Small moment – relatively large errors
• Clear transition ~ 20K
Resistivity & Magnetisation (SmN)
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Electronic structure of SmN, DyN and GdN
• Semiconducting!• Anomaly at transition
temperature
Resistivity & Magnetisation (SmN)
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Electronic structure of SmN, DyN and GdN
X-ray spectroscopy (DyN)• N k-edge, p-projected
empty DOS
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Electronic structure of SmN, DyN and GdN
X-ray spectroscopy (DyN)• Clear evidence of gap
between XES and XAS• Must be careful of core
hole effects
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Electronic structure of SmN, DyN and GdN
X-ray spectroscopy (DyN)• Compare directly with band
structure calculations (in collaboration with Walter Lambrecht)
• Very good agreement!
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Electronic structure of SmN, DyN and GdN
X-ray spectroscopy (SmN)
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Electronic structure of SmN, DyN and GdN
X-ray spectroscopy (SmN)
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Electronic structure of SmN, DyN and GdN
Summary
• Semiconductors!
• Anomaly in resistivity at Tc – a band shift
• X-ray spectroscopy of valence and conduction bands. Theory is getting close!
Preston et al, “Band structure of SmN and DyN”, Phys. Rev. Lett., submitted
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Electronic structure of SmN, DyN and GdN
Acknowledgements
• Ben Ruck, Jianping Zhong, Joe Trodahl– Victoria University of Wellington– The MacDiarmid Institute
• Walter Lambrecht, Paul Larson– Case Western Reserve University
• James Downes– Macquarie University, Sydney
• Kevin Smith– Boston University
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Electronic structure of SmN, DyN and GdN
Extra
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Electronic structure of SmN, DyN and GdN
Overview
• What are they– Rock salt, RE3+ N3-
– Stronly localized 4f electrons with band electrons.– Highly reactive (unstable in atmosphere)
• and why?– Tough on theory - numerous attempts– No consensus!– No experimental data to guide– Half metals?
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Electronic structure of SmN, DyN and GdN
Extra Results – XxS (DyN)
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Electronic structure of SmN, DyN and GdN
Results – XxS (SmN)
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Electronic structure of SmN, DyN and GdN
Methods
• Theoretical– LSDA+U (W.R.L. Lambrecht)– LSD-SIC (Aerts et al)
• No consensus!