Biography

Lieh Jeng joined the group in October 1993 after completing his first degree and his Masters in Taiwan. His arrival coincided with the discovery of the rare earth nickel boron carbides, a new class of magnetic superconductors, and so he immediately began working on these materials. Lieh-Jeng graduated in February 1997. Lieh Jeng is currently a Professor in the Physics Department National Cheng Kung University.

Lieh Jeng with Don Paul outside the Physics Department on graduation day.

 

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Summary of Ph.D. thesis

Polycrystalline samples were prepared using an argon arc furnace. Later, single crystal samples were grown using a flux method. The samples were characterised by x-ray diffraction, resistivity and ac susceptibility measurements. An apparatus was constructed to measure the thermopower of the borocarbides other materials between 1.5 K and room temperature. Neutron diffraction measurements were performed at ORNL, USA, Risø in Denmark and at the ILL in France.

The magnetic structures of many R-Ni-B-C (R=rare earth) compounds were determined using neutron diffraction techniques. These compounds include the magnetic superconductors RNi₂B₂ C (R=Dy, Ho, Er and Tm) and the magnetic materials TbNi₂B₂C, HoNiBC and ErNiBC which are not superconductors.

Commensurate magnetic structures are only observed in the compounds HoNi₂B₂C (T<8.5 K), DyNi₂B₂C (T<10 K) HoNiBC (T<10K) and ErNiBC (T<4.5 K). Incommensurate magnetic structure were observed in HoNi₂B₂C (modulated along the a axis (5 <T<7 K) and the c axis (5 < T <8.5 K) directions), ErNi₂B₂ C (modulated along the a axis (T<7 K)), TmNi₂B₂C (modulated along the 110 direction (T<1.5 K)) and TbNi₂B₂C (modulated along the a axis direction (T<15.5K)).

The magnetic structures of some doped HoNi₂B₂C compounds were also investigated due the complex structure of pure HoNi₂B₂C. Ho_0.9Y_0.1 Ni₂B₂C shows a helical structure lying on the ab-plane whilst Ho_0.95La_0.05Ni₂B₂C shows a helical cone magnetic structure (helimagnetic configuration in the ab-plane plus an antiferromagnetic configuration along the c axis).

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Publications resulting from Ph.D. work

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The nature of magnetic ordering in TbNi₂B₂, C.V. Tomy, L. J. Chang, D. M. Paul, C. Ritter, Physica B 230, 872 (1997).

Full Text PDF: Download (210kB)

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Magnetic structure of TmNi₂B₂C, L. J. Chang, C. V. Tomy, D. M^cK. Paul, C. Ritter, Physical Review B-Condensed Matter 54, 9031-9034 (1996).

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Neutron diffraction studies of Ho_1-xY_xNi₂B₂C compounds, L. J. Chang, C. V. Tomy, D. M^cK. Paul, N. H. Andersen, M. Yethiraj, Physica B 224, 119-122 (1996).

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Magnetic order in HoNiBC and ErNiBC, L. J. Chang, C. V. Tomy, D. M. K. Paul, N. H. Andersen, M. Yethiraj, Journal of Physics-Condensed Matter 8 , 2119-2125 (1996).

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Neutron Diffraction From HoNi₂B₂C, C. V. Tomy, L. J. Chang, D.M^cK. Paul, N. H. Andersen, M. Yethiraj, Physica B 213, 139-141 (1995).

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Superconductivity in RNi₂B₂C (R=Rare Earth) Compounds, C. V. Tomy, L. J. Chang, G. Balakrishnan, D. M^cK. Paul, Physica C 235, 2551-2552 (1994).

Write to

Physics Department

National Cheng Kung University

Tainan 701

Taiwan

Contact Details

Telephone
+886 (0)6 2757575 ext. 65224
E-Mail
ljchang at mail dot ncku dot edu dot tw

Thesis Abstract

Neutron diffraction studies of the magnetic structures of R-Ni-B-C compounds

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