Quantum matter in high magnetic fields

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A chiral ferromagnetic molecular metal.

J Am Chem Soc 132:27 (2010) 9271-9273

Authors:

José R Galán-Mascarós, Eugenio Coronado, Paul A Goddard, John Singleton, Amalia I Coldea, John D Wallis, Simon J Coles, Antonio Alberola

Abstract:

The first molecular material with the coexistence of ferromagnetism, metal-like conductivity, and chirality has been prepared using an organic/inorganic approach. In this case, a two-dimensional packing of chiral organic radical cations (responsible for both the electrical conductivity and optical activity) was assembled with a layered bimetallic oxalate-based anionic network (responsible for the magnetic properties). Shubnikov-de Haas oscillations confirmed the presence of a Fermi surface even when the transport properties suggested "insulating"-type behavior at very low temperatures.
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Dimensionality-driven spin-flop transition in quasi-one-dimensional PrBa2 Cu4 O8

Physical Review B - Condensed Matter and Materials Physics 81:22 (2010)

Authors:

X Xu, A Carrington, AI Coldea, A Enayati-Rad, A Narduzzo, S Horii, NE Hussey

Abstract:

In the quasi-one-dimensional cuprate PrBa2 Cu4 O 8, the Pr cations order antiferromagnetically at 17 K in zero field. Through a combination of magnetic susceptibility, torque magnetometry, specific heat, and interchain transport measurements, the anisotropic temperature-magnetic-field phase diagram associated with this ordering has been mapped out. A low-temperature spin-flop transition in the Pr sublattice is found to occur at the same magnetic field strength and orientation as a dimensional crossover in the ground state of the metallic-CuO chains. This coincidence suggests that the spin reorientation is driven by a change in the anisotropic Rudermann-Kittel-Kasuya-Yosida interaction induced by a corresponding change in effective dimensionality of the conduction electrons. © 2010 The American Physical Society.
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Evolution of the Fermi surface of BaFe2(As1-xPx){2} on entering the superconducting dome.

Phys Rev Lett 104:5 (2010) 057008

Authors:

H Shishido, AF Bangura, AI Coldea, S Tonegawa, K Hashimoto, S Kasahara, PMC Rourke, H Ikeda, T Terashima, R Settai, Y Onuki, D Vignolles, C Proust, B Vignolle, A McCollam, Y Matsuda, T Shibauchi, A Carrington

Abstract:

Using the de Haas-van Alphen effect we have measured the evolution of the Fermi surface of BaFe2(As1-xPx){2} as a function of isoelectric substitution (As/P) for 0.41
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Interplay between localized and itinerant d electrons in a frustrated metallic antiferromagnet, 2H-AgNiO2

ArXiv 0908.4169 (2009)

Authors:

AI Coldea, A Carrington, R Coldea, L Malone, AF Bangura, MD Johannes, II Mazin, EA Yelland, JG Analytis, JAAJ Perenboom, C Jaudet, D Vignolles, T Sorgel, M Jansen

Abstract:

We report the electronic and magnetic behaviour of the frustrated triangular metallic antiferromagnet 2H-AgNiO2 in high magnetic fields (54 T) using thermodynamic and transport measurements. Here localized d electrons are arranged on an antiferromagnetic triangular lattice nested inside a honeycomb lattice with itinerant d electrons. When the magnetic field is along the easy axis we observe a cascade of field-induced transitions, attributed to the competition between easy-axis anisotropy, geometrical frustration and coupling of the localized and itinerant system. The quantum oscillations data suggest that the Fermi surface is reconstructed by the magnetic order but in high fields magnetic breakdown orbits are possible. The itinerant electrons are extremely sensitive to scattering by spin fluctuations and a significant mass enhancement (~ 3) is found.
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Fermi surface of SrFe2P2 determined by the de Haas-van Alphen effect.

Phys Rev Lett 103:7 (2009) 076401

Authors:

JG Analytis, CMJ Andrew, AI Coldea, A McCollam, J-H Chu, RD McDonald, IR Fisher, A Carrington

Abstract:

We report measurements of the Fermi surface (FS) of the ternary iron-phosphide SrFe2P2 using the de Haas-van Alphen effect. The calculated FS of this compound is very similar to SrFe2As2, the parent compound of the high temperature superconductors. Our data show that the Fermi surface is composed of two electron and two hole sheets in agreement with band-structure calculations. Several of the sheets show strong c-axis warping emphasizing the importance of three dimensionality in the nonmagnetic state of the ternary pnictides. We find that the electron and hole pockets have a different topology, implying that this material does not satisfy a (pi, pi) nesting condition.
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