Hall Coefficient of Chromium Rafael Jaramillo Thomas Rosenbaum Lab P335 Project

Pure Cr Elemental antiferromagnet below T neel =311 K Spin-density wave aligned along one of crystal axes Spin-flip transition at T SF =123 K image from Isaacs et Al. BCC unit cell

X-Ray Diffraction Results Diffraction images of domains during spin-flip transition; E. D. Isaacs, et Al. (now at Argonne)

Longitudinal Resistivity/ Hall Coefficient Hall coefficient is more sensitive to the T Neel transition than the longitudinal resistivity (see Rosenbaum, et Al.) Sensitivity of the Hall coefficient to the spin-flip transition is unknown Objective: make detailed measurements of R H = (ne) -1 near T SF and T neel –Correlate Hall data near transitions with diffraction data

Experimental Setup Field, temperature controlled by liquid He machine –Magnetic Property Measurement System (MPMS), by Quantum Design Longitudinal resistance, Hall measurements taken with AC resistance bridge, recorded by MPMS software H field longitudinal voltage leads longitudinal current leads Hall voltage leads

Next Steps Magnetoresistance measurements as function of temperature Take Hall data with a single- domain sample –Field-cool the Cr sample through T Neel with a strong enough H field, aligned along one of directions –Need a two-axis field

Selected References Arrott and Werner, “First-Order Magnetic Phase Change in Chromium at 38.5 o C”, Phys. Rev. Lett. 14: (1965) P.G. Evans, E.D. Isaacs, et Al., “X-ray microdiffraction images of antiferromagnetic domain evolution in chromium”, Science 295: (2002) E. Fawcett, “Spin-density-wave antiferromagnetism in chromium”, Rev. Mod. Phys. 60: (1988) A. Yeh, T.F. Rosenbaum, et Al. “Quantum phase transition in a common metal”, Nature 419: (2002(

MPMS Machine Liquid He - cooled system; lowest temp 1.9 K (He 4 boils at 4.2 K) 5 Tesla (max) superconducting magnet Sample space in magnet’s bore; maximum sample width is 9mm