Hall Coefficient of Chromium

Rafael Jaramillo

Thomas Rosenbaum Lab

P335 Project

Pure Cr

• Elemental antiferromagnet below Tneel=311 K

• Spin-density wave aligned along one of <100> crystal axes

• Spin-flip transition at TSF=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 TNeel 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 RH = (ne)-1 near TSF and Tneel

– 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

TNeel with a strong enough H field, aligned along one of <100> directions

– Need a two-axis field

Selected References

• Arrott and Werner, “First-Order Magnetic Phase Change in Chromium at 38.5oC”, Phys. Rev. Lett. 14: 1022-1024 (1965)

• P.G. Evans, E.D. Isaacs, et Al., “X-ray microdiffraction images of antiferromagnetic domain evolution in chromium”, Science 295: 1042-1045 (2002)

• E. Fawcett, “Spin-density-wave antiferromagnetism in chromium”, Rev. Mod. Phys. 60: 209-283 (1988)

• A. Yeh, T.F. Rosenbaum, et Al. “Quantum phase transition in a common metal”, Nature 419: 459-462 (2002(

MPMS Machine

• Liquid He - cooled system; lowest temp 1.9 K (He4 boils at 4.2 K)

• 5 Tesla (max) superconducting magnet

• Sample space in magnet’s bore; maximum sample width is 9mm