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Abstract:

TmAgGe is an antiferromagnet in which the spins are confined to distorted kagome-like planes at low temperatures. We report angle-dependent measurements of the magnetization M in fields of up to 55 T that show that there are two distinct and separate energy scales present in TmAgGe, each responsible for a set of step-like metamagnetic transitions: weak exchange interactions and strong crystalline-electric-field (CEF) interactions. Simulations of M using a three-dimensional, free-energy minimization technique allow us to specify the physical origin of the metamagnetic transitions in low, in-plane fields. We also show that the transitions observed with the field perpendicular to the kagome planes are associated with the CEF-split multiplet of Tm. © 2007 The American Physical Society.

Abstract:

The interlayer magnetoresistance ρzz of the organic metal κ-(BEDTTTF)2Cu(NCS)2 has been studied in fields B of up to 45 T and at temperatures T from 0.5 K to 50 K. The peak in ρzz seen in exactly in-plane fields, a definitive signature of interlayer coherence, remains to Ts exceeding the Anderson criterion for incoherent transport by a factor ∼ 25. Angle-dependent magnetoresistance oscillations (AMROs) due to Fermi-surface orbits are suppressed by rising T, with a T2dependence suggesting electron-electron scattering. © 2006 IOP Publishing Ltd.

Abstract:

We present results of magnetization and electron paramagnetic resonance experiments on the spin-dimer system BaCu Si2 O6. Evidence indicates that the origin of anisotropic terms in the spin Hamiltonian lies in magnetic dipolar interactions. Axial symmetry breaking is on a very small energy scale of ≤11 mK, confirming Bose-Einstein condensation critical scaling over an extended temperature range in the vicinity of the quantum critical point. © 2006 The American Physical Society.

Abstract:

This article reviews high magnetic field magnetization measurements of the shape memory alloy AuZn. These measurements elucidate the underlying electronic mechanism driving this effect. The application of high magnetic fields (up to 65 T), in combination with exceptional sample purity and light electronic effective masses enables the observation of magnetic quantum oscillations over an unprecedented range of temperatures (up to 100 K); thus the electronic band structure can be tracked across the shape memory phase transition (at T=67 K) and the Fermi surface nesting event driving it identified. © 2006 Elsevier Ltd. All rights reserved.

Abstract:

We describe instrumentation designed to perform millimeter-wave conductivity measurements in pulsed high magnetic fields at low temperatures. The main component of this system is an entirely nonmetallic microwave resonator. The resonator utilizes periodic dielectric arrays (photonic band-gap structures) to confine the radiation, such that the resonant modes have a high Q factor, and the system possesses sufficient sensitivity to measure small samples within the duration of a magnet pulse. As well as measuring the sample conductivity to probe orbital physics in metallic systems, this technique can detect the sample permittivity and permeability allowing measurement of spin physics in insulating systems. We demonstrate the system performance in pulsed magnetic fields with both electron paramagnetic resonance experiments and conductivity measurements of correlated electron systems. © 2006 American Institute of Physics.