J. C. Lashley

Critical examination of heat capacity measurements made on a Quantum Design physical property measurement system

Abstract We examine the operation and performance of an automated heat-capacity measurement system manufactured by Quantum Design (QD). QD’s physical properties measurement system (PPMS) employs a thermal-relaxation calorimeter that operates in the temperature range of 1.8–395 K. The accuracy of the PPMS specific-heat data is determined here by comparing data measured on copper and synthetic sapphire samples with standard literature values. The system exhibits an overall accuracy of better than 1% for temperatures between 100 and 300 K, while the accuracy diminishes at lower temperatures. These data confirm that the system operates within the ±5% accuracy specified by QD. Measurements on gold samples with masses of 4.5 and 88 mg indicate that accuracy of ±3% or better can be achieved below 4 K by using samples with heat capacities that are half or greater than the calorimeter addenda heat capacity. The ability of a PPMS calorimeter to accurately measure sharp features in Cp(T) near phase transitions is determined by measuring the specific heat in the vicinity of the first-order antiferromagnetic transition in Sm2IrIn8 (T0=14 K) and the second-order hidden order (HO) transition in URu2Si2 (TN=17 K). While the PPMS measures Cp(T) near the second-order transition accurately, it is unable to do so in the vicinity of the first-order transition. We show that the specific heat near a first-order transition can be determined from the PPMS-measured decay curves by using an alternate analytical approach. This correction is required because the latent heat liberated/absorbed at the transition results in temperature–decay curves that cannot be described by a single relaxation time constant. Lastly, we test the ability of the PPMS to measure the specific heat of Mg11B2, a superconductor of current interest to many research groups, that has an unusually strong field-dependent specific heat in the mixed state. At the critical temperature the discontinuity in the specific heat is nearly 15% lower than measurements made on the same sample using a semi-adiabatic calorimeter at Lawrence Berkeley National Laboratory.

Inversion-symmetry breaking in the noncollinear magnetic phase of the triangular-lattice antiferromagnet Cu Fe O 2

Magnetoelectric and magnetoelastic phenomena have been investigated on a frustrated triangular antiferromagnetic lattice in

Absence of magnetic moments in plutonium

\mathrm{Cu}\mathrm{Fe}{\mathrm{O}}_{2}

Combined Experimental and Theoretical Investigation of the Premartensitic Transition in Ni2MnGa

. Inversion-symmetry breaking, manifested as a finite electric polarization, was observed in noncollinear (helical) magnetic phases and not in collinear magnetic phases. This result demonstrates that the noncollinear spin structure plays an important role in inducing electric polarization. Based on these results we suggest that frustrated magnets (often favoring noncollinear configurations) are favorable candidates for a new class of magnetoelectric materials.

Band Structure of SnTe Studied by Photoemission Spectroscopy

Many theories published in the last decade propose that either ordered or disordered local moments are present in elemental plutonium at low temperatures. We present new experimental data and review previous experimental results. None of the experiments provide any evidence for ordered or disordered magnetic moments (either static or dynamic) in plutonium at low temperatures, in either the

Anisotropic thermal conductivity in uranium dioxide

\ensuremath{\alpha}

Invar model for δ-phase Pu: thermal expansion, elastic and magnetic properties

or

Tin telluride: a weakly co-elastic metal

\ensuremath{\delta}

Low-temperature field effect in a crystalline organic material

phases. The experiments presented and discussed are magnetic susceptibility, electrical resistivity, nuclear magnetic resonance, specific heat, and both elastic and inelastic neutron scattering. Many recent calculations correctly predict experimentally observed atomic volumes, including that of

Quantum criticality in a uniaxial organic ferroelectric

\ensuremath{\delta}