arXiv subjects

P. Tong

Publications and source records attributed to P. Tong.

23 records · Page 2Linked to original sources

arXiv2009

The observation of a positive magnetoresistance and close correlation among lattice, spin and charge around TC in antipervoskite SnCMn3

The temperature dependences of magnetization, electrical transport, and thermal transport properties of antiperovskite compound SnCMn3 have been investigated systematically. A positive magnetoresistance (~11%) is observed around the ferrimagnetic-paramagnetic transition (TC ~ 280 K) in the field of 50 kOe, which can be attributed to the field-induced magnetic phase transition. The abnormalities of resistivity, Seebeck coefficient, normal Hall effect and thermal conductivity near TC are suggested to be associated with an abrupt reconstruction of electronic structure. Further, our results indicate an essential interaction among lattice, spin and charge degrees of freedom around TC. Such an interaction among various degrees of freedom associated with sudden phase transition is suggested to be characteristic of Mn-based antiperovskite compounds.

cond-mat.str-el↗

arXiv2009

Reversible room-temperature magnetocaloric effect with large temperature span in antiperovskite compounds Ga1-xCMn3+x (x=0, 0.06, 0.07, and 0.08)

The magnetic and magnetocaloric properties of Ga1-xCMn3+x have been investigated. Reversible magnetocaloric effect (MCE) occurs near the Curie temperature TC. The magnetic entropy change decreases with increasing x, though TC and magnetization increases. Meanwhile, the temperature span of vs. T plot becomes well broadened with x. Due to the competition between the broadening temperature span and decreasing, the relative cooling power (RCP) increases initially, and then decreases with increasing x. The largest RCP (2.1 J/cm3, under 45 kOe) observed when x=0.07 (TC = 296.5 K) is comparable to the contemporary magnetic refrigerant materials. Considering the reversible MCE, inexpensive and innoxious raw materials, our result suggests that Ga1-xCMn3+x can be promising candidate for magnetic refrigeration around room temperature.

cond-mat.str-el↗

arXiv2009

Large magnetic entropy change near room temperature in antipervoskite SnCMn3

We report the observation of large magnetocaloric effect near room temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48 kOe, respectively. These values are close to those of typical magnetocaloric materials. The large magnetocaloric effect is associated with the sharp change of lattice, resistivity and magnetization in the vicinity of TC. Through the measurements of Seebeck coefficient and normal Hall effect, the title system is found to undergo a reconstruction of electronic structure at TC. Considering its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are suggested to be appropriate for pursuing new materials with larger magnetocaloric effect.

cond-mat.str-el↗

arXiv2003

Extraction of Plumes in Turbulent Thermal Convection

We present a scheme to extract information about plumes, a prominent coherent structure in turbulent thermal convection, from simultaneous local velocity and temperature measurements. Using this scheme, we study the temperature dependence of the plume velocity and understand the results using the equations of motion. We further obtain the average local heat flux in the vertical direction at the cell center. Our result shows that heat is not mainly transported through the central region but instead through the regions near the sidewalls of the convection cell.

nlin.CD↗

arXiv2000

Measurements of the instantaneous velocity difference and local velocity with a fiber-optic coupler

New optical arrangements with two single-mode input fibers and a fiber-optic coupler are devised to measure the instantaneous velocity difference and local velocity. The fibers and the coupler are polarization-preserving to guarantee a high signal-to-noise ratio. When the two input fibers are used to collect the scattered light with the same momentum transfer vector but from two spatially separated regions in a flow, the obtained signals interfere when combined via the fiber-optic coupler. The resultant light received by a photomultiplier tube contains a cross-beat frequency proportional to the velocity difference between the two measuring points. If the two input fibers are used to collect the scattered light from a common scattering region but with two different momentum transfer vectors, the resultant light then contains a self-beat frequency proportional to the local velocity at the measuring point. The experiment shows that both the cross-beat and self-beat signals are large and the standard laser Doppler signal processor can be used to measure the velocity difference and local velocity in real time. The new technique will have various applications in the general area of fluid dynamics.

physics.flu-dyn↗