Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions

We present a theoretical description of the thermopower due to magnon-assisted tunneling in a mesoscopic tunnel junction between two ferromagnetic metals. The thermopower is generated in the course of thermal equilibration between two baths of magnons, mediated by electrons. For a junction between two ferromagnets with antiparallel polarizations, the ability of magnon-assisted tunneling to create thermopower $S_{AP}$ depends on the difference between the size $\Pi_{\uparrow, \downarrow}$ of the majority and minority band Fermi surfaces and it is proportional to a temperature dependent factor $(k_{B}T/\omega_{D})^{3/2}$ where $\omega_{D}$ is the magnon Debye energy. The latter factor reflects the fractional change in the net magnetization of the reservoirs due to thermal magnons at temperature $T$ (Bloch's $T^{3/2}$ law). In contrast, the contribution of magnon-assisted tunneling to the thermopower $S_P$ of a junction with parallel polarizations is negligible. As the relative polarizations of ferromagnetic layers can be manipulated by an external magnetic field, a large difference $\Delta S = S_{AP} - S_P \approx S_{AP} \sim - (k_B/e) f (\Pi_{\uparrow},\Pi_{\downarrow}) (k_BT/\omega_{D})^{3/2}$ results in a magnetothermopower effect. This magnetothermopower effect becomes giant in the extreme case of a junction between two half-metallic ferromagnets, $\Delta S \sim - k_B/e$.Comment: 9 pages, 4 eps figure

Labor Productivity: Structural Change and Cyclical Dynamics

A longstanding issue in empirical economics is the behavior of average labor productivity over the business cycle. This paper provides new insights into the cyclicality of aggregate labor productivity by examining the cyclical behavior of productivity at the plant level as well as the role of reallocation across plants over the cycle. We find that plant-level productivity is even more procyclical than aggregate productivity, because short-run reallocation yields a countercyclical contribution to labor productivity. At the plant level, we find that cyclicality of productivity varies systematically with long-run employment growth. Over the course of the cycle, plants that are long-run downsizers exhibit significantly greater procyclicality of productivity than do long-run upsizers. When we control for the direction of a cyclical shock, we find that the fall in productivity from an adverse cyclical shock for long-run downsizers is significantly larger in magnitude than is the fall in productivity from an equivalent adverse cyclical shock for long-run upsizers. We argue that these findings raise questions about one of the most popular explanations of procyclical productivity: changing factor utilization over the cycle

Measurement issues, the productivity slowdown, and the explosion of computer power

2.00SIGLEAvailable from British Library Document Supply Centre- DSC:3597.9512(CEPR-DP--305) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

A tale of two cycles: closure, downsizing and productivity growth in UK manufacturing, 1973-89

This article uses the ARD, the new longitudinal database of the Census of Production, to analyse productivity at the establishment level in the two cycles of I973-9 and 1979-89. Contrary to a commonly held view, closures did not play a major role in accounting for productivity growth in 1979-89. Establishments which shut had lower productivity than survivors but the exits were replaced by entrants whose productivity was also lower. Hence most of productivity growth was due to growth within survivors. Most productivity growth occurred in establishments which reduced employment. But despite an overall fall of a quarter in employment, 16 per cent of productivity growth occurred in establishments which expanded employment. The main difference between 1973-9 and 1979-89 was in the productivity growth rate amongst survivors. In 1973-9, it was negative overall and over half of employment in I973 was in establishments where productivity subsequently fell