444 research outputs found
The United Kingdom smart meter rollout through an energy justice lens
The United Kingdom’s Smart Meter Implementation Programme (SMIP) creates the legal framework so that an in-home display unit and a smart gas and electricity meter can be installed in every household by the end of 2020. Intended to reduce household energy consumption, the SMIP is one of the world’s most complex smart meter rollouts. It is also proving to be a challenging one as a series of obstacles has characterised and potentially restricted implementation. This chapter first gives background to the most recent smart meter roll out developments in the UK and second, uses an energy justice framework to explore the emergent challenges under the titles of distributional justice, procedural justice and justice as recognition. Applying this framework to an analysis of the UK SMIP provides opportunities to accurately record, present and expose potential forthcoming injustices. In light of this, we offer a series of policy recommendations
Low-temperature magnetization of (Ga,Mn)As semiconductors
We report on a comprehensive study of the ferromagnetic moment per Mn atom in
(Ga,Mn)As ferromagnetic semiconductors. Theoretical discussion is based on
microscopic calculations and on an effective model of Mn local moments
antiferromagnetically coupled to valence band hole spins. The validity of the
effective model over the range of doping studied is assessed by comparing with
microscopic tight-binding/coherent-potential approximation calculations. Using
the virtual crystal k.p model for hole states, we evaluate the zero-temperature
mean-field contributions to the magnetization from the hole kinetic and
exchange energies, and magnetization suppression due to quantum uctuations of
Mn moment orientations around their mean-field ground state values.
Experimental low-temperature ferromagnetic moments per Mn are obtained by
superconducting quantum interference device and x-ray magnetic circular
dichroism measurements in a series of (Ga,Mn)As semiconductors with nominal Mn
doping ranging from ~2% to 8%. Hall measurements in as-grown and annealed
samples are used to estimate the number of uncompensated substitutional Mn
moments. Based on our comparison between experiment and theory we conclude that
all these Mn moments in high quality (Ga,Mn)As materials have nearly parallel
ground state alignment.Comment: 11 pages, 11 figures, submitted to Phys. Rev.
Reorientation Transition in Single-Domain (Ga,Mn)As
We demonstrate that the interplay of in-plane biaxial and uniaxial anisotropy
fields in (Ga,Mn)As results in a magnetization reorientation transition and an
anisotropic AC susceptibility which is fully consistent with a simple single
domain model. The uniaxial and biaxial anisotropy constants vary respectively
as the square and fourth power of the spontaneous magnetization across the
whole temperature range up to T_C. The weakening of the anisotropy at the
transition may be of technological importance for applications involving
thermally-assisted magnetization switching.Comment: 4 pages, 4 figure
DC-transport properties of ferromagnetic (Ga,Mn)As semiconductors
We study the dc transport properties of (Ga,Mn)As diluted magnetic
semiconductors with Mn concentration varying from 1.5% to 8%. Both diagonal and
Hall components of the conductivity tensor are strongly sensitive to the
magnetic state of these semiconductors. Transport data obtained at low
temperatures are discussed theoretically within a model of band-hole
quasiparticles with a finite spectral width due to elastic scattering from Mn
and compensating defects. The theoretical results are in good agreement with
measured anomalous Hall effect and anisotropic longitudinal magnetoresistance
data. This quantitative understanding of dc magneto-transport effects in
(Ga,Mn)As is unparalleled in itinerant ferromagnetic systems.Comment: 3 pages, 3 figure
Prospects of high temperature ferromagnetism in (Ga,Mn)As semiconductors
We report on a comprehensive combined experimental and theoretical study of
Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad
agreement between theoretical expectations and measured data allows us to
conclude that T_c in high-quality metallic samples increases linearly with the
number of uncompensated local moments on Mn_Ga acceptors, with no sign of
saturation. Room temperature ferromagnetism is expected for a 10% concentration
of these local moments. Our magnetotransport and magnetization data are
consistnent with the picture in which Mn impurities incorporated during growth
at interstitial Mn_I positions act as double-donors and compensate neighboring
Mn_Ga local moments because of strong near-neighbor Mn_Ga-Mn_I
antiferromagnetic coupling. These defects can be efficiently removed by
post-growth annealing. Our analysis suggests that there is no fundamental
obstacle to substitutional Mn_Ga doping in high-quality materials beyond our
current maximum level of 6.2%, although this achievement will require further
advances in growth condition control. Modest charge compensation does not limit
the maximum Curie temperature possible in ferromagnetic semiconductors based on
(Ga,Mn)As.Comment: 13 pages, 12 figures, submitted to Phys. Rev.
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