291 research outputs found
Surface morphology and magnetic anisotropy in (Ga,Mn)As
Atomic Force Microscopy and Grazing incidence X-ray diffraction measurements
have revealed the presence of ripples aligned along the direction
on the surface of (Ga,Mn)As layers grown on GaAs(001) substrates and buffer
layers, with periodicity of about 50 nm in all samples that have been studied.
These samples show the strong symmetry breaking uniaxial magnetic anisotropy
normally observed in such materials. We observe a clear correlation between the
amplitude of the surface ripples and the strength of the uniaxial magnetic
anisotropy component suggesting that these ripples might be the source of such
anisotropy.Comment: 3 pages, 4 figures, 1 table. Replaced with published versio
Strain Induced Vortex Core Switching in Planar Magnetostrictive Nanostructures
The dynamics of magnetic vortex cores is of great interest because the gyrotropic mode has applications in spin torque driven magnetic microwave oscillators, and also provides a means to flip the direction of the core for use in magnetic storage devices. Here, we propose a new means of stimulating magnetization reversal of the vortex core by applying a time-varying strain gradient to planar structures of the magnetostrictive material Fe81Ga19 (Galfenol), coupled to an underlying piezoelectric layer. Using micromagnetic simulations we have shown that the vortex core state can be deterministically reversed by electric field control of the time-dependent strain-induced anisotropy
Quantified academic selves: The gamification of science through social networking services
Introduction. Our study critically engages with techniques of self-quantification in contemporary academia, by demonstrating how social networking services enact research and scholarly communication as a 'game'.
Method. The empirical part of the study involves an analysis of two leading platforms: Impactstory and ResearchGate. Observed qualities of these platforms will be analyzed in detail with concrete examples of gaming features in focus. Subsequently, we relate the development of these digital platforms to a broader 'quantified self movement'. Special attention will also be paid to how these platforms contribute to a general quantification of the academic (authorial) self.
Theory. Theoretically we relate the 'gamification' of research to neoliberal ideas about markets and competition. Our analysis then extends to long-standing and fundamental ideas about self-betterment expressed in the philosophy of Peter Sloterdijk.
Findings. Our study shows how social networking services, such as ResearchGate and Impactstory, enact researchers as 'entrepreneurs of themselves' in a marketplace of ideas, and the quantification of scholarly reputation to a single number plays an important role in this process. Moreover, the technologies that afford these types of quantifiable interactions affect the 'unfolding ontology' of algorithmic academic identities.
Conclusions. The gamification of quantified academic selves intensifies the competitive nature of scholarship, it commodifies academic outputs and it might lead to goal displacement and cheating. However, self-quantification might also serve as a liberating and empowering activity for the individual researcher as alternative measures of impact and productivity are provided by these platforms.Merit, Expertise and Measuremen
Voltage control of magnetocrystalline anisotropy in ferromagnetic - semiconductor/piezoelectric hybrid structures
We demonstrate dynamic voltage control of the magnetic anisotropy of a
(Ga,Mn)As device bonded to a piezoelectric transducer. The application of a
uniaxial strain leads to a large reorientation of the magnetic easy axis which
is detected by measuring longitudinal and transverse anisotropic
magnetoresistance coefficients. Calculations based on the mean-field
kinetic-exchange model of (Ga,Mn)As provide microscopic understanding of the
measured effect. Electrically induced magnetization switching and detection of
unconventional crystalline components of the anisotropic magnetoresistance are
presented, illustrating the generic utility of the piezo voltage control to
provide new device functionalities and in the research of micromagnetic and
magnetotransport phenomena in diluted magnetic semiconductors.Comment: Submitted to Physical Review Letters. Updates version 1 to include a
more detailed discussion of the effect of strain on the anisotropic
magnetoresistanc
Anisotropic Magnetoresistance components in (Ga,Mn)As
Our experimental and theoretical study of the non-crystalline and crystalline
components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As is aimed at
exploring the basic physical aspects of this relativistic transport effect. The
non-crystalline AMR reflects anisotropic lifetimes of the holes due to
polarized Mn impurities while the crystalline AMR is associated with valence
band warping. We find that the sign of the non-crystalline AMR is determined by
the form of spin-orbit coupling in the host band and by the relative strengths
of the non-magnetic and magnetic contributions to the impurity potential. We
develop experimental methods directly yielding the non-crystalline and
crystalline AMR components which are then independently analyzed. We report the
observation of an AMR dominated by a large uniaxial crystalline component and
show that AMR can be modified by local strain relaxation. We discuss generic
implications of our experimental and theoretical findings including predictions
for non-crystalline AMR sign reversals in dilute moment systems.Comment: 4 pages, 3 figures. Phys. Rev. Lett. in pres
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