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The open physics laboratory and characteristics of effective teaching assistants
The problem of this study involves identifying and ranking in importance the characteristics of effective teaching assistants in the learning environment of an open physics instructional laboratory
Symmetry broken spin reorientation transition in epitaxial MgO/Fe/MgO layers with competing anisotropies
The observation of perpendicular magnetic anisotropy (PMA) at MgO/Fe interfaces boosted the development of spintronic devices based on ultrathin ferromagnetic layers. Yet, magnetization reversal in the standard magnetic tunnel junctions (MTJs) with competing PMA and in-plane anisotropies remains unclear. Here we report on the field induced nonvolatile broken symmetry magnetization reorientation transition from the in-plane to the perpendicular (out of plane) state at temperatures below 50 K. The samples were 10 nm thick Fe in MgO/Fe(100)/MgO as stacking components of V/MgO/Fe/MgO/Fe/Co double barrier MTJs with an area of 20 × 20 μm2. Micromagnetic simulations with PMA and different second order anisotropies at the opposite Fe/MgO interfaces qualitatively reproduce the observed broken symmetry spin reorientation transition. Our findings open the possibilities to develop multistate epitaxial spintronics based on competing magnetic anisotropies.This work has been supported in part by Spanish MINECO (MAT2015-66000-P, EUIN2017-87474), SPINORBIT (MDM-2014-0377) and Comunidad de Madrid (NANOFRONTMAG-CM
S2013/MIT-2850). C.T. acknowledges “EMERSPIN” grant ID PN-III-P4-ID-PCE-2016-0143, No. UEFISCDI:22/12.07.201
Controlling shot noise in double-barrier magnetic tunnel junctions
We demonstrate that shot noise in Fe/MgO/Fe/MgO/Fe double-barrier magnetic
tunnel junctions is determined by the relative magnetic configuration of the
junction and also by the asymmetry of the barriers. The proposed theoretical
model, based on sequential tunneling through the system and including spin
relaxation, successfully accounts for the experimental observations for bias
voltages below 0.5V, where the influence of quantum well states is negligible.
A weak enhancement of conductance and shot noise, observed at some voltages
(especially above 0.5V), indicates the formation of quantum well states in the
middle magnetic layer. The observed results open up new perspectives for a
reliable magnetic control of the most fundamental noise in spintronic
structures.Comment: 8 pages, 4 figure
Two types of all-optical magnetization switching mechanisms using femtosecond laser pulses
Magnetization manipulation in the absence of an external magnetic field is a
topic of great interest, since many novel physical phenomena need to be
understood and promising new applications can be imagined. Cutting-edge
experiments have shown the capability to switch the magnetization of magnetic
thin films using ultrashort polarized laser pulses. In 2007, it was first
observed that the magnetization switching for GdFeCo alloy thin films was
helicity-dependent and later helicity-independent switching was also
demonstrated on the same material. Recently, all-optical switching has also
been discovered for a much larger variety of magnetic materials (ferrimagnetic,
ferromagnetic films and granular nanostructures), where the theoretical models
explaining the switching in GdFeCo films do not appear to apply, thus
questioning the uniqueness of the microscopic origin of all-optical switching.
Here, we show that two different all-optical switching mechanisms can be
distinguished; a "single pulse" switching and a "cumulative" switching process
whose rich microscopic origin is discussed. We demonstrate that the latter is a
two-step mechanism; a heat-driven demagnetization followed by a
helicity-dependent remagnetization. This is achieved by an all-electrical and
time-dependent investigation of the all-optical switching in ferrimagnetic and
ferromagnetic Hall crosses via the anomalous Hall effect, enabling to probe the
all-optical switching on different timescales.Comment: 1 page, LaTeX; classified reference number
All-optical control of ferromagnetic thin films and nanostructures
The interplay of light and magnetism has been a topic of interest since the
original observations of Faraday and Kerr where magnetic materials affect the
light polarization. While these effects have historically been exploited to use
light as a probe of magnetic materials there is increasing research on using
polarized light to alter or manipulate magnetism. For instance deterministic
magnetic switching without any applied magnetic fields using laser pulses of
the circular polarized light has been observed for specific ferrimagnetic
materials. Here we demonstrate, for the first time, optical control of
ferromagnetic materials ranging from magnetic thin films to multilayers and
even granular films being explored for ultra-high-density magnetic recording.
Our finding shows that optical control of magnetic materials is a much more
general phenomenon than previously assumed. These results challenge the current
theoretical understanding and will have a major impact on data memory and
storage industries via the integration of optical control of ferromagnetic
bits.Comment: 21 pages, 11 figure
Very low 1/f noise at room temperature in fully epitaxial Fe/MgO/Fe magnetic tunnel junctions
We report on room temperature 1/f noise in fully epitaxial
Fe(45nm)/MgO(2.6nm)/Fe(10nm) magnetic tunnel junctions (MTJs) with and without
carbon doping of the Fe/MgO bottom interface. We have found that the normalized
noise (Hooge factor) asymmetry between parallel and antiparallel states may
strongly depend on the applied bias and its polarity. Both types of MTJs
exhibit record low Hooge factors being at least one order of magnitude smaller
than previously reported.Comment: 9 pages, 3 figure
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