54 research outputs found
Negative tunneling magnetoresistance by canted magnetization in MgO/NiO tunnel barriers
The influence of insertion of an ultra-thin NiO layer between the MgO barrier
and ferromagnetic electrode in magnetic tunnel junctions has been investigated
by measuring the tunneling magnetoresistance and the X-ray magnetic circular
dichroism (XMCD). The magnetoresistance shows a high asymmetry with respect to
bias voltage, giving rise to a negative value of -16% at 2.8 K. We attribute
this to the formation of non-collinear spin structures in the NiO layer as
observed by XMCD. The magnetic moments of the interface Ni atoms tilt from the
easy axis due to exchange interaction and the tilting angle decreases with
increasing the NiO thickness. The experimental observations are further support
by non-collinear spin density functional theory
Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields
We present a comprehensive experimental and numerical study of magnetization
dynamics triggered in a thin metallic film by single-cycle terahertz pulses of
MV/m electric field amplitude and ps duration. The
experimental dynamics is probed using the femtosecond magneto-optical Kerr
effect (MOKE), and it is reproduced numerically using macrospin simulations.
The magnetization dynamics can be decomposed in three distinct processes: a
coherent precession of the magnetization around the terahertz magnetic field,
an ultrafast demagnetization that suddenly changes the anisotropy of the film,
and a uniform precession around the equilibrium effective field that is relaxed
on the nanosecond time scale, consistent with a Gilbert damping process.
Macrospin simulations quantitatively reproduce the observed dynamics, and allow
us to predict that novel nonlinear magnetization dynamics regimes can be
attained with existing table-top terahertz sources.Comment: 6 pages, 4 figure
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