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Magnetization Reversal of Synthetic Antiferromagnets Using
Magnetic Field Pulse Perpendicular to Reference Plane
Dzhezherya Yu.1, Iurchuk V. 2, Demishev K.2, Korenivski V. 3
Institute of Magnetism, National Academy of Sciences of Ukraine, Kiev, Ukraine
National Technical University of Ukraine “Kiev polytechnic institute”, Kiev, Ukraine
Royal Institute of Technology, Stockholm, Sweden
The properties of novel systems – so-called synthetic antiferromagnets
(SAF) which are the basic elements for magnetoresistive random-access
memory (MRAM) cells – are widely studied now. SAF consists of two dipolecoupled elliptical magnetic layers with a small aspect ratio separated by thin
non-magnetic spacer. Previous works devoted to the investigation of spin
dynamics revealed collective acoustical and optical spin resonant modes in such
systems. High-frequency investigations of the two coupled macrospins in SAF
cell showed that system’s behavior is similar to Kapitsa pendulum. In-plane AC
magnetic field was proposed to use for the cell’s state operation.
Here we study the magnetization dynamics of SAF for the case when the
external magnetic field is perpendicular to cell’s basic plane. Switching
conditions between SAF’s equilibrium states have been considered. It has been
shown that at definite conditions a high-speed switching without any relaxation
processes can take place.
A major problem in controlling the magnetization process in SAF is to
organize a switching between two ground states with opposite values of
antiferromagnetism vector to avoid long-lasting relaxation processes. Analysis
of SAF dynamics equations in different external perpendicular magnetic field
configurations allows deriving an optimal profile for the excitation field as
H ( t ) = − H ch ( t ) ,
where H 0 is the field amplitude and is the pulse duration parameter. No
relaxation oscillations near the new equilibrium state should be observed for
such field profile. The amplitude of the external field can be reduced by
adjusting of the duration parameter, which is extremely important for MRAM
operation. It should be noted that remagnetization can be done using the field
pulses with the shape close to (*) (e. g. Gaussian or Lorentzian) but in this case
we cannot totally avoid the damping oscillations during transition to the new
SAF state.
The possibility to operate SAF cell using by means of perpendicular
magnetic field pulses has been demonstrated. It has been shown that
remagnetization of the system can be realized in non-inertial mode using field
signals of a specific shape.