ELFT HÍRADÓ

[tcsaba AT eik.bme.hu]

                   M E G H Í V Ó - I N V I T A T I O N

     Seminar series of the Department of Theoretical Physics at the
           Budapest University of Technology and Economics

                            Andrea Meo
                      (University of York)

          Atomistic modelling of magnetic reversal mechanisms
                    in CoFeB-MgO tunnel junctions


Magnetic Random Access Memory (MRAM) is a non-volatile memory  
technology utilizing a magnetic tunnel junction (MTJ) to sense the  
magnetic state. A promising material for MRAM is a MTJ consisting of  
CoFeB/MgO due to its strong thermal stability, low damping and high  
tunnelling magnetoresistance [1]. Here we investigate the intrinsic  
material properties of CoFeB/MgO bilayers using an atomistic spin  
model[2]. The system consists of a single high anisotropy monolayer in  
contact with MgO due to the perpendicular magnetic anisotropy (PMA),  
and a thicker bulk layer with very low anisotropy. Due to the strong  
variation of the anisotropy one would expect non-collinear reversal  
modes, particularly at sizes beyond the single domain limit and at  
elevated temperatures. We have systematically investigated the effects  
of temperature, system size and thickness on the coercivity of the  
system. In a low temperature limit the reversal is deterministic and  
coherent with an increase of the coercivity (Hc) up to very small dot  
dimensions, while for large dot size the reversal becomes incoherent.  
At higher temperatures the nucleation is the dominant reversal  
mechanism above the single domain size and Hc tends to a constant  
value for big systems. The overall study shows that reversal process  
is incoherent for large particles and that the temperature is a major  
factor in the switching causing the reversal to be thermally nucleated  
in a moderate temperature regime. Moreover it is not possible to  
establish unique critical domain size and energy barrier.

[1] Ikeda,S. et al. A perpendicular-anisotropy CoFeB–MgO magnetic  
tunnel junction. Nature Materials 9, 721–724 (2010).

[2] R. F. L. Evans, W. J. Fan, P. Chureemart, T. A. Ostler, M. O. A.  
Ellis and R. W. Chantrell, J. Phys.: Condens. Matter 26, 103202 (2014)


Idöpont: 2015. szeptember 18., 10:15
Helyszín:
BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsöház, szemináriumi szoba


----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.