Exchange-coupled perpendicular media

Abstract

The potential of exchange spring bilayers and graded media is reviewed. An analytical model for the optimization of graded media gives an optimal value of the magnetic polarization of J s = 0.8 T. The optimum design allows for thermally stable grains with grain diameters in the order of 3.3 nm, which supports ultra high density up to 5 -10 Tbit/inch².The switching field distribution is significantly reduced in bilayer media and graded media compared to single phase media. For the graded media the switching field distribution is reduced by about a factor of two. For bilayer media the minimum switching field distribution is obtained for soft layer anisotropies about 1/5 of the hard layer anisotropy. The influence of precessional switching on the reversal time and the reversal field is investigated in detail for magnetic bilayers. Exchange spring bilayers can be reversed with field pulses of 20 ps.

Thermally activated switching at long time scales in exchange-coupled magnetic grains

“…[3][4][5][6][7][8] The desired effect is to be able to use the very strong anisotropy of a hard layer to enhance the grains thermal stability and hence prevent data loss due to thermally activated grain reversal. The hard layer is then exchange coupled to a layer with lower anisotropy, the soft layer.…”

“…[3][4][5][6][7][8] This can be defined as the ratio between the energy barrier E B (thermal stability) and saturation field (switching energy) at a particular sweep rate as,…”

“…Modern exchange-coupled composite (ECC) recording media is composed of a high anisotropy 'hard' layer exchange coupled to one or more lower anisotropy 'soft' layers. [3][4][5][6][7][8][9] One of the most important applications of micromagnetic modeling is the characterization of recording media through M H hysteresis loops. Often, model parameters are determined by fitting results to experimental data.…”

Магнитные и мессбауэровские исследования многослойных структур L1-=SUB=-0-=/SUB=--FePt/Fe/Та

“…В качестве одного из слоев боль-шое внимание привлекают магнитоупорядоченные тон-кие пленки FePt, являющиеся перспективным мате-риалом для магнитотвердого слоя в носителях ин-формации вследствие большой кристаллографической анизотропии (∼ 7 · 10 7 erg/cm 3 ) [1,3]. В последние го-ды проведен ряд теоретических [4][5][6] и эксперимен-тальных исследований многослойных систем на осно-ве FePt, например L1 0 -FePt/CoCrPt [7], магнитожест-ких сплавов FePtCu и многослойных пленок Co/Pt [8], пленок L1 0 -FePt/FeRh [9], L1 0 -FePt/TiN [10], обменно-связанных магнитных нанокомпозитов FePt/Fe 3 Pt [11] и FePt/FePt 3 [12], тонких пленок FePt/BN [13] и L1 0 -FePt/Fe [14][15][16][17][18][19][20][21]. Среди исследуемых материалов мно-гослойная система FePt/Fe отличается малой константой магнитокристаллической анизотропии и большой поля-ризацией магнитного насыщения Fe, что может привести к значительному повышению остаточной намагниченно-сти обменно-связанных магнитотвердых/магнитомягких двухслойных систем [14,22].…”

Effective anisotropy gradient in pressure graded [Co/Pd] multilayers

“…3 Since, such "graded anisotropy" magnetic multilayers have been studied both theoretically [4][5][6][7] and experimentally, including for multilayers where the anisotropy profile was controlled by varying layer thickness, 8 composition, 9 and substrate temperature.…”