Research On The Chemical Ordering Of L1₀ Films

Based on the progress of data storage,both computer and internet develop fast. As a result,the volume and transmission speed of information increase sharply.As a major storage method,magnetic recording gains universal interest from both scientific and technological field.Nowadays,in the HDD market,the recording density has increased from 2Kbit/in² in 1957 to 329Gbit/in².What's more,the recording density has even reached 450Gbit/in²,which means the size of single recording unit having been reduced to the scale of several nanometers.The goal of the industry is 1T/in². However,the superparamagnetic effect is the fundamental factor limiting the achievement of the goal.In order to conquer superparamagnetic effect,the most important thing is to explore new materials with high magneto-crystalline anisotropy (Ku).L1₀ phase FePt andÏ„phase MnAl's Ku are 7×10⁷erg/cc and 1×10⁷erg/cc respectively,so they are promising materials for future ultra-high recording density industry.Unfortunately,the as-deposited FePt film always forms disordered A1 phase, which is soft magnetic with fcc structure.In order to achieve L1₀ phase,the film need to be annealed under high temperature.So,it's the key point to develop new methods to fabricate L1₀ phase FePt film under lower temperature.The first part of the paper is kicked off under this background.The influences of a Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated.Compared with single FePt alloy films,a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L1₀ FePt films.Moreover,the coercivity increases when a thin Fe layer covers on the FePt layer.Beyond a critical thickness,however,the Fe cover layer quickens the magnetization reversal of Fe₄₉Pt₅₁/Fe bi-layers by their exchange coupling.In the as-deposited MnAl film,there are not only ferromagneticÏ„phase,but also existing some non-ferromagnetic phases such asε-MnAl.In order to satisfy the requirements of ultra-high recording density materials,we need to explore the factors affecting the formation ofÏ„phase to eliminate those non-ferromagnetic phases.The other part of the paper is carried out to solve this problem.The structural and magnetic properties ofÏ„-MnAl alloy films as well as the affection of the substrate are studied.The films are derived by annealing from Mn/Al multi-layers.Ï„-MnAl appears when the annealing temperature increases up to 350℃, but decomposes intoγ2-MnAl andβ-Mn at 500℃annealing.Good magnetic properties are obtained after 400～450℃annealing.Furthermore,Ï„-MnAl forms in the Mn-Al interface.The saturation magnetization M_S increases firstly with the thickness of Mn(or Al) layers,and then decreases in inverse proportion to that of Mn(or Al) layers.The turning point implies that the thickness ofÏ„-MnAl is no more than 5 nm in the Mn₆₀Al₄₀ films.By depositing a Mn/Al buffer layer on the heated GaAs substrate, the magnetic properties and orientation of the film are improved.