Abstract
The development of high-density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat-assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc , coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2 CoSb is introduced as a new hard magnet with potential for thin-film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m-3 is combined with a saturation magnetization of μ0 Ms = 0.52 T at 2 K (2.2 MJ m-3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare-earth-free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin-orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m-1 K-1 , make Rh2 CoSb a candidate for the development of heat-assisted writing with a recording density in excess of 10Tb in.-2 .
Highlights
The development of high-density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals
The pace of doubling of information density on magnetic recording media has slackened in recent years, as the effective size of the perpendicularly recorded grains approached the superparamagnetic blocking diameter, which is the lower size limit for stable ferromagnetism, directly related to the magnetocrystalline anisotropy energy K1
To resist demagnetization by random thermal fluctations, the volume V of a magnetic material must satisfy the empirical condition that K1V/kBT > 60 (K1V > 1.5 eV), where kB and T are the Boltzmann constant and ambient temperature, respectively.[1,2,3]
Summary
Slow cubic to tetragonal phase transition temperature (Tcub-tet) should be above the melting point. The anisotropic thermal conductivity, especial its large c axis value of 20 W m−1 K−1, which is much larger than that of the current FePt HAMR material, is important for cooling, and could lead to a 6.8 times faster writing speed than FePt. Unlike FePt with its order/disorder phase transition, Rh2CoSb is a stable phase without any structural transition below the melting point and its properties are stable in air. Unlike FePt with its order/disorder phase transition, Rh2CoSb is a stable phase without any structural transition below the melting point and its properties are stable in air All these features commend Rh2CoSb as a candidate for HAMR media with a recording density of more than 10 Tb in.−2 and high writing speed
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