Talk

Friday, July 17th, 2015

Speaker

Dieter Weller

Affiliation

HGST, a Western Digital Company, USA

Title

Future FePt Heat Assisted Magnetic Recording Technology

Location

Department of Computer Science, Voutes, Room A115 (basement)

Time

16:00

Language

English

Abstract

The focus is on heat-assisted magnetic recording (HAMR) media requirements and challenges to extend the areal density (AD) beyond recently achieved 1.4 Tb/in² [1]. Granular high anisotropy chemically ordered and well textured L10 FePtX-Y perpendicular HAMR media with an average grain size =6-10 nm, size distribution σD/D ~ 16-25% and Curie temperature distribution σTC/TC < 3% will be discussed. Reducing down to 3-5 nm and achieving σD/D <10-15% in principal allows increasing AD up to about 4 Tb/in² [2]. X~ 10at% Cu or Ni reduces the Curie temperature by ~100 K below TC,bulk=750 K and lowers the recording energy requirement. Grain segregants like Y=C, BN, SiO₂ and TiO₂ exchange decouple grains and achieve dominant perpendicular thermal conductivity. 10 nm thick fcc MgO(100) seed layers generate tensile stress in FePt which is grown at elevated temperature of 650°C on glass substrates and facilitates the formation of well- oriented grains. A c/a lattice parameter ratio close to 0.96 is consistent with chemical ordering > 90% and leads to high perpendicular magnetic anisotropy Ku > 5.107 erg/cm³ [2]. High resolution STEM and EELS and high field > 10T hysteresis measurements are key experimental activities needed to characterize and optimize HAMR media [3,4].

The talk will include recent media modeling activities [5] and another important topic based on femtosecond magneto-optics, which allows investigation of the dynamical properties of granular FePt with temporal resolution in the time scale of a few picoseconds [6].

[1] Ganping Ju et al., Seagate Intermag 2015 presentation in Beijing; IEEE Trans Mag. (to be published)

[2] D. Weller et al., pss A, 210, 1245, (2013) & D. Weller et al., IEEE Trans Mag 50, 3100108 (2014)

[3] S. Wicht et al., J. Appl. Phys. 114, 063906 (2013) & J. Appl. Phys. 117, 013907 (2015)

[4] J. Becker et al., Appl. Phys. Lett. 104, 069416 (2014)

[5] A. Lyberatos, et al., J. Appl. Phys. 114, 233904 (2013); IEEE Trans. Mag., 2104 304 (2014); J. Appl. Phys. 117, 133905 (2015)

[6] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996) & J.-Y. Bigot et al., Annalen Physik 525, 2 (2013)

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