Magnetic Properties of Granular L10 FePt Films for Heat-Assisted Magnetic Recording (HAMR) Applications

TY - CHAP

T1 - Magnetic Properties of Granular L10 FePt Films for Heat-Assisted Magnetic Recording (HAMR) Applications

AU - Papusoi, Cristian

AU - Desai, Mrugesh

AU - Ruta, Sergiu

AU - Chantrell, Roy W.

N1 - Publisher Copyright: © Springer Nature Switzerland AG 2021.

PY - 2021/9/29

Y1 - 2021/9/29

N2 - The merit of heat-assisted magnetic recording (HAMR) that enables to increase the recording density beyond the classical perpendicular magnetic recording (PMR) is a contribution to the writing field gradient additional to that generated by the magnetic writer. This contribution is of thermal origin, and it is proportional to |dHK/dT|T=TW, where H K is the anisotropy field and T W is the writing temperature of the recording medium. In order to improve the sharpness of the recorded transitions, |dHK/dT|T=TW should be increased and the intensity of grain interactions should be decreased. The former requires a judicious choice of the material used for the grain core alloy and also a tight control of the granular medium intrinsic distributions, namely, the grain Curie temperature T C, the H K, and the grain size distributions. In addition to these factors, the grain magnetization reversal mechanism at T W plays an important role on the transition noise. This chapter describes a set of experimental methods used in the characterization of HAMR media, from setup description to experimental data analysis. The temperature dependence of the AC susceptibility measured along the film easy axis is used to evaluate the T C distribution (of average and standard deviation σ TC). Thermal erasure of the remanent magnetization using ns duration laser pulses is used to evaluate σ TC. The dependence of the AC susceptibility on the DC field applied along a hard-axis direction is used to evaluate the H K distribution (of average and standard deviation σ HK) as a function of temperature. A method to evaluate the intensity of intergranular exchange coupling based on high-field polar-Kerr magnetometry is described. The grain magnetization reversal mechanism is investigated based on measurements of thermal stability and of remanence coercivity as a function of temperature. These measurements enable the validation of theoretical concepts regarding the origin and the law governing the temperature dependence of H K in chemically ordered alloys used as HAMR media. The described experimental methodologies are exemplified on a series of samples having the structure glass/seed/heat-sink/MgO/MAG/C, where the MAG layer is an L10 FePt-based granular alloy of 3.8–10.5 nm thickness.

AB - The merit of heat-assisted magnetic recording (HAMR) that enables to increase the recording density beyond the classical perpendicular magnetic recording (PMR) is a contribution to the writing field gradient additional to that generated by the magnetic writer. This contribution is of thermal origin, and it is proportional to |dHK/dT|T=TW, where H K is the anisotropy field and T W is the writing temperature of the recording medium. In order to improve the sharpness of the recorded transitions, |dHK/dT|T=TW should be increased and the intensity of grain interactions should be decreased. The former requires a judicious choice of the material used for the grain core alloy and also a tight control of the granular medium intrinsic distributions, namely, the grain Curie temperature T C, the H K, and the grain size distributions. In addition to these factors, the grain magnetization reversal mechanism at T W plays an important role on the transition noise. This chapter describes a set of experimental methods used in the characterization of HAMR media, from setup description to experimental data analysis. The temperature dependence of the AC susceptibility measured along the film easy axis is used to evaluate the T C distribution (of average and standard deviation σ TC). Thermal erasure of the remanent magnetization using ns duration laser pulses is used to evaluate σ TC. The dependence of the AC susceptibility on the DC field applied along a hard-axis direction is used to evaluate the H K distribution (of average and standard deviation σ HK) as a function of temperature. A method to evaluate the intensity of intergranular exchange coupling based on high-field polar-Kerr magnetometry is described. The grain magnetization reversal mechanism is investigated based on measurements of thermal stability and of remanence coercivity as a function of temperature. These measurements enable the validation of theoretical concepts regarding the origin and the law governing the temperature dependence of H K in chemically ordered alloys used as HAMR media. The described experimental methodologies are exemplified on a series of samples having the structure glass/seed/heat-sink/MgO/MAG/C, where the MAG layer is an L10 FePt-based granular alloy of 3.8–10.5 nm thickness.

KW - AC susceptibility

KW - Coherent and incoherent magnetization reversal

KW - Curie temperature

KW - Heat-assisted magnetic recording

KW - L10 FePt

KW - Pump-probe measurements

UR - http://www.scopus.com/inward/record.url?scp=85160466326&partnerID=8YFLogxK

U2 - 10.1007/978-3-030-70443-8_25

DO - 10.1007/978-3-030-70443-8_25

M3 - Chapter

AN - SCOPUS:85160466326

SN - 9783030704421

SP - 751

EP - 770

BT - Magnetic Measurement Techniques for Materials Characterization

PB - Springer International Publishing AG

ER -