Bogdan Valcu - Academia.edu (original) (raw)
Papers by Bogdan Valcu
2023 IEEE International Magnetic Conference - Short Papers (INTERMAG Short Papers)
IEEE Transactions on Magnetics
This dissertation uses both micromagnetic simulation and analytical methods to analyze several as... more This dissertation uses both micromagnetic simulation and analytical methods to analyze several aspects of a perpendicular recording system. To increase the head field amplitude, the recording layer is grown on top of a soft magnetic layer (keeper). There is concern about the ability of the keeper to conduct the magnetic flux from the head at high data rates. We compute
Journal of Applied Physics, 2006
IEEE Transactions on Magnetics, 2002
The paper theoretically examines playback characteristics of a giant magnetoresistive (GMR) head ... more The paper theoretically examines playback characteristics of a giant magnetoresistive (GMR) head for perpendicular recorded magnetization transitions with a soft underlayer. The magnetic scalar potential, calculated numerically by the finite-element method, is fitted to a simple formula involving geometry-dependent parameters. The reciprocity principle leads to the shape of the single pulse signal. For high permeability of the underlayer the pulse has an error function-type dependence on distance. Within this approximation, the paper derives simple formulas for the pulsewidth 50 , 50 , and transition-noise-limited signal-to-noise ratio.
IEEE Transactions on Magnetics, 2004
A micromagnetic model for the writing process in perpendicular magnetic recording is developed to... more A micromagnetic model for the writing process in perpendicular magnetic recording is developed to study the effect of the soft underlayer on the dynamic reversal of the recording layer. The upper part of the soft material is discretized micromagnetically, each spin following LLG dynamics; the remaining part has infinite permeability. The validity of the model is tested in the static case. Dynamically, high-frequency spin motion is observed in the soft layer. Nevertheless, the field inside the data layer follows the time dependence of the input waveform.
IEEE Transactions on Magnetics, 2011
IEEE Transactions on Magnetics, 2009
IEEE Transactions on Magnetics, 2002
The playback signal characteristics in perpendicular recording is analyzed using three-dimensiona... more The playback signal characteristics in perpendicular recording is analyzed using three-dimensional geometry. Analytical expressions are deduced for both the width of the pulse and the asymptotic value taken by the signal when the sensor is far away from the transition.
IEEE International Digest of Technical Papers on Magnetics Conference
ABSTRACT Summary form only given. The general form for the single pulse in perpendicular recordin... more ABSTRACT Summary form only given. The general form for the single pulse in perpendicular recording is well understood. Here we give a quantitative analysis of the signal dependence on specific parameters. Neglecting edge effects, a 2D geometry is assumed. Due to the asymmetry in the construction of the head, the sensor is off-centered, with one gap (shield-to-element) distance g1=gδ typically double the other gap distance g2=g - δ. By reciprocity, the signal is the convolution of the magnetic charge distribution at the two surfaces of the perpendicular medium and the potential along these surfaces. Using finite element software, the potential at the ABS surface of the head is characterized for a range of SUL permeabilities and head geometries. The total flux through the sensor is the inverse Fourier transform of the product of the surface potential, a spacing factor and the magnetization transition derivative transform (we assumed a 'tanh' transition).
IEEE Transactions on Magnetics
The function of two types of magnetic inhomogeneity employed in perpendicular magnetic recording ... more The function of two types of magnetic inhomogeneity employed in perpendicular magnetic recording media designs are analyzed. Continuous granular composite (CGC) media have variable lateral exchange coupling (Hex) through the thickness of the magnetic layers, which can reduce coercivity (Hc) and narrow switching field distribution (SFD). Exchange coupled composite (ECC) media have variable crystalline anisotropy field (Hk) and interlayer exchange coupling (J) through the film thickness, which also reduces Hc. Interactions between the Hk, Hex, and J values of combined ECC+CGC media are presented. The optimum anisotropy profile for conventional ECC media is found to be different than previously modeled. A CGC layer included in the ECC media architecture is shown to change the optimal anisotropy profile and interlayer coupling values.
IEEE Transactions on Magnetics, 2014
IEEE Transactions on Magnetics, 2014
2023 IEEE International Magnetic Conference - Short Papers (INTERMAG Short Papers)
IEEE Transactions on Magnetics
This dissertation uses both micromagnetic simulation and analytical methods to analyze several as... more This dissertation uses both micromagnetic simulation and analytical methods to analyze several aspects of a perpendicular recording system. To increase the head field amplitude, the recording layer is grown on top of a soft magnetic layer (keeper). There is concern about the ability of the keeper to conduct the magnetic flux from the head at high data rates. We compute
Journal of Applied Physics, 2006
IEEE Transactions on Magnetics, 2002
The paper theoretically examines playback characteristics of a giant magnetoresistive (GMR) head ... more The paper theoretically examines playback characteristics of a giant magnetoresistive (GMR) head for perpendicular recorded magnetization transitions with a soft underlayer. The magnetic scalar potential, calculated numerically by the finite-element method, is fitted to a simple formula involving geometry-dependent parameters. The reciprocity principle leads to the shape of the single pulse signal. For high permeability of the underlayer the pulse has an error function-type dependence on distance. Within this approximation, the paper derives simple formulas for the pulsewidth 50 , 50 , and transition-noise-limited signal-to-noise ratio.
IEEE Transactions on Magnetics, 2004
A micromagnetic model for the writing process in perpendicular magnetic recording is developed to... more A micromagnetic model for the writing process in perpendicular magnetic recording is developed to study the effect of the soft underlayer on the dynamic reversal of the recording layer. The upper part of the soft material is discretized micromagnetically, each spin following LLG dynamics; the remaining part has infinite permeability. The validity of the model is tested in the static case. Dynamically, high-frequency spin motion is observed in the soft layer. Nevertheless, the field inside the data layer follows the time dependence of the input waveform.
IEEE Transactions on Magnetics, 2011
IEEE Transactions on Magnetics, 2009
IEEE Transactions on Magnetics, 2002
The playback signal characteristics in perpendicular recording is analyzed using three-dimensiona... more The playback signal characteristics in perpendicular recording is analyzed using three-dimensional geometry. Analytical expressions are deduced for both the width of the pulse and the asymptotic value taken by the signal when the sensor is far away from the transition.
IEEE International Digest of Technical Papers on Magnetics Conference
ABSTRACT Summary form only given. The general form for the single pulse in perpendicular recordin... more ABSTRACT Summary form only given. The general form for the single pulse in perpendicular recording is well understood. Here we give a quantitative analysis of the signal dependence on specific parameters. Neglecting edge effects, a 2D geometry is assumed. Due to the asymmetry in the construction of the head, the sensor is off-centered, with one gap (shield-to-element) distance g1=gδ typically double the other gap distance g2=g - δ. By reciprocity, the signal is the convolution of the magnetic charge distribution at the two surfaces of the perpendicular medium and the potential along these surfaces. Using finite element software, the potential at the ABS surface of the head is characterized for a range of SUL permeabilities and head geometries. The total flux through the sensor is the inverse Fourier transform of the product of the surface potential, a spacing factor and the magnetization transition derivative transform (we assumed a 'tanh' transition).
IEEE Transactions on Magnetics
The function of two types of magnetic inhomogeneity employed in perpendicular magnetic recording ... more The function of two types of magnetic inhomogeneity employed in perpendicular magnetic recording media designs are analyzed. Continuous granular composite (CGC) media have variable lateral exchange coupling (Hex) through the thickness of the magnetic layers, which can reduce coercivity (Hc) and narrow switching field distribution (SFD). Exchange coupled composite (ECC) media have variable crystalline anisotropy field (Hk) and interlayer exchange coupling (J) through the film thickness, which also reduces Hc. Interactions between the Hk, Hex, and J values of combined ECC+CGC media are presented. The optimum anisotropy profile for conventional ECC media is found to be different than previously modeled. A CGC layer included in the ECC media architecture is shown to change the optimal anisotropy profile and interlayer coupling values.
IEEE Transactions on Magnetics, 2014
IEEE Transactions on Magnetics, 2014