Stephanie Hernandez

Synthetic antiferromagnet for hard layer of exchange coupled composite media

It has been shown that exchange coupled composite (ECC) media exhibit a superior thermal stability to switching field ratio compared to conventional perpendicular media. However, optimal media designs have employed a low magnetization hard layer. A more physically achievable design may consist of replacing the hard layer with a synthetic antiferromagnet consisting of two ferromagnetic hard layers coupled by an antiferromagnetic exchange interaction. This approach is shown to decrease the switching field and increases the thermal stability ratio when compared to ECC media with a single hard layer.

Feasibility of Recording 1

Exchange coupled composite media has a lower switching field compared to conventional perpendicular media at the same level of thermal stability, making it promising for high areal density recording. In this paper, we propose head and media specifications, calculated micromagnetically at a density of 1 Tb/in2, using a composite media with a synthetic antiferromagnet hard layer. We assume realistic constraints such as jitter to bit length ratio, skew, seed layer, and grain boundaries. T50 of the read back pulse is estimated using a current perpendicular to plane (CPP) giant magnetoresistive (GMR) reader and the magnetization noise is calculated. The signal to dc noise ratio is also estimated for the media used.

{\hbox{Tb/in}}^{2}

An analytic expression that includes the effect of multiple reflections within the interface of a spin-valve composed of materials with partial spin polarization was obtained. Inclusion of this term in a micromagnetic calculation demonstrates the effect of the spin polarization of the magnetic material on the current induced behavior of the structure. We show that neglecting to include interfacial scattering events results in an underestimation of the switching current compared to the method detailed in this letter. Multiple reflections also produce a strong dependence of the switching current on the magnetocrystalline anisotropy of the fixed layer.

Areal Density

An approach for calculating spin transfer torque including interfacial scattering effects in structures consisting of multiple ferromagnet/nonmagnet (FM/NM) bilayers was developed. Using this approach, a micromagnetic analysis on structures consisting of six magnetic layers was compared to electrical measurements on electrodeposited Co/Cu multilayered nanowires. Good agreement with experiment was achieved if it was assumed that one of the layers is magnetically fixed. An array of 16 wires, each consisting of 6 FM/NM bilayers, was also micromagnetically modeled and compared to a similar experimental measurement. Both results confirm that including a wide distribution of wires results in a less uniform switching mechanism.

Calculation of spin transfer torque in partially polarized spin valves including multiple reflections

Abstract Background: Parenting adolescents poses challenges that are exacerbated by immigration. Aqui Para Ti [Here for You] (APT) is a clinic-based, healthy youth development program that provides family-centered care for Latino youth and their families who are mostly immigrants from Mexico and Latin America. Objectives: To present the APT model of care and report the experiences of youth and their parents. Subjects: APT patients between 11 and 24 years (n=30) and parents (n=15). Most youth patients were female, between 11 and 17 years, and from Mexico. Most parents were female, 40 years or younger, and from Mexico. Methods: Youth participants completed a survey and participated in an individual semi-structured interview, and parent participants attended focus groups. Descriptive statistics summarized survey data. Interviews and focus groups were transcribed and analyzed in Spanish using content analysis by two independent coders. Quantitative and qualitative findings were integrated using side-by-side comparisons. Researchers not involved in the coding process contributed with the interpretation of the findings. Results: Youth and parents were satisfied with the services received at APT. Youth felt listened to by their providers (100%), felt they could trust them (100%) and valued comprehensive care. Eighty-seven percent reported that their experiences at APT were better than at other clinics. Parents valued the family parallel care, confidentiality, family-centeredness, and the cultural inclusivity of the APT services. Conclusion: Patients and parents were satisfied with the services offered at APT. Family parallel care could be a positive alternative to deliver confidential and family-centered services to immigrant families.

Micromagnetic calculation of spin transfer torque in Co/Cu multilayer nanowires

The damping constant is a key design parameter in magnetic reader design. Its value can be derived from bulk or sheet film ferromagnetic resonance (FMR) line width. However, dynamics of nanodevices is usually defined by presence of non-uniform modes. It triggers new damping mechanisms and produces stronger damping than expected from traditional FMR. This work proposes a device-level technique for damping evaluation, based on time-domain analysis of thermally excited stochastic oscillations. The signal is collected using a high bandwidth oscilloscope, by direct probing of a biased reader. Recorded waveforms may contain different noise signals, but free layer FMR is usually a dominating one. The autocorrelation function is a reflection of the damped oscillation curve, averaging out stochastic contributions. The damped oscillator formula is fitted to autocorrelation data, producing resonance frequency and damping constant values. Restricting lag range allows for mitigation of the impact of other phenomena (e.g., reader instability) on the damping constant. For a micromagnetically modeled reader, the technique proves to be much more accurate than the stochastic FMR line width approach. Application to actual reader waveforms yields a damping constant of ∼0.03.

Can a healthy youth development clinic serving latino families be youth friendly and family oriented? A mixed-methods evaluation

It is common to model recording media as interacting coherently rotating magnetic moments, but real materials frequently exhibit perpendicular switching fields less than the anisotropy field and a different angular dependence than theoretically expected. Micromagnetic simulations were performed, which included multiple elements per grain and magnetostatic interactions between elements. Two likely explanations have emerged from this analysis: the existence of low anisotropy regions within the first few atomic layers of the sputtered film or anisotropy gradation throughout the grain thickness. Both explanations offer appropriate coercivity reductions; however, grains including anisotropy gradation display this effect at more realistic values of intragranular exchange. A simplified two element model was fit to the multidomain angle-dependent results in order to find a computationally simple description that can be easily included in a recording simulation.