ABSTRACT
Magnetic damping is a key metric for emerging technologies based on magnetic nanoparticles, such as spin torque memory and high-resolution biomagnetic imaging. Despite its importance, understanding of magnetic dissipation in nanoscale ferromagnets remains elusive, and the damping is often treated as a phenomenological constant. Here, we report the discovery of a giant frequency-dependent nonlinear damping that strongly alters the response of a nanoscale ferromagnet to spin torque and microwave magnetic field. This damping mechanism originates from three-magnon scattering that is strongly enhanced by geometric confinement of magnons in the nanomagnet. We show that the giant nonlinear damping can invert the effect of spin torque on a nanomagnet, leading to an unexpected current-induced enhancement of damping by an antidamping torque. Our work advances the understanding of magnetic dynamics in nanoscale ferromagnets and spin torque devices.
ABSTRACT
The magnetization dynamics of nano-oscillators may be excited by both magnetic fields and spin-polarized currents. While the dynamics of single oscillators has been well characterized, the synchronization of several ones is not fully understood yet. An analytical and numerical study of the nonlinear dynamics of two magnetostatically coupled spin valves driven by spin-transfer torques is presented under the macrospin approximation. The oscillators interact via magnetostatic fields and exhibit a robust synchronized magnetization motion. We describe the magnetization dynamics of the system using the Landau-Lifshitz-Gilbert-Slonczewski equation. Using a modal decomposition technique, we describe the dynamics, synchronization, and competition of oscillatory modes as a function of the current density, and the geometrical parameters of the setup. Simulations of the Landau-Lifshitz-Gilbert-Slonczewski equation show good agreement with an approximate analytic solution.
ABSTRACT
The essay discusses abortion in Puerto Rico from 1937 to 1970, concentrating in its legal status as well as its social practice. The research documents the contradictions between the legality of the procedure and a social practice characterized by secrecy. The essay discusses the role of the Clergy Consultation Service on Abortion in promoting the legal practice of absortion in Puerto Rico. It also discusses the ambivalent role of medical doctors who, despite being legally authorized to perform abortions to protect the life and health of women, refused to perform the procedure arguing abortion was illegal. The essay concludes with a brief discussion on perceptions of illegality regarding abortion, emphasizing the contradictions between the practice of abortion and that of sterilization in Puerto Rico.
PIP: The legal status and occurrence of abortion in Puerto Rico are examined for the years from 1937 (when abortion under some conditions was legalized) through 1970. A series of legislative initiatives in 1937 repealed laws prohibiting interstate transportation of contraceptive materials and information, legalized contraceptive sterilization, and permitted abortion to conserve the health or life of the woman. The effective legalization of abortion in 1937 was not publicly recognized at the time or in later decades, and the legal changes apparently did not lead immediately to a significant increase in the number of abortions, unlike sterilizations, which did increase significantly. The requirement that indications for therapeutic abortion be identified by physicians excluded the nurses and midwives who had traditionally been responsible for most births and abortions. Foreign organizations such as the Clergy Consultation Service promoted the legal practice of abortion in Puerto Rico. Efforts in 1964 to amend the penal code to curtail abortion were less successful than the passage by New York in 1970 of the most liberal abortion law in the US, which greatly reduced the number of abortions in Puerto Rico. Puerto Rican women able to pay obtained abortions from trained professionals, despite the perception of abortion as illegal, but poor women had recourse to poorly trained midwives and nurses at best. A training program for midwives during the 1930s provided instruction and equipment necessary for safe deliveries, but the knowledge gained was reflected in safer abortions and declining maternal mortality.