Colossal stability of antiferromagnetically exchange coupled nanomagnets.

Bistable nanomagnets store a binary bit of information. Exchange coupled nanomagnets can increase the thermal stability at low dimensions. Here we show that the antiferromagnetically (AFM) coupled nanomagnets can be highly stable at low dimensions than that of the ferromagnetically coupled nanomagnets. By solving stochastic Landau-Lifshitz-Gilbert equation of magnetization dynamics at room temperature, we analyze the stability of the exchange coupled nanomagnets in the presence of correlated, uncorrelated, and anti-correlated noise. The results show that the correlated noise can make the stability of the AFM coupled nanomagnets very high. Such finding will lead to very high-density non-volatile storage and logic devices in our future information processing systems.

Red blood cell indices in different hemoglobinopathies: A cross-sectional study in Eastern India.

Introduction: Beta thalassemia and hemoglobin (HbE)-related hemoglobinopathies are common public health problems in developing countries. High-performance liquid chromatography (HPLC) is currently the diagnostic test of choice for carrier detection, but it is costly. Hence, some initial screening and complementary tests are required, which can be affordable. Aims: To find out the distribution of different red blood cell (RBC) indices in beta thalassemia trait (BTT) and HbE-related hemoglobinopathies and to determine their significance as screening tests to distinguish between these hemoglobinopathies. Study Settings and Design: This observational cross-sectional study has been carried out at an NABL (National Accreditation Board for Testing and Calibration Laboratories)-accredited Laboratory of Eastern India with approval from the concerned Institutional Ethics Committee from January 2021 to March 2021. Methods and Material: : HPLC tests and complete hemograms were performed on 2247 ethylenediaminetetraacetic acid anti-coagulated blood samples over 3 months. Patients <1 year of age or having a history of blood transfusion within the past 06 months were excluded. Statistical Analysis: : One-way analysis of variance along with Bonferroni post-hoc test was performed to find out significant differences of means of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), hemoglobin%, red blood cell (RBC) count, and red cell distribution width (RDW-CV) among concerned hemoglobinopathies. Results: The results show a significant difference of total RBC count, RDW, MCV, MCH, and MCHC between BTT and E-trait. No significant difference of mean was found between HbE homozygous and E-beta. E-trait differs from both HbE homozygous and E-beta significantly in three parameters, namely, RDW, MCV and MCH. A value of MCV at ≤73.8 fl and MCH at ≤21.9 pg may be a clue of diagnosis for BTT rather than E-trait with >90% sensitivity and >80% specificity. Conclusion: RBC indices vary significantly between BTT and other HbE-related hemoglobinopathies. They can specially be utilized to differentiate BTT and E-trait as supportive tests in addition to the gold standard test of HPLC.

Magnetization dynamics, Bennett clocking and associated energy dissipation in multiferroic logic.

It has been recently shown that the magnetization of a multiferroic nanomagnet, consisting of a magnetostrictive layer elastically coupled to a piezoelectric layer, can be rotated by a large angle if a tiny voltage of a few tens of millivolts is applied to the piezoelectric layer. The potential generates stress in the magnetostrictive layer and rotates its magnetization by ~90° to implement Bennett clocking in nanomagnetic logic chains. Because of the small voltage needed, this clocking method is far more energy efficient than those that would employ spin transfer torque or magnetic fields to rotate the magnetization. In order to assess if such a clocking scheme can also be reasonably fast, we have studied the magnetization dynamics of a multiferroic logic chain with nearest-neighbor dipole coupling using the Landau-Lifshitz-Gilbert (LLG) equation. We find that clock rates of 2.5 GHz are feasible while still maintaining the exceptionally high energy efficiency. For this clock rate, the energy dissipated per clock cycle per bit flip is ~52,000 kT at room temperature in the clocking circuit for properly designed nanomagnets. Had we used spin transfer torque to clock at the same rate, the energy dissipated per clock cycle per bit flip would have been ~4 x 108 kT, while with current transistor technology we would have expended ~106 kT. For slower clock rates of 1 GHz, stress-based clocking will dissipate only ~200 kT of energy per clock cycle per bit flip, while spin transfer torque would dissipate about 108 kT. This shows that multiferroic nanomagnetic logic, clocked with voltage-generated stress, can emerge as a very attractive technique for computing and signal processing since it can be several orders of magnitude more energy efficient than current technologies.

Separating read and write units in multiferroic devices.

Strain-mediated multiferroic composites, i.e., piezoelectric-magnetostrictive heterostructures, hold profound promise for energy-efficient computing in beyond Moore's law era. While reading a bit of information stored in the magnetostrictive nanomagnets using a magnetic tunnel junction (MTJ), a material selection issue crops up since magnetostrictive materials in general cannot be utilized as the free layer of the MTJ. This is an important issue since we need to achieve a high magnetoresistance for technological applications. We show here that magnetically coupling the magnetostrictive nanomagnet and the free layer e.g., utilizing the magnetic dipole coupling between them can circumvent this issue. By solving stochastic Landau-Lifshitz-Gilbert equation of magnetization dynamics in the presence of room-temperature thermal fluctuations, we show that such design can eventually lead to a superior energy-delay product.

Landauer limit of energy dissipation in a magnetostrictive particle.

According to Landauer's principle, a minimum amount of energy proportional to temperature must be dissipated during the erasure of a classical bit of information compensating the entropy loss, thereby linking the information and thermodynamics. Here, we show that the Landauer limit of energy dissipation is achievable in a shape-anisotropic single-domain magnetostrictive nanomagnet having two mutually anti-parallel degenerate magnetization states that store a bit of information. We model the magnetization dynamics using the stochastic Landau-Lifshitz-Gilbert equation in the presence of thermal fluctuations and show that on average the Landauer bound is satisfied, i.e. it is in accordance with the generalized Landauer's principle for small systems with stochastic fluctuations.

Binary switching in a 'symmetric' potential landscape.

A binary switch is the basic building block for information processing. The potential energy profile of a bistable binary switch is a 'symmetric' double well. The traditional method of switching it from one state (one well) to the other is to tilt the profile towards the desired state. Here, we present a case, where no such tilting is necessary to switch successfully, even in the presence of thermal noise. This happens because of the built-in dynamics inside the switch itself. It differs from the general perception on binary switching that in a 'symmetric' potential landscape, the switching probability is 50% in the presence of thermal noise. Our results, considering the complete three-dimensional potential landscape, demonstrate intriguing phenomena on binary switching mechanism. With experimentally feasible parameters, we theoretically demonstrate such intriguing possibility in electric field induced magnetization switching of a shape-anisotropic single-domain magnetostrictive nanomagnet with two stable states at room-temperature.