arXiv subjects

Sidhartha Patnaik

Publications and source records attributed to Sidhartha Patnaik.

4 recordsLinked to original sources

arXiv2025

Time Optimal Control Problem for the Landau-Lifshitz-Bloch equation

This paper investigates the time-optimal control problem for the Landau-Lifshitz-Bloch (LLB) equation, a macroscopic model that characterizes magnetization dynamics in ferromagnetic materials across a wide temperature range, including near and above the Curie temperature. We analyze the LLB system on bounded domains in one, two, and three dimensions, establishing the existence of optimal controls that drive the magnetization to a desired target state within a minimal time frame. Utilizing a Lagrange multiplier approach and an adjoint-based framework, we derive first-order necessary optimality conditions. Furthermore, we establish second-order sufficient conditions for local optimality, addressing the mathematical challenges posed by the system's inherent nonlinearities and the nonlinear appearance of the control in the effective magnetic field. These results provide a rigorous theoretical basis for the rapid manipulation of magnetic states, offering insights into the fundamental limits of control for nonlinear diffusion-relaxation processes in magnetism. Such findings are essential for advancing high-speed magnetic memory technologies and optimizing thermal magnetic switching in next-generation storage technologies.

math.OC↗

arXiv2025

Magnetization control problem for the 2D and 3D evolutionary Landau-Lifshitz-Bloch equation

In this study, we investigate the optimal control of the Landau-Lifshitz-Bloch equation within confined domains in $\mathbb R^n$ for $n= 2, 3.$ We establish the existence of strong solutions for dimensions $n=1, 2, 3$ under suitable growth conditions on the control, and analyze the existence and uniqueness of regular solutions. We formulate the control problem in which only a fixed set of finite magnetic field coils can constitute the external magnetic field (control). We define a cost functional by aiming at minimizing the energy discrepancy between the evolving magnetic moment and the desired state. We demonstrate the existence of an optimal solution pair and employ the classical adjoint problem approach to derive a first-order necessary optimality condition. Given the non-convex nature of the optimal control problem, we derive a second-order sufficient optimality condition using a cone of critical directions. Finally, we prove two crucial results, namely, a global optimality condition and uniqueness of an optimal control.

math.OC↗

arXiv2023

Analysis of the magnetization control problem for the 2D evolutionary Landau-Lifshitz-Gilbert equation

The magnetization control problem for the Landau-Lifshitz-Gilbert (LLG) equation $m_t= m \times (Δm +u)- m \times (m \times (Δm +u)),\ (x,t) \in Ω\times (0,T] $ with zero Neumann boundary data on a two-dimensional bounded domain $Ω$ is studied when the control energy $u$ is applied on the effective field. First, we show the existence of a weak solution, and the magnetization vector field $m$ satisfies an energy inequality. If a weak solution $m$ obeys the condition that $\nabla m\in L^4(0,T;L^4(Ω)),$ then we show that it is a regular solution. The classical cost functional is modified by incorporating $L^4(0,T;L^4(Ω))$-norm of $\nabla m$ so that a rigorous study of the optimal control problem is established. Then, we justified the existence of an optimal control and derived first-order necessary optimality conditions using an adjoint problem approach. We have established the continuous dependency and Fréchet differentiability of the control-to-state and control-to-costate operators and shown the Lipschitz continuity of their Fréchet derivatives. Using these postulates, we derived a local second-order sufficient optimality condition when a control belongs to a critical cone. Finally, we also obtain another remarkable global optimality condition posed only in terms of the adjoint state associated with the control problem.

math.OC↗

arXiv2023

Optimal Control of the 2D Landau-Lifshitz-Gilbert Equation with Control Energy in Effective Magnetic Field

The optimal control of magnetization dynamics in a ferromagnetic sample at a microscopic scale is studied. The dynamics of this model is governed by the Landau-Lifshitz-Gilbert equation on a two-dimensional bounded domain with the external magnetic field (the control) applied through the effective field. We prove the global existence and uniqueness of a regular solution in $\mathbb S^2$ under a smallness condition on control and initial data. We establish the existence of optimal control and derive a first-order necessary optimality condition using the Fréchet derivative of the control-to-state operator and adjoint problem approach.

math.OC↗