Temperature dependence of ESR intensity for the nanoscale molecular magnet V15

TL;DR

This study investigates the temperature dependence of ESR intensity in nanoscale V15 magnetic molecules, employing advanced numerical methods to match experimental data and reveal side peaks caused by Dzyaloshinsky-Moriya interactions.

Contribution

It introduces the double Chebyshev expansion method for ESR calculations in large Hilbert spaces and compares it with a low-lying state subspace approach.

Findings

Side peaks in ESR appear due to Dzyaloshinsky-Moriya interaction.

ESR intensity varies with temperature, showing growth of side peaks at lower temperatures.

The methods successfully reproduce experimental ESR features below 100 K.

Abstract

The electron spin resonance (ESR) of nanoscale molecular magnet ${\rm V}_{15}$ is studied. Since the Hamiltonian of ${\rm V}_{15}$ has a large Hilbert space and numerical calculations of the ESR signal evaluating the Kubo formula with exact diagonalization method is difficult, we implement the formula with the help of the random vector technique and the Chebyshev polynominal expansion, which we name the double Chebyshev expansion method. We calculate the temperature dependence of the ESR intensity of ${\rm V}_{15}$ and compare it with the data obtained in experiment. As another complementary approach, we also implement the Kubo formula with the subspace iteration method taking only important low-lying states into account. We study the ESR absorption curve below $100{\rm K}$ by means of both methods. We find that side peaks appear due to the Dzyaloshinsky-Moriya interaction and these peaks grows as temperature decreases.