Europium cyclooctatetraene nanowire carpets: A low-dimensional, organometallic, and ferromagnetic insulator

We investigate the magnetic and electronic properties of europium cyclooctatetraene (EuCot) nanowires by means of low-temperature X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as an insulator with a minority band gap of 2.3 eV. By means of Eu M5,4 edge XMCD, orbital and spin magnetic moments of (−0.1 ± 0.3)μB and (+7.0 ± 0.6)μB, respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M5 edge show hysteresis for grazing X-ray incidence at 5 K, thus confirming EuCot as a ferromagnetic material. Our density functional theory calculations reproduce the experimentally observed minority band gap. Modeling the experimental results theoretically, we find that the effective interatomic exchange interaction between Eu atoms is on the order of millielectronvolts, that magnetocrystalline anisotropy energy is roughly half as big, and that dipolar energy is approximately ten times lower

Influence of non-local damping on magnon properties of ferromagnets

We study the influence of non-local damping on magnon properties of Fe, Co, Ni and Fe$_{1-x}$Co$_{x}$ ($x=30\%,50\%$) alloys. The Gilbert damping parameter is typically considered as a local scalar both in experiment and in theoretical modelling. However, recent works have revealed that Gilbert damping is a non-local quantity that allows for energy dissipation between atomic sites. With the Gilbert damping parameters calculated from a state-of-the-art real-space electronic structure method, magnon lifetimes are evaluated from spin dynamics and linear response, where a good agreement is found between these two methods. It is found that non-local damping affects the magnon lifetimes in different ways depending on the system. Specifically, we find that in Fe, Co, and Ni the non-local damping decreases the magnon lifetimes, while in $\rm Fe_{70}Co_{30}$ and Fe$_{50}$Co$_{50}$ an opposite, non-local damping effect is observed, and our data show that it is much stronger in the former

Tunable and robust room-temperature magnon-magnon entanglement

Although challenging, realizing controllable high-temperature entanglement is of immense importance for practical applications as well as for fundamental research in quantum technologies. Here, we report the existence of entangled steady states in bipartite quantum magnonic systems at high temperatures. We consider dissipative dynamics of two magnons in a bipartite antiferromagnet or ferrimagnet subjected to a vibrational phonon mode and an external rotating magnetic field. To quantify the bipartite magnon-magnon entanglement, we use the entanglement negativity and compute its dependence on the temperature and magnetic field. We show that, for any given phonon frequency and magnon-phonon coupling rates, there are always ranges of the magnetic field amplitudes and frequencies, for which bipartite magnon-magnon entanglement persists up to and above the room temperature. The generality of the result allows for experimental observation in a variety of crystals and synthetic bipartite antiferromagnetic and ferrimagnetic materials.Comment: 6 pages, 5 figure