# Leveraging 3d‐4f Coordination: Molecular Quantum Spring‐Magnet Behavior in Axial Ni2Ln Complexes

## TL;DR

Scientists created molecular magnets using Ni and lanthanide ions that mimic the behavior of larger magnets, showing potential for quantum and nanoscale devices.

## Contribution

The study introduces a new class of molecular magnets with tunable bistability through 3d–4f coordination and anisotropy alignment.

## Key findings

- Ni2Tb, Ni2Dy, and Ni2Ho complexes show slow magnetic relaxation and open hysteresis loops.
- Ferromagnetic coupling between Ni and lanthanide ions enhances magnetic bistability.
- Collinear anisotropy axes and electronic configurations are favorable for magnetic performance.

## Abstract

We report heterotrimetallic 3d–4f complexes, mimicking classical exchange spring magnets at the molecular scale. The complexes feature a linear Ni···Ln···Ni core, where the lanthanide ion is sandwiched between two Ni2+ centers coordinated by N3O3 ligand environments. The complexes are isostructural, while CASSCF calculations reveal collinear anisotropy axes and favorable electronic configurations for magnetic bistability in selected systems. Magnetic characterization via DC, AC, and µSQUID magnetometry down to 30 mK demonstrates slow magnetic relaxation and open hysteresis loops exclusively in Ni2Tb, Ni2Dy, and Ni2Ho. These systems exhibit ferromagnetic 3d‐4f coupling, while their isolated or antiferromagnetically coupled analogs (Ni2Y, Zn2Tb/Dy) and Ni2Er/Yb counterparts show fast relaxation and closed loops. Analysis suggests that the Ni2+ ions alone, with modest anisotropy, deviate from the expected “hard” magnetic behavior due to a broad zero‐field QTM, while the Ln3+ ions alone serve as the “soft” phase with large magnetic moments and sharp zero‐field QTM. Nevertheless, when brought together, their coupling and alignment of the anisotropy axis enhances the magnetic performance with exchange‐bias features mimicking the macroscopic exchange spring magnets. We highlight an optimal utilization of 3d‐4f coordination in designing molecular magnets with tunable relaxation and bistability, advancing prospects for quantum information and nanoscale magnetic devices.

We report heterotrimetallic Ni2Ln complexes mimicking exchange spring magnets at the molecular level. CASSCF calculations show collinear anisotropy axes, while µSQUID studies reveal slow relaxation and open hysteresis in Ni2Tb, Ni2Dy, and Ni2Ho. Ferromagnetic 3d–4f coupling and anisotropy alignment enhance bistability, offering promise for quantum, and nanoscale magnetic devices.