# Unusual Magnetic Order in Eu11–x Hg54+x

## TL;DR

This study explores the magnetic properties of a europium-based compound with a complex structure, revealing a unique magnetic order and phase transitions at low temperatures.

## Contribution

The paper identifies a fragile magnetic ground state and unusual magnetic ordering in a noncentrosymmetric europium compound.

## Key findings

- Eu11–x Hg54+x exhibits magnetic ordering below 5.5 K with a spin reorientation at 4.3 K.
- The compound shows a magnetization pole reversal due to a delicate ferrimagnetic ground state.
- Additional magnetic phases can be induced by applying a modest external magnetic field.

## Abstract

In solid-state compounds, the valence of europium can
sometimes
be mixed, which is especially favored in structures with several positions
for the europium atoms. In this work, we study the Eu-based intermetallic
noncentrosymmetric system Eu11–x
Hg54+x
, which has 65 atoms per unit cell
and 4 distinct crystallographic positions for europium and 14 positions
for mercury. Our detailed analysis of the magnetism of large single
crystals suggests that europium in Eu11–x
Hg54+x
might be present in two
valence states, resulting in a fragile magnetic ground state. Due
to the cage-like structure with a large distance between the Eu atoms,
those atoms are weakly ferromagnetically coupled and Eu11–x
Hg54+x
orders at low
temperatures, below T
1 = 5.5 K, with a
subsequent spin reorientation at T
2 =
4.3 K. There is no sign of magnetic frustration. Interestingly, the
magnetic ordering of the europium substructure results in a magnetization
pole reversal with a delicate ferrimagnetic ground state. Additional
magnetic phases can be induced by the application of a modest external
magnetic field.