# Cation Exchange as a Route to Introduce Magnetism to Hybrid-Improper Polar Phases

## TL;DR

This paper explores how cation exchange can introduce magnetism to a specific type of polar crystal structure, resulting in new magnetic properties in modified materials.

## Contribution

The study introduces magnetism into hybrid-improper polar phases through cation exchange, revealing distinct magnetic behaviors in different transition-metal compounds.

## Key findings

- FeCaTa2O7 and CoCaTa2O7 exhibit antiferromagnetic ordering at specific Néel temperatures.
- The magnetic state of FeCaTa2O7 shows a glassy component at low temperatures.
- ZnCaTa2O7 adopts a different polar structure compared to FeCaTa2O7 and CoCaTa2O7.

## Abstract

The pseudo Ruddlesden–Popper phase Li2CaTa2O7 is converted to ZnCaTa2O7, FeCaTa2O7, or CoCaTa2O7 by reaction with the corresponding transition-metal dichloride.
Diffraction data reveal that ZnCaTa2O7 adopts
a polar crystal structure (P2cm)
with the Zn2+cations ordered into stripes within the interlayer
coordination sites, and the TaO6 units adopt an a
–
b
–
c
+/–(a
–
b
–)c
+ tilting pattern. In contrast, FeCaTa2O7 and
CoCaTa2O7 adopt polar structures (P21
nm) with the transition-metal cations
ordered in a checkerboard pattern within the interlayer coordination
sites, and the TaO6 units adopt an a
–
b
–
c
+/ b
–
a
–
c
+ tilting pattern.
The different polar structures adopted are rationalized on the basis
of the size of the interlayer transition-metal cation. On cooling,
FeCaTa2O7 (T
N =
40 K) and CoCaTa2O7 (T
N = 25 K) adopt antiferromagnetically ordered states with spins
aligned parallel to the crystallographic stacking axis and arranged
in a G-type manner. Close inspection of the NPD data collected from
FeCaTa2O7 at low temperature reveals a diffuse
component to the magnetic scattering, which, in combination with magnetization
data, suggest a glassy component to the low-temperature magnetic state.
Neither FeCaTa2O7 nor CoCaTa2O7 shows significant lattice parameter anomalies around their
respective Néel temperatures, in contrast to the previously
reported manganese analogue MnCaTa2O7.