# Delving into the Correlation between Magnetic and Lattice Degrees of Freedom from Magnetocaloric and Magnetovolume Effects in Lu2Fe17 Ribbons

## TL;DR

This study explores how magnetic and structural properties interact in Lu2Fe17 ribbons, revealing two magnetic phase transitions and unusual thermal expansion behaviors.

## Contribution

The paper provides new insights into the magnetovolume and magnetocaloric effects in Lu2Fe17 ribbons through structural and magnetic analysis.

## Key findings

- Lu2Fe17 ribbons exhibit negative and zero thermal expansion along different crystallographic axes.
- Two magnetic phase transitions were identified in the ribbons, with distinct transition temperatures compared to bulk samples.
- The isothermal entropy change curves show a double peak, confirming the two magnetic transitions.

## Abstract

Nowadays, R2Fe17 (R = rare earth)
materials
with zero (ZTE) or negative (NTE) thermal expansion are of significant
interest in advanced applications, especially for intermediate performance
low-cost magnets. Lu2Fe17 ribbon flakes were
fabricated by means of the melt-spinning technique, while a bulk sample
was synthesized by arc melting and long-term annealing as a reference
alloy. Both the as-cast ribbons and the bulk sample adopt a Th2Ni17-type hexagonal crystal structure. The anomalous
temperature dependence of the lattice parameters in the ribbons confirms
the existence of strong magnetovolume effects, characterized by NTE
and ZTE along the c and a crystallographic
axis, respectively. In addition, magnetic measurements show two magnetic
phase transitions, from paramagnetic to helimagnetic and from helimagnetic
to a fan structure, with transition temperatures differing between
ribbon (T
HEL = 276 K and T
FAN = 252 K) and bulk (273 and 257 K) samples, respectively.
These differences can be attributed to variations in the exchange
interactions caused by slightly different interatomic distances between
the Fe atoms. The isothermal entropy change versus temperature curves,
ΔS
M(T), measured
under low magnetic field values (up to 150 mT), provide clear evidence
of the existence of a double peak, thus confirming the two successive
magnetic phase transitions that occur in Lu2Fe17 ribbon flakes.