Novel family of near-room-temperature compensated itinerant pyrochlore ferrimagnets, $R{\mathrm{In}}{\mathrm{Co}}_{4}$ ($R=$ Dy-Tm)

TL;DR

The authors synthesize single crystals of the cubic C15b Laves-phase series $R\mathrm{InCo_4}$ ($R=\mathrm{Dy}$–$\mathrm{Tm}$) consisting of Co-pyrochlore and $R$-fcc sublattices and show that these itinerant magnets exhibit compensated ferrimagnetism with Curie temperatures above room temperature and compensation points near room temperature, whose exact values depend on the $R$ ion via the de Gennes factor. Through X-ray diffraction and magnetization studies, they establish a predominantly collinear ferrimagnetic arrangement at low temperatures with well-defined easy axes ($[001]$ for Dy, $[111]$ for Er, $[110]$ for Tm) and more complex behavior for Ho, and they observe a secondary low-temperature anomaly suggesting spin reorientation or lattice distortions. High-temperature ordering is governed by the Co sublattice, while the $R$ sublattice determines anisotropy and compensation, highlighting a robust platform for tunable spintronic materials. The combination of a high $T_{ m C}$ and a near-room-temperature $T_{ m cp}$, together with tunable anisotropy and potential lattice coupling, points to practical relevance for spintronics and magnetocaloric applications in itinerant pyrochlore magnets.

Abstract

We successfully synthesized single crystals of a series of C15b Laves phase compounds, $R{\mathrm{In}}{\mathrm{Co}}_{4}$ ($R=$ Dy-Tm), with Co-pyrochlore and $R$-fcc sublattices, and systematically studied their magnetic properties via magnetometry measurements. These itinerant cubic compounds, with Curie temperatures above room temperature, show compensated ferrimagnetism featuring an antiferromagnetic coupling between the two sublattices. From this series, ${\mathrm{DyInCo}}_{4}$ exhibits the highest $T_{\rm C}$ (= 368 K) and a near-room-temperature compensation point $T_{\rm cp}$ (= 295 K). $T_{\rm C}$ does not change drastically with the $R$ atom, whereas $T_{\rm cp}$ depends on the de Gennes factor of $R^{3+}$. Another magnetization anomaly is observed in all the compounds at low temperatures, which may be indicative of changes in the lattice or magnetic structure. The easy axis the ferrimagnetic moment of ${\mathrm{DyInCo}}_{4}$, ${\mathrm{ErInCo}}_{4}$, and ${\mathrm{TmInCo}}_{4}$ is found at $T =$ 5 K to be along the [001], [111] and [110] directions, respectively. However, the simple easy-axis or easy-plane ferrimagnetic picture cannot be applied to ${\mathrm{HoInCo}}_{4}$. These observations suggest that the $R$ sublattice determines magnetic anisotropy and compensation, while the Co sublattice plays a role in strong magnetic ordering. The high Curie temperature, together with the magnetization compensation point near room temperature, renders these itinerant pyrochlore magnets interesting for spintronic applications.

Figures (6)

• Figure 1: Crystal structures of the C15 and C15b Laves phase compounds.
• Figure 2: (a) Powder XRD profiles of $R$InCo_4 at room temperature. (b) Profiles in the extended $2\theta$ range, where the 200 superstructure peak is observed. The inset shows the lattice parameter as a function of the $R$-atomic number. LuInCo_4 data were taken from to our previous report LIC.
• Figure 3: Temperature dependence of the magnetization of $R$InCo_4 ($R$ = Dy--Tm) at (a)--(d) $H=100$ Oe and (e)--(h) $H=1$ kOe. Dark and light markers represent data obtained under field-cooled and zero-field-cooled conditions, respectively. (i) data across the magnetization anomaly at $T^*$. A field of $H = 100$ Oe was applied in the [001] direction for $R$ = Dy and in the [111] direction for $R$ = Ho--Tm.
• Figure 4: Curie and compensation temperatures as a function of the de Gennes factor, $\xi$. Data of LuInCo_4, YbInCo_4, and $R$Co_2 were taken from Ref. LIC, tsujii, and RCTC, respectively. Lines are guides to the eye.
• Figure 5: The inverse susceptibility of $R$InCo_4. The solid curves represent the fit to the Eq. \ref{['Neel']}.