Separation of magnetic properties at uranium and cobalt sites in UCoAl using soft x-ray magnetic circular dichroism

Yukiharu Takeda,Tatsuma D Matsuda,Etsuji Yamamoto,Yoshichika Ōnuki,Zachary Fisk,Yuji Saitoh,Tetsuo Okane,Yoshinori Haga,Hiroshi Yamagami

doi:10.1103/physrevb.88.075108

Abstract

Temperature ($T$) and magnetic field ($H$) dependence of the magnetic properties in metamagnetic UCoAl have been investigated using a soft x-ray magnetic circular dichroism (XMCD). In order to extract element-specific magnetic properties at the U and Co sites, the XMCD experiment has been performed at the U 4$d$-5$f$ (${N}_{4},5$) and Co 2$p$-3$d$ (${L}_{2},3$) absorption edges, respectively. Directions of magnetic moments at the U and Co sites have been determined from shapes of the XMCD spectra. The directions of the total magnetic moments at the U and Co sites are parallel to the $H$ direction ($c$ axis), but the direction of the spin magnetic moment at the U site is opposite to that at the Co site. The XMCD intensities at both the U and Co sites at $T=5.5$ K increase steeply at $H=0.77$ T (${H}_{\mathrm{m}}$), corresponding to the metamagnetic transition. The XMCD intensities do not saturate, even in the field-induced ferromagnetic state above ${H}_{\mathrm{m}}$. In addition, the ratio of the increase of the XMCD intensity at the Co site is smaller than that at the U site. From comparison of the $H$ dependence of the XMCD intensities at $T=25$ and 5.5 K, we found that the magnetic behavior of the Co atom has a stronger $T$ dependence than that of the U atom.

Highlights

Uranium compounds display unique and interesting properties, for example, showing a coexistence of superconductivity and magnetism derived from the interaction between the U 5f and other ligand electrons.1 Among the uranium compounds, ternary compounds UTAl (T = Co, Rh and Pt) with hexagonal ZrNiAl-type structure exhibit ferromagnetic ordering
The two pairs of the spin-orbit splitting exist in the photon energy region, namely, the U N4,5 and Co L2,3 edges, only three peaks are observed in the x-ray magnetic circular dichroism (XMCD) spectrum due to the spectra at the Co L3 and U N4 edges overlapping around hν = 778 eV
We have performed the element-specific investigation of the magnetic properties in metamagnetic UCoAl via the XMCD experiment at the U N4,5 and the Co L2,3 edges

Summary

INTRODUCTION

The magnetic behavior of UCoAl, which shows the field-induced ferromagnetic state from the paramagnetic state and unsaturated magnetic moment even at high magnetic fields, is similar to that seen in the itinerant 3d-electron systems YCo2 and LuCo2.12,13 it is important to determine the contribution of the Co atom to the metamagnetism given the Co atom common in these materials. Using soft x-rays, the magnetic properties at both the U and Co sites can be simultaneously investigated in the same experiment only by tuning the photon energy to each absorption edge. As for the magnetic properties of the U 5f electrons of UCoAl, 3.0 the H -dependent XMCD experiments at the U 3d-5f (M4,5) absorption edge have already been carried out in the hard x-ray.

EXPERIMENT

RESULTS AND DISCUSSION

SUMMARY