Experimental Observation of Long-Range Magnetic Order in Icosahedral Quasicrystals

Abstract

<p class="first" id="d2685151e310"> <div class="figure-container so-text-align-c"> <img alt="" class="figure" src="/document_file/9c642948-ab54-493e-a85b-1693f45ca370/PubMedCentral/image/ja1c09954_0006"/> </div> </p><p id="d2685151e312">Quasicrystals (QCs), first discovered in 1984, generally do not exhibit long-range magnetic order. Here, we report on long-range magnetic order in the real icosahedral quasicrystals ( <i>i</i> QCs) Au–Ga–Gd and Au–Ga–Tb. The Au ₆₅Ga ₂₀Gd ₁₅ <i>i</i> QC exhibits a ferromagnetic transition at <i>T</i> _C = 23 K, manifested as a sharp anomaly in both magnetic susceptibility and specific heat measurements, along with an appearance of magnetic Bragg peak below <i>T</i> _C. This is the first observation of long-range magnetic order in a real quasicrystal, in contrast to the spin-glass-like behaviors observed for the other magnetic quasicrystals found to date. Moreover, when Gd is replaced by Tb, i.e., for the Au ₆₅Ga ₂₀Tb ₁₅ <i>i</i> QC, a ferromagnetic behavior is still retained with <i>T</i> _C = 16 K. Although the sharp anomaly in the specific heat observed for the Au ₆₅Ga ₂₀Gd ₁₅ <i>i</i> QC becomes broadened upon Tb substitution, neutron diffraction experiments clearly show marked development of magnetic Bragg peaks just below <i>T</i> _C, indicating long-range magnetic order for the Au ₆₅Ga ₂₀Tb ₁₅ <i>i</i> QC also. Our findings can contribute to the further investigation of exotic magnetic orders formed on real quasiperiodic lattices with <i>unprecedented</i> highest global symmetry, i.e., icosahedral symmetry. </p>