Pd nanoparticle embedded with only one Co atom behaves as a single-particle magnet

Single molecular magnets and single-particle magnets have been intensively investigated from the viewpoints of spintronics devices. We employ the giant magnetic moment effect on magnetic impurities embedded in Pd in designing a single-nanoparticle magnet. A transition metal magnetic impurity such as Co has a giant magnetic moment in Pd metal due to the exchange enhancement effect. As the interaction range of the effect is ca. 1 nm from the magnetic impurity center, all Pd atoms are spin-polarized in a Pd nanoparticle having a radius smaller than the range. Here, we unveil this feature experimentally and show that a Pd nanoparticle containing only one Co atom exhibits a single-domain nanomagnet behavior with a blocking temperature of 3K.