# Low-temperature anomalies in muon spin relaxation of solid and hollow nanoparticles: a pathway to detect unusual local spin dynamics

Basini, M.; Sanna, S.; Orlando, T.; Bordonali, L.; Cobianchi, M.; Arosio, P.; Mariani, M.; Peddis, D.; Bonanni, V.; Mathieu, R.; Kalaivani, T.; Singh, G.; Larionova, J.; Guari, Y.; Lartigue, L.; Lascialfari, A.

##### Abstract:
By means of muon spin relaxation measurements we unraveled the temperature spin dynamics in monodisperse maghemite spherical nanoparticles with different surface to volume ratio, in two samples with a full core (diameter D∼4 and D∼5nm) and one with a hollow core (external diameter D∼7.4nm). The behavior of the muon longitudinal relaxation rates as a function of temperature allowed us to identify two distinct spin dynamics. The first is well witnessed by the presence of a characteristic peak for all the samples around the so-called muon blocking temperature T$_{B}^{μ+}$. A Bloembergen-Purcell-Pound (BPP)-like model reproduces the experimental data around the peak and at higher temperatures (20<T<100K) by assuming the Néel reversal time of the magnetization as the dominating correlation time. An additional dynamic emerges in the samples with higher surface to volume ratio, namely, full 4 nm and hollow samples. This is witnessed by a shoulder of the main peak for T<20K at low longitudinal field (μ$_{0}$H≈15mT), followed by an abrupt increase of the relaxation rate at T<10K, which is more evident for the hollow sample. These unusual anomalies of the longitudinal relaxation rate for T<T$_{B}^{μ+}$ are suggested to be due to the surface spins’ dynamical behavior. ... mehr

 Zugehörige Institution(en) am KIT Institut für Mikrostrukturtechnik (IMT) Publikationstyp Zeitschriftenaufsatz Publikationsjahr 2020 Sprache Englisch Identifikator ISSN: 2469-9950, 2469-9969 KITopen-ID: 1000126977 HGF-Programm 43.22.03 (POF III, LK 01) Printed Materials and Systems Erschienen in Physical review / B Verlag American Physical Society (APS) Band 102 Heft 19 Seiten Art.Nr. 195424 Vorab online veröffentlicht am 19.11.2020 Nachgewiesen in Web of ScienceDimensionsScopus
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