Amorphous ferromagnetism and re-entrant magnetic glassiness in Sm${}_2$Mo${}_2$O${}_7$: new insights into the electronic phase diagram of pyrochlore molybdates

Abstract

We discuss the magnetic properties of a Sm${}_2$Mo${}_2$O${}_7$ single crystal as investigated by means of different experimental techniques. In the literature, a conventional itinerant ferromagnetic state is reported for the Mo${}^{4+}$ sublattice below $\sim 78$ K. However, our results of dc magnetometry, muon spin spectroscopy (${\mu }^{+}$SR) and high-harmonics magnetic ac susceptibility unambiguously evidence highly disordered conditions in this phase, in spite of the crystalline and chemical order. This disordered magnetic state shares several common features with amorphous ferromagnetic alloys. This scenario for Sm${}_2$Mo${}_2$O${}_7$ is supported by the anomalously high values of the critical exponents, as mainly deduced by a scaling analysis of our dc magnetization data and confirmed by the other techniques. Moreover, ${\mu }^{+}$SR detects a significant static magnetic disorder at the microscopic scale. At the same time, the critical divergence of the third-harmonic component of the ac magnetic susceptibility around $\sim 78$ K leads to additional evidence towards the glassy nature of this magnetic phase. Finally, the longitudinal relaxation of ${\mu }^{+}$ spin polarization (also supported by results of ac susceptibility) evidences re-entrant glassy features similar to amorphous ferromagnets.

15 pages, 13 figures

References in corpus (15)

• Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7
• Magnetic Order in the Pyrochlore Iridates A2Ir2O7 (A = Y, Yb)
• Brownian Motion and Quantum Dynamics of Magnetic Monopoles in Spin Ice
• Direct Evidence for the 'All-in/All-out' Magnetic Structure in the Pyrochlore Iridates from $\mu$SR
• Formation of finite antiferromagnetic clusters and the effect of electronic phase separation in Pr{_0.5}Ca{_0.5}Mn{_0.975}Al{_0.025}O{_3}
• Magnetic order, magnetic correlations and spin dynamics in the pyrochlore antiferromagnet Er2Ti2O7
• Non-monotonic zero point entropy in diluted spin ice
• Ordering of the pyrochlore Ising model with the long-range RKKY interaction
• Probing a ferromagnetic critical regime using nonlinear susceptibility
• Common effect of chemical and external pressures on the magnetic properties of RECoPO (RE = La, Pr)
• Phase competition in the double-exchange model on the frustrated pyrochlore lattice
• Unconventional critical scaling of magnetization in uranium ferromagnetic superconductors UGe${}_2$ and URhGe
• Ordered spin-ice state in the geometrically frustrated metallic-ferromagnet Sm2Mo2O7
• Origin of magnetic freezing in the pyrochlore Y2Mo2O7
• Single-crystal growth and magnetic properties of the metallic molybdate pyrochlore Sm2Mo2O7