Novel dynamical magnetic properties in the spin ice compound Dy₂Ti₂O₇

Abstract

We found two distinct maxima in the ac magnetic susceptibility χac of dysprosium titanate pyrochlore Dy2Ti2O7. Their different frequency dependence of χac suggest the existence of two different types of dynamical behaviour. One of them, observed below 2 K is the relaxation becoming very slow at lower temperature T, possibly related to a highly degenerate ground state (`spin ice' state). Another slowing down phenomenon is evident above ~10 K. Surprisingly, however, there is no anomaly in the dc magnetic susceptibility at this temperature range. Analysing the frequency dependence of χac, we found that in spite of a structurally ordered system the magnetic relaxation is well expressed by a Davidson-Cole formula, which is characterized by a wide distribution of the relaxation time τ to the short-τ region and a temperature dependent cut-off, τc, in the slow relaxations. The magnetic relaxation of the spin ice compound Dy2Ti2O7 is uniquely in contrast with known slow dynamics.

Evidence of impurity and boundary effects on magnetic monopole dynamics in spin ice

“…The motion of magnetic monopoles has been observed experimentally through the generation of monopole currents by the application of a magnetic field 7 , and muon spin rotation 8 , which is a subject of recent controversy 9 . Monte Carlo simulations of a Coulomb gas of monopoles 10 and the dipolar spin-ice model 11 , equation (1), agree well with experimental results down to 1 K, below which the observed dynamics become much slower in the experiments than in the simulations [11][12][13][14][15][16][17] . In this study we find that significant corrections to the ideal model in equation (1) are necessary to accurately model the motion of magnetic monopoles in the real material.…”

Dirty spin ice: The effect of dilution on spin freezing inDy2Ti2OSnyder1, Slusky2, Cava3 et al. 2002Phys. Rev. B484330View full textAdd to dashboardCite

“…Since the spin-spin correlations in SCGO are also fairly short-range [36,37], the distinction appears that in Dy 2 Ti 2 O 7 , the freezing at T f represents the development of only nearest-neighbor correlations, and that longer range freezing occurs entirely at a lower temperature -presumably T ~ 2K where the entropy is observed to freeze out. the freezing in the heat capacity and the fact that no anomaly is seen above 2 K in the d.c.susceptibility [ 9]. Since dilution affects the T ~ 16 K feature, we believe that feature cannot correspond to a single ion effect, but must be also associated with the development of spin-spin correlations and therefore is a precursor to the lower temperature "spin ice" freezing of the entropy.…”

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ABSTRACTWe have studied spin freezing in the diluted spin ice compound Although geometrical magnetic frustration has been most extensively studied in materials with antiferromagnetic nearest-neighbor interactions, the effects of strong frustration have also been found in the so-called "spin ice" materials (such as Dy 2 Ti 2 O 7 , Ho 2 Ti 2 O 7 , and Ho 2 Sn 2 O 7 ) [ 3,4,5,6,7,8,9,10,11,12] in which ferromagnetic and dipolar interactions can be frustrated [13,14,15,16]. The spins in these compounds are governed by the same statistical mechanics as the hydrogen atoms in the ground state of ordinary hexagonal ice (Ih) [17,18,19].

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Magnetothermal study of a Dy-stuffed spin ice:Dy2(DyxTi2−x)Ueland1, Lau2, Freitas3 et al. 2008Phys. Rev. B16140View full textAdd to dashboardCite

“…The energy scales of the interactions in these magnets offer unique opportunities to study how frustrated thermodynamic systems settle into their lowest energy states [1,2,3]. Examples of novel ground states observed in geometrically frustrated magnets include spin-glass-like states despite the presence of minimal structural disorder [4,5,6,7], cooperative paramagnetic states, in which the spins are locally correlated yet continue to fluctuate as T ~ 0 [8,9,10,11], and spin ice states [12,13,14,15,16,17,18,19,20,21], in which the spins freeze into a state analogous to that of the protons in frozen water. In this paper we report experimental results for variants of two spin ice materials, formed by increasing the density of spins present in the materials.…”