Static Critical Behavior of the Spin-Freezing Transition in the Geometrically Frustrated Pyrochlore AntiferromagnetY2Mo2

Abstract

Some frustrated pyrochlore antiferromagnets, such as Y2Mo2O7, show a spin-freezing transition and magnetic irreversibilities below a temperature T f similar to what is observed in randomly frustrated spin glasses. We present results of DC nonlinear magnetization measurements on Y2Mo2O7 that provide strong evidence that there is an underlying thermodynamic phase transition at T f , which is characterized by critical exponents γ ≈ 2.8 and β ≈ 0.8. These values are typical of those found in random spin glasses, despite the fact that the level of random disorder in Y2Mo2O7 is immeasurably small. The past five years have seen a resurgence of significant interest devoted to the systematic study of geometrically frustrated antiferromagnets [1][2][3][4]. Geometric frustration arises in materials containing antiferromagneticallycoupled magnetic moments which reside on geometrical units, such as triangles and tetrahedra, that inhibit the formation of a collinear magnetically-ordered state. The main motivation for the current interest in these systems stems from suggestions that (i) they may display critical phenomena belonging to a "new" chiral universality class different from the universality classes of collinear magnets [2,4], or (ii) the increased propensity of frustrated antiferromagnets for quantum zero-temperature spin fluctuations compared to collinear antiferromagnets might be sufficient to destroy Néel order and drive these systems into novel non-classical quantum disordered ground states [2,3].Systems of classical Heisenberg spins residing on lattices of corner-sharing triangles or tetrahedra and antiferromagnetically coupled via nearest-neighbor exchange constitute particularly interesting cases of highly frustrated antiferromagnets (see Fig. 1). Here, theory [5,6] and numerical work [7], show that these systems do not order and remain in a "collective paramagnetic state" [5] down to zero temperature. Since, even for classical spins, these systems have such a small tendency to order, they are excellent candidates to display exotic quantum disordered ground states [2,3,8]. However, and perhaps most interestingly, experiments show that some nominally perfect (i.e. disorder-free) [9] pyrochlore antiferromagnets [10] exhibit a spin-freezing transition at some temperature T f , below which they develop magnetic irreversibilities (see Fig. 1) and long-time magnetic relaxation similar to what is found in conventional randomly frustrated spin glasses such as CuMn, EuSrS, and CdMnTe [11].

Structural properties of the geometrically frustrated pyrochloreTb2Ti2OHan1, Gardner2, Booth3 2004Phys. Rev. B513320View full textAdd to dashboardCite

“…Analysis of the Debye temperatures and the correlations between various site displacements show that, vibrationally, the Tb and Ti sublattices are partially decoupled, and that the more plentiful O(1) atoms are more tightly bound to the Ti sites. This compound, with its near absence of local and bulk structural disorder and antiferromagnetic nearest-neighbor interactions, 15,38 is therefore an appropriate system to study the elusive 3-dimensional, low-temperature, spin liquid.…”

Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution

“…The different behavior between the ZFC and FC processes excludes the existence of a spin liquid state and suggests the occurrence of a spin-glass-like state. 37,38 The appearance of spin-glass-like state could be due to the competition interaction among Mn-O-Mn, Fe-O-Fe, Mn-O-Fe, and even Tb-Mn or Tb-Fe. 39 Unfortunately, current work cannot define the exact competition interaction.…”

Short-range order in the topological spin glass(D3O)Fe3(Wills1, Oakley2, Visser3 et al. 2001Phys. Rev. B407270View full textAdd to dashboardCite

“…In fact, the variety of exotic low-temperature physics exhibited in these lattices is astounding, e.g., topological spin glass, spin fluid, spin ice, colossal magnetoresistance, heavy fermion, and superconductivity. One particular area of interest involves the possibility of disorder-free spin-glass states, of the types observed in the kagomé antiferromagnet (H 3 O)Fe 3 (SO 4 ) 2 (OH) 6 [2][3][4][5][6][7][8][9][10][11][12] These spin-glass states are believed to be a consequence of the vertex sharing geometries, and they have been termed topological spin glasses in order to distinguish them from conventional sitedisordered systems. 13,14 In this article we report xyz polarized neutron-scattering measurements of a powder sample of the two-dimensional ͑2D͒ kagomé antiferromagnet (D 3 O)Fe 3 (SO 4 ) 2 (OD) 6 between 1.5 and 250 K. Unpolarized neutron-diffraction measurements of this material are hindered by the large background from strong nuclear Bragg reflections and incoherent scattering from protons present in partially deuterated samples.…”