Field-induced antiferromagnetism and competition in the metamagnetic state of terbium gallium garnet

Abstract

The magnetic properties of the hyperkagome system of Tb 3 Ga 5 O 12 have been investigated by neutron scattering. Evidence of antiferromagnetic long-range order of the Tb moments at T N Յ 0.35 K in zero field is provided. With the application of magnetic field in the paramagnetic phase, ferromagnetic peaks initially appear at nuclear Bragg reflections. With the field higher than 3 Tesla, antiferromagnetic Bragg peaks appear as well indicating that the low-temperature magnetic phase extends well beyond the phase boundary, into the paramagnetic phase, with field. The new magnetic symmetry sets in at the metamagnetic transition in this system.When physical systems have access to more than one ground state, collective effects invoked from the competition or frustration of the interactions may emerge leading to exotic phases. 1 Even in crystals with pristine order, the presence of residual entropy at low temperatures is evidence of frustration inherent to the lattice. 2 In a typical crystal, atoms along with their magnetic moments, if present, are expected to follow certain symmetry rules. In magnetism, the Curie-Weiss, CW , temperature 3 defines an approximate scale at which point long-range ordering should appear. However, magnetic spinels, pyrochlores, and garnets defy this classic notion precisely because of their crystal symmetry. [4][5][6] If spins reside at the corners of triangular or tetrahedral lattices, the pairwise spin interactions cannot be simultaneously satisfied if they are to be aligned antiferromagnetically. 7 Such geometric frustration gives rise to a macroscopic degenerate ground-state manifold. In quantum spin systems, exotic collective effects may give rise to a resonating valence bond state. 8 In classical spin systems, frustration may lead to a spin-liquid state where the spins fluctuate continuously down to absolute zero, 9 or to a spin-ice state as in the paradigmatic hexagonal ice. 10,11 In the rare-earth ͑RE͒ garnets with Ia3d symmetry, the classical RE spin resides at the corners of triangles organized in two interpenetrating sublattices forming a hyperkagome structure 1 as seen in Fig. 1͑a͒. In some garnets such as the Gd 3 Ga 5 O 12 with a Heisenberg spin, magnetic long-range order is suppressed all the way down to ϳ0 K. 12,13 However, in garnets of the Tb family such as Tb 3 Al 5 O 12 , the paramagnetic ͑PM͒ state makes way to static antiferromagnetic ͑AF͒ order. 14 Intriguing is the Ising-like nature of the Tb spin with local axes that point in three orthogonal directions in the triangle, 15 producing a multiaxis magnet with potentially different responses to external perturbations such as an applied magnetic field. 14 The low-energy physics is dominated by two crystal-field ground-state singlets of this non-Kramers ion, while magnetic interactions which mixes them give rise to Néel order in the absence of an external magnetic field. 16,17 Thus, long-range dipolar interactions and nearestneighbor exchange interactions play an important role in determining the magnetic properties, and ...

Terahertz modulation of the Faraday rotation by laser pulses via the optical Kerr effect

“…A linear fit of the inverse frequency as a function of temperature (inset in Fig. 3 (d)) yielded the Curie-Weiss parameter Θ CW = −8.2 K, which matches well with that reported earlier 27 . All these observations support a linear relation between the oscillation frequency and the net magnetization of the medium.…”

Electrically active magnetic excitations in antiferromagnets (Review Article)

“…Magnetic-strictions properties of such garnet were considered in [87]. Investigation the dynamical properties of these interesting systems is just in the beginning [88][89][90]. Recent advance in THz time-domain spectroscopy may stimulate the investigations on a variety of kagome spin structure magnets to uncover the electric-dipole active magnetic resonances in these compounds.…”

Extension of the molecular-field theory on the magnetic behaviors in paramagnetic Dy3Ga5O12

“…Owing to the wide applications in optical, electronic, and magnetic materials and devices, the magnetic properties of rare-earth gallium garnets, especially the heavy rare-earth gallium garnets, have been intensively discussed during the past several decades [1][2][3][4]. Many experiments, mainly focused on the studies of susceptibility, magnetic moment, magnetic ordering and specific heat etc., in these garnets have been carried out, and some experimental phenomena are theoretically revealed by the analyses of the crystal field effect [5][6][7][8].…”