Successive Magnetic Transitions of Ca₂CoSi₂O₇in High Magnetic Fields

Abstract

Magnetic and dielectric properties of åkermanite Ca 2 CoSi 2 O 7 single crystals were investigated in pulsed high magnetic fields. In magnetic fields along the c axis, this material shows a magnetization plateau in a wide range of field below the saturation. Magnetization processes for fields along the a and b axes show multiple anomalies but different traces to each other, indicating the breaking of four-fold symmetry. Measurements of the magnetoelectric effects exhibit the changes in electric polarization according to the changes in the spin system. The experimentally determined quadratic magnetoelectric tensor is consistent with that expected in the crystal symmetry of orthorhombic P2 1 2 1

Direct observation of spin-quadrupolar excitations in Sr2CoGe2O7 by high-field electron spin resonance

“…Since inåkermanite materials electric polarization emerges even without applying poling electric fields, which is a unique feature of their multiferroicity [8,[11][12][13], we measured the polarization current without poling electric fields.…”

“…The * akaki@ahmf.sci.osaka-u.ac.jp lack of inversion symmetry at the tetrahedrally coordinated Co sites permits the magneto-electric effect, with on-site polarization proportional to the quadrupole operators already at a level of a single ion. The metal-ligand hybridization is believed to act in Ba 2 CoGe 2 O 7 [10,11], Sr 2 CoSi 2 O 7 [8], and Ca 2 CoSi 2 O 7 [12,13]. This mechanism is considered to be responsible for the dynamical properties of these materials, as it couples the spin degrees of freedom to the oscillating electric field component of the light.…”

Magnetic Structure and Dielectric State in the Multiferroic Ca2CoSi2O7

“…Small energy scale of the singleion anisotropy D is suggested by the magnetization measurements, 29,37,38) and proximity of the D and the exchange interaction would be the origin for the anomalous behavior in a high field. Detailed study on spin dynamics will be the key to the understanding of the relationship among the magnetization, the single-ion anisotropy, and the exchange interaction.…”

“…( electric properties 28,29) can be explained neither by the spincurrent model 8,12) nor the double exchange mechanism. 24,35) Accordingly, we consider the spin-dependent d-p hybridization mechanism 11) as in Ba 2 CoGe 2 O 7 .…”

“…While the magnetization in the low-H region was explained by the in-plane anisotropy, distinct anomaly for H [110] at 11 T and non-trivial magnetization plateau for H c-axis above 18 T 29) cannot be explained. Small energy scale of the singleion anisotropy D is suggested by the magnetization measurements, 29,37,38) and proximity of the D and the exchange interaction would be the origin for the anomalous behavior in a high field.…”