Terahertz-frequency magnetoelectric effect in Ni-doped CaBaCo4O7

Abstract

We present a study of terahertz frequency magnetoelectric effect in ferrimagnetic pyroelectric CaBaCo 4 O 7 and its Ni-doped variants. The terahertz absorption spectrum of these materials consists of spin excitations and low-frequency infrared-active phonons. We studied the magnetic-fieldinduced changes in the terahertz refractive index and absorption in magnetic fields up to 17 T.We find that the magnetic field modulates the strength of infrared-active optical phonons near 1.2 and 1.6 THz. We use the Lorentz model of the dielectric function to analyze the measured magnetic-field dependence of the refractive index and absorption. We propose that most of the magnetoelectric effect is contributed by the optical phonons near 1.6 THz and higher-frequency resonances. Our experimental results can be used to construct and validate more detailed theoretical descriptions of magnetoelectricity in CaBaCo 4−x Ni x O 7 .

Enhancement of giant magnetoelectric effect in Ni-doped CaBaCo$_{4}$O$_{7}$

“…Temperature dependence of ME and dilatometric responses in zero field magnetic transitions are clearly observed at T N1 = 78 K and T N2 = 62 K in all the physical quantities. These observations are almost in accordance with the previous reports on the polycrystalline samples [33,34]. No hysteretic behavior can be seen at T N1 whereas a hysteresis is observed around T N2 in the M-T curves [Fig.…”

“…From the viewpoint of magnetism, the effect of partial chemical substitution on CBCO was systematically studied by many researchers [25][26][27][28][29][30][31][32][33][34]. One approach is the divalent Sr 2+ substitution for the nonmagnetic Ca 2+ /Ba 2+ , revealing that a few percent of Sr doping significantly suppresses the FIM ordering while maintaining the orthorhombic crystal structure [26][27][28].…”

“…This signals that the ferrimagnetism in undoped CBCO is quite sensitive to the local structural distortion. Another approach is the substitution for the magnetic Co, and it has been pointed out that the selective substitution of sites with the target valence is possible by a small amount of doping up to ∼20 % [29][30][31][32][33][34]. In the case of the nonmagnetic Al 3+ /Ga 3+ substitution for Co 3+ , the magnetic order is statistically destroyed at the benefit of magnetic frustration even though the Co2/Co3 ferromagnetic chains remain untouched.…”

“…Bearing in mind that giant ∆P is linked to the AFM-FIM transition in CBCO, one can expect that Zn 2+ or Ni 2+ doping, which brings AFM ground states as mentioned above, is a promising approach to control/enhance the ME effect. Such a study, however, has been so far limited to the polycrystalline samples of Ni-doped CBCO [33,34]. In this paper, we report a single-crystal investigation of the ME effect in CaBaCo 3.9 Ni 0.1 O 7 (CBCNO) by means of magnetization, electric polarization, dielectric constant, and magnetostriction measurements up to 50 T. In zero field, CBCNO undergoes successive magnetic transitions at T N1 = 78 K and T N2 = 62 K, both of which are found to accompany a negative change in ∆P along the c-axis.…”

Structural, magnetic and electric-polarization properties of geometrically frustrated YBaCo4O7and DyBaCo4O7cobaltites

“…In recent years a diverse interesting features, i.e. spin liquid phase [6] unidirectional THz absorption and magnetoelectric effects [7][8], and giant magnetic-field-induced polarization [9] were reported in RBaCo4O7 (R = Ca, Y and Rare earth) cobaltites. The crystal structure of these materials is built-up with alternating kagome and triangular layers, where the corners of the triangles occupied by magnetic cobalt ions and causes the frustration [10.11].…”