Single crystals of spinel Co 2 TiO 4 , CoTiO 3 of ilmenite structure and pseudobrookite CoTi 2 O 5 were grown by means of zone melting equipment URN-2-ZM. The growth processes were performed in an air atmosphere with a speed ~10 mm/h and a final annealing of the crystal at temperature of 1250 °C. Co 2 TiO 4 and CoTi 2 O 5 crystals were obtained with a diameter of 12-15 mm and length up to 60 mm, being free of any other phase inclusions and cracks. However, in the CoTiO 3 crystals some controversial features were found: x-ray Laue analysis indicated high-structure perfection while an electronic microscopy revealed small amount of second phase inclusions in contradiction to known phase diagram of this system. Electrical and magnetic properties of grown Co 2 TiO 4 and CoTiO 3 single crystals were studied. Semiconducting behavior of the Co 2 TiO 4 was established with the energy gap of ~1.3 eV. No magnetic anisotropy was found in the cubic Co 2 TiO 4 single crystals showing a magnetic behavior similar to polycrystals. The rhombohedral CoTiO 3 crystals revealed a magnetic behavior of an easy plane antiferromagnet with a significant anisotropy of the transverse magnetic susceptibilities along and perpendicular to the trigonal c axis.
Floating zone melting method with optical heating is elaborated to grow single crystals of the substituted hexaferrites BaTi x Co x Fe 12-2x O 19 and Sr x Ti x Co x Fe 12-2x O 19 (0.8 ≤ x ≤ 2). The dynamics of the growth process is studied and results of the analysis of impurity phases appearing in the initial stages of the crystal growth are presented. Compositions and unit-cell parameters of crystals are determined. Electrical, magnetic and magnetoelectric properties of grown crystals are investigated at temperatures 2-365 K and magnetic fields up to 50 kOe. It is shown that the resistivity of annealed in oxygen crystals at room temperature is ~ 10 6 Ohm•cm while at helium temperatures the crystals become good insulators. Magnetic measurements reveal conical spin structures in the crystals at some concentrations and temperatures. Magnetic field induced electric polarization of the low value (~ 0.3 µC/m 2 ) is detected at liquid helium temperatures for compositions with Ti and Co concentrations x = 0.8-0.9.
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