Single crystals growth of hexaferrits M-type MTixCoxFe12−2xO19 (M = Ba, Sr) by floating zone and investigation of their magnetic and magnetoelectric properties

Abstract

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.

Magnetostriction and magnetostructural domains in CoTiO$_3$

“…The region of significant lattice changes below 3 T applied in-plane coincides with the non-linear region in magnetization M vs. B measurements [18], signalling a spin-reorientation process in the ab-plane. This is particularly evident in Fig.…”

“…1). In particular for CoTiO 3 , early magnetization [17,18] and neutron diffraction experiments [19] indicated a long-ranged easy-plane type antiferromagnetic structure below T N = 38 K. Furthermore, recent inelastic neutron scattering experiments on CoTiO 3 exhibited the presence of Dirac magnons [20] and rendered it as a model system to study non-trivial magnon band topology [21,22]. Here, we present macroscopic magnetization and magnetostriction (dL(B)/L) measurements on CoTiO 3 .…”

Magnetic phase diagram, magnetoelastic coupling and Grüneisen scaling in CoTiO$_3$

“…II) implies the main ilmenite (R 3) phase as well as the secondary TiO 2 (Rutile) and the spinel (Co 2 TiO 4 ) phase in both air and oxygen atmosphere grown crystals. Such secondary phases were observed as inclusions in previously reported CoTiO 3 crystals by Balbashov et al [11] and ascribed to high-temperature gradients at the growth interface. A qualitative comparison of the relative intensities of impurity peaks from room temperature XRD data reveals that the spinel Co 2 TiO 4 phase is present in larger proportions in air-grown than in oxygen-grown single crystals (where it is hardly visible; see Fig.…”

“…In a particular ab plane, the magnetic Co 2+ ions are interconnected via the O 2− ions and exhibit a buckled honeycomblike structure [8]. The neutron-diffraction studies performed as early as 1964 by Newnham et al [9] and more recently by Elliot et al [10] on polycrystalline samples, reveal a long-ranged twosublattice, easy-plane type antiferromagnetic structure below T N = 38 K [11,12], with ferromagnetically aligned Co 2+ spins lying in the ab plane and the layers being coupled antiferromagnetically along the c axis. The easy-plane type magnetic anisotropy is due to a combined effect of crystal-field effects and spin-orbit coupling on high-spin 3d 7 Co 2+ ions effectively leading to a pseudospin-1/2 ground state [13][14][15].…”

Magnetic and dipole moments in indium doped barium hexaferrites

“…Mechanism for its realization is also important [11][12][13][14]. This question presents both fundamental scientific interest and it is important from a practical point of view [15][16][17][18][19][20][21][22][23][24][25]. Some controversy about ferroelectricity in the M-type hexaferrites exists [26].…”