Uniaxial magnetic anisotropy in Co2.25Fe0.75O

J. Bartolomé

¹

,

Ana B. Arauzo

²

,

N. V. Kazak

³

et al.

Abstract

Magnetic and Mössbauer spectroscopy (MS) measurements have been performed on a single crystal of Co 2.25 Fe 0.75 O 2 BO 3 with ludwigite structure. Two magnetic transitions (T N = 115 K and T C = 70 K) were traced from the ac susceptibility temperature dependence. The MS spectra as a function of temperature clearly show the onset of magnetic ordering below 115 K. Magnetization measurements on the parent Co 3 O 2 BO 3 and Fe 3 O 2 BO 3 compounds have been done for comparison. In Fe 3 O 2 BO 3 the anisotropy of the different phases has been determined, showing that the anisotropy axis changes from the a to the b axis in the low-temperature antiferromagnetic phase. High magnetic uniaxial anisotropy has been detected for both Co 3 O 2 BO 3 and Co 2.25 Fe 0.75 O 2 BO 3 . From the angle-dependent magnetization measurements it is found that in both compounds the easy axis of magnetization is the b [010] axis, where an antiferromagnetic component is superimposed on the main ferromagnetic component. In the c direction the behavior is purely antiferromagnetic. In Co 2.25 Fe 0.75 O 2 BO 3 a strong reduction of the remanent magnetization and a very strong increase in coercive field along the b axis with respect to those found in Co 3 O 2 BO 3 were observed from magnetic hysteresis cycles measured below T C . The increase of coercive field is caused by the increase of defects upon Co substitution by Fe.

Structure and magnetism of copper-substituted cobalt ludwigite Co3O2BO3

“…The high field branches of the loops are close to linear pointing out the possible antiferromagnetic contribution to the magnetic moment. The observed M(H) behavior is very similar to the parent Co 3 O 2 BO 3 [9]. It seems that in both compounds the magnetic ordering at 43 K is of ferrimagnetic character.…”

“…The Co-ludwigite samples are highly anisotropic [9], so the magnetic measurements have be done in magnetic field directed along different crystallographic axes. In our experiment the sample was oriented by the x-ray diffractometer and then attached to the plexiglas cube by glue.…”

“…These oxyborates may crystallize into a large variety of crystallographic structures named after the natural minerals: calcite, hantite, pyroborate, cotoite, warwickite and ludwigite [1][2][3][4][5]. The latter compounds known as ludwigites at last few years forced the high wave of interest due to their extremely unusual magnetic properties [6][7][8][9][10]. For example, one from two known homometallic ludwigites Fe 3 O 2 BO 3 seems to possess at least two magnetic sublattices, which order orthogonally at temperatures 110 and 70 K [7,9].…”

“…The latter compounds known as ludwigites at last few years forced the high wave of interest due to their extremely unusual magnetic properties [6][7][8][9][10]. For example, one from two known homometallic ludwigites Fe 3 O 2 BO 3 seems to possess at least two magnetic sublattices, which order orthogonally at temperatures 110 and 70 K [7,9]. In our previous works we have concentrated on the properties of the second homometallic ludwigite Co 3 O 2 BO 3 and intermediate compounds Co 3-x Fe x O 2 BO 3 (x ≤ 1) [5,9,10].…”

“…For example, one from two known homometallic ludwigites Fe 3 O 2 BO 3 seems to possess at least two magnetic sublattices, which order orthogonally at temperatures 110 and 70 K [7,9]. In our previous works we have concentrated on the properties of the second homometallic ludwigite Co 3 O 2 BO 3 and intermediate compounds Co 3-x Fe x O 2 BO 3 (x ≤ 1) [5,9,10]. The high quality and large enough crystals of these materials became available not long ago [5,6].…”