Using standard solid

state reaction method, multiferroic composite of 0.2 LNMFO + 0.8

BFO with LNMFO as ferrimagnetic and BFO as ferroelectric phase were prepared.

To prepare BFO stoichiometric amounts of high purity Bi2O3,

and Fe2O3 were weighed and mixed thoroughly in acetone

media for 5–6 h. The mixed powder of BFO was calcined at 800 °C in a closed

alumina crucible for 4 h and then pre-sintered at 850°C for 4 h. High purity Li2CO3,

NiO, MnCO3 and Fe2O3 were mixed in

stoichiometric amounts to prepare LNMFO by the same procedure as BFO. The well

mixed powder was calcined at 800 °C and pre-sintered at 1200 °C for 4 h. After

pre-sintering, powders were again grinded in an agate mortar. The obtained

powders of BFO and LNMFO were mixed in weight proportions in acetone media for

3–4 h to prepare 0.2BFO + 0.8LNMFO composite. From the composite powders pellet-

and toroid-shaped samples were prepared by applying a uniaxially pressure of

55MPa. Finally the samples were sintered at various sintering temperatures (Ts)

for 4 h and ready for characterizations.

2.2 Characterizations

X-ray diffraction (XRD) was carried out using a X-ray

diffractometer with CuK? radiation (?= 1.5418 Å). Surface morphology

were studied by Field Emission Scanning Electron Microscopy (FESEM, model JEOL

JSM 7600F). Energy Dispersive X-ray Spectroscopy (EDX) analysis was done by

using the EDX system supplied with the FESEM. The bulk density (?B)

of the composite was determined using the relation:

where m is the mass, r is the radius

and t is the thickness of the pellet. The X-ray density of the composite is

given by the formula,

where

is (1-x) times molecular weight of BFO and

is x times molecular weight of LNMFO,

(ferroelectric)

and

(ferrite) x is the weight fraction of LNMFO in the composites 22.

The ?x is measured by the general formula,

,

where n is the number of

atoms in a unit cell, M is the molar

mass of the sample, NA is

Avogadro’s number and V is the volume

of the unit cell. The porosity of the samples was calculated using the relation,

.

The dielectric and

magnetic properties were carried out using WAYNE KERR 6500B Impedance Analyzer.

To measure dielectric properties the samples were painted by conducting silver

paste on both sides. The dielectric constant (??) was calculated from the

capacitance using the formula:

, where C is the capacitance of the

pellet, A is the cross-sectional area of the electrode and

( = 8.85×10-12 F/m) is the

permittivity in free space. The relation:

,

where, ? is the angular frequency and tan?

is the dielectric loss, was used to calculate the ac conductivity (?ac).

The M-H hysteresis loop was observed using a vibration sample magnetometer

(VSM, model Micro Sense, EV9). The real part of the complex initial

permeability

was calculated using the relation:

,

where Ls is

the self-inductance of the sample core and

is derived geometrically. Here, L0 is the inductance of the

winding coil without the sample core, N is the number of turns of the coil (N =

4), S is the area of cross section and

is the mean diameter of the toroidal sample,

where d1 and d2 are the inner and outer diameter of the toroidal

sample, respectively 15. The output voltage

generated from the composite was measured using a Keithley multimeter (Model

2000) with of dc magnetic field. ME voltage coefficient (?ME) was calculated using relation 16

, where

is the ME voltage across the sample surface and h0 is the amplitude of the ac

magnetic field.

3.

Results and discussion

3.1

Crystal structure, density and porosity

Fig.

1 shows the XRD pattern of 0.2BFO + 0.8LNMFO composite. It is observed from the

XRD pattern that the composite confirms the presence of the ferrite and

ferroelectric phases. The lattice parameter of ferroelectric phase is measured

by solving different sets of three equations corresponding to three consecutive

peaks. Then by taking the average the accurate value of the lattice parameter

is obtained. The values of lattice parameter of all the peaks for the ferrite

phase obtained for each reflected plane are plotted against the Nelson–Riley

function 17:

, where ? is Bragg’s

angle. A straight line has been obtained and the accurate value of the lattice

parameter has been determined from the extrapolation of these lines to

.