Using LNMFO were mixed in weight proportions in

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

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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

.