Transition metal (Ni,Mn) codoped Zn3P2 nanoparticles: effect on structural, optical and magnetic properties

This work reports the pure matrix and synthesis of Zn(3–(x+y))NixMnyP2 (x = 0.02, y = 0.01, 0.03, 0.05, and 0.07) nanoparticles using the solid-state reaction method. The impact of Ni-Mn codoping on the structural, morphological, chemical identification, optical, photoluminescence, and magnetic properties of Zn3P2 nanoparticles is studied. The structural properties after doping confirm the absence of other phases and synthesized samples had a tetragonal structure. Using SEM with EDAX, the nanoparticles’ surface morphology, and elemental composition are investigated. The nanoparticles have a spherical shape and approximately the expected stoichiometric atomic ratio. The optical band gap of the undoped and codoped nanoparticles is calculated and found the band gap increased with increasing dopant content. The emission peaks show that all emission peaks are in the same wavelength position with effect of dopant level. VSM confirmed the magnetic moment is found to increase with an increase in dopant concentration.


Introduction
Investigation of dilute magnetic semiconductors (DMSs) is strongly motivated by the growing Spintronic paradigm of a spin-based multifunctional device.Spintronics has few benefits on conventional charge-based devices regarding data processing quickly, better integration densities, etc.The diluted magnetic semiconductors combine both properties of magnetism and semiconducting, therefore, DMSs are considered a particular material for spintronics where spin and charge of the electron are used to perform several functions.DMSs are produced when a portion of the cation of undoped host lattice is replaced by magnetic ions such as transition elements (Cr, Mn, V, Fe, Co, Ni) and rare earth elements in II-VI, IV-VI, and III-V group semiconductor compounds.As spin-based multifunctional devices provide nonvolatility, better integration densities, reduced power consumption, and faster data processing, spintronics applications are currently an active field [1].For the future generation of nanoelectronics devices, spintronics is one of the burgeoning topics.In these devices, the spin polarisation is adjusted either by magnetic layers used analysers or spin-orbit coupling, or spin polarizers.Moreover, spin current can be carried via spin waves [2].Realizing and manufacturing spintronics-based devices is the main challenge.The scientific community is creating novel materials that rely on magnetism rather than the flow of electricity through electrons to achieve the desired results [3].In the past decades, several researchers investigated ferromagnetism in diluted magnetic semiconductors at room temperature and higher temperatures.
The creation of new spintronic material that makes use of both electron charge and spin for application is the subject of extensive research.In this regard, the class of II-VI group diluted magnetic semiconductor materials (DMS) such as magnetic ions substituted Cr-doped ZnTe [4], Mn-doped ZnSe [5], Co-doped CdTe [6], and Cudoped CdSe [7] were studied and reported structural, optical and magnetic properties.These DMS materials mostly reported ferromagnetism at room temperature.
The class III-V group DMS materials are Cr-doped GaSb [8], Cr-dope AlP [9], and Mn-doped InP [10].Based on our literature review, the transition elements doped in host lattice exhibited magnetic behavior.Researchers investigated less work on these compounds compared to II-VI group compounds.
In the class IV-VI group DMS materials, most of the work done on oxides are of Fe-doped SnO 2 [11], and Co-doped TiO 2 [12].Moreover, several researchers worked on thin films.DMS materials, increasing the Curie temperature (Tc) above room temperature is one of the key factors.The other is the fundamental problem of ferromagnetism's nature and origin in low-carrier density semiconductor devices that were studied in the literature review of Co-doped TiO 2 films [12].Most of the researchers investigate the physical properties of II-VI, IV-VI, and III-V DMS compounds doped with transition elements or rare earth elements.Especially these compound materials offer unique device applications such as data processing and storage systems.
The present work investigated the properties of transition elements (Ni, Mn) codoped Zn 3 P 2 nanoparticles and found their different characteristics.The agenda of this research, Zn is a (II) group transition metal, and P is a V group reactive non-metal.P and Zn are both diamagnetic materials and codoped transition metals (Ni, Mn) in Zn 3 P 2 .Based on this compound (Zn 3 P 2 ) in the past decades, less work has been done compared to other DMS compound materials.From the literature survey, we can see the Zn 3 P 2 is very similar to that of cadmium phosphide (Cd 3 P 2 ), zinc arsenide (Zn 3 As 2 ), and cadmium arsenide (Cd 3 As 2 ).Utilizing ab initio studies based on density functional theory (DFT), researchers looked into structural, magnetism and electrical properties.G. Jaiganesh et al [13] examined the establishment of magnetic order in one and two Ti atom substituted Cd 3 P 2 as well as metallic properties in this system.Mn-doped Zn 3 As 2 using the modified Bridgman method (a melt in a furnace slowly cooling in the presence of a temperature gradient) discussed magnetic properties with lower dopant concentration from 0.08 to 0.13 and it varies with temperature [14].Mn-doped Cd 3 As 2 , using a temperature range of 0.5 K< T < 300 K and a magnetic field range of up to 25 T for x <18%, this research discusses the parameters of their specific heat, susceptibility, and magnetization [15].Ti-doped Zn 3 P 2 , utilizing the density functional theory-based ab-initio computations, discussed the ferromagnetic phase and single Ti atom substituted in the undoped lattice since the total energy associated with the ferromagnetic phase is smaller than the nonmagnetic phase.Zn 3 P 2 is more stable after doping the Ti atom and investigates the electronic and magnetic properties [16].Fe-doped Zn 3 P 2 using first principle calculations based on density functional theory discussed the effect of low Fe dopant concentration on the ferromagnetic stability, half-metallic ground state and total energy in the ferromagnetic phase (FM) and nonmagnetic phases (NM).The large magnetic moment was observed due to the Fe-doping on an undoped lattice and investigated electronic and magnetic structure [17].Transition elements (TM=V, Cr, Mn, Fe, Co) doped Zn 3 P 2 discussed the effect of dopant concentration on the structural stability, half-metallic property, and magnetic and spin-dependent density of states [18].
Zn 3 P 2 is an earth-abundant, mixed-valent, polar, and P-type compound semiconductor.It is an inexpensive DMS material that is easy to produce into a thin film and has excellent potential as a photovoltaic material.At ambient circumstances, the crystal structure of Zn 3 P 2 is a simple tetragonal structure with the P42/nmc space group (No.137) [19].Stackelberg and his team discussed the structure of undoped lattice (Zn 3 P 2 ) [20].The band gap for single-junction solar cells [21].As per the numerous reports of solar cells based on Zn 3 P 2 , it is a great material for solar cells [22,23].It may also be suitable for other optoelectronic devices including infrared (IR) [24], ultraviolet (UV) sensors [25,26], and lithium-ion batteries [27].Lengthy minority carrier diffusion length (5-10 μm) [28].Optical characteristics of Zn 3 P 2 thin films are appropriate for use in photovoltaic cells [29].The review of Zn 3 P 2 compounds only focused on a single transition element doped and found their structural, electrical and magnetic properties based on ab initio studies with density functional theory.There are no reports on the synthesis of Zn 3 P 2 by codoping with two transition elements.The present work focused on the synthesis and investigation of structural, optical, and magnetic properties of Zn 3 P 2 nanoparticles codoped with two transition elements (Ni, Mn) at various dopant concentrations.Moreover, photoluminescence, surface morphology, and chemical identification.According to a survey of Zn 3 P 2 DMS, this material could be useful for semiconductor spintronic devices.

Experimental work 2.1. Synthesis of Ni-Mn codoped Zn 3 P 2 nanoparticles
The experimental work aims to prepare Ni-Mn codoped Zn 3 P 2 nanoparticles by using the solid-state reaction method.Zn 3 P 2 (Sigma Aldrich), Ni 2 P (Sigma Aldrich), and Mn 3 P 2 (Thermo scientific) powders were used as starting materials for synthesis.These three chemicals were weighed by the stoichiometric ratio of Zn (3-(x +y)) Ni x Mn y P 2 where x = 0.02 and y = 0.01, 0.03, 0.05, and 0.07 for the synthesis of Ni-Mn codoped Zn 3 P 2 nanoparticles.The as prepared four different samples are named as: Z-1:Zn 0.97 Ni 0.02 Mn 0.01 P, Z-2: Zn 0.95 Ni 0.02 Mn 0.03 P, Z-3:Zn 0.93 Ni 0.02 Mn 0.05 P, and Z-4: Zn 0.91 Ni 0.02 Mn 0.07 P respectively.According to the solid-state reaction process, first, clean agate mortar and pestle with the help of acetone.Then weigh the powders and they are thoroughly grounded in an agate mortar and pestle to create extremely fine powders.For each Ni-Mn doped powder sample, the mixture was grinded for a total time of 16 h.For the synthesis of the current samples, the grinded powder samples were transferred to an alumina crucible with a fixed plate and evacuated at 2 × 10 −2 mbar using a rotary pump.All Ni-Mn codoped samples were maintained for 5 h at 500 °C in a horizontal tubular microprocessor-controlled furnace.After sintering, the samples were again thoroughly grinded for 3 h before characterizations.Before and after sintering, we observed the color of powder samples changed and it appeared in pure dark color.

Characterizations techniques
Prepared Ni-Mn codoped zinc phosphide nanoparticles were subjected to several characterization techniques to study their structural and phase (XRD), morphological (SEM), elemental (EDAX), optical (UV-vis-NIR), photoluminescence (PL), and magnetic properties (VSM).The structural characteristics of the nanoparticles were investigated using a powder X-ray diffraction (Rigaku-mini flex-600) with Cu Kα radiation λ = 1.5406A°.The surface morphology studies were recorded in the range of 500 nm and elemental analysis was carried out using energy-dispersive x-ray analysis (JSM-IT 500).The reflectance and optical band gap were carried out by the UV-vis-NIR spectrometer (Perkin lambda 365).Emission spectra was found by photoluminescence spectrometer (Fluorescence spectrum FP-8300).Magnetic moment measurements were measured by a Vibrating sample magnetometer (Lakeshore 7410 S).All of the synthesized diffraction peaks were found in the XRD pattern and are very strong and sharp, suggesting the high crystalline form of Ni-Mn codoped Zn 3 P 2 nanoparticles.No additional secondary diffraction peaks of Ni or Mn-related impurity phase were not found, proving that the dopant ions in the Zn 3 P 2 have been properly substituted.The diffraction peaks of the synthesized sample were all found to coincide with the tetragonal structure of Zn 3 P 2 .I.K.El Zawawi discussed the tetragonal structure of Zn 3 P 2 [30].

Results and discussion
The undoped and Ni-Mn codoped Zn 3 P 2 nanoparticles are shown in figure 2 at an angle of 2θ between 43.5°a nd 46.0°.In the analysis of XRD data, the primary diffraction peak is identified as (4 0 0) and its corresponding angle is 44.8°.As the dopant concentration rise from Z-1 to Z-4 samples, the diffraction peaks are shifted to the side of higher angles.It might be caused by the ionic difference between pure Zn +2 (0.74 Å), dopant Mn +2 (0.66 Å), and dopant Ni +2 (0.69 Å).
The ionic difference between the two dopant ions is small compared to the undoped lattice.This is because the Ni and Mn atoms have settled in the Zn sites, slightly shifting the diffraction peaks to the higher angle side range from 44.3°to 45.5°.In the Z-4 sample diffraction peak shifting is highest compared to other samples.It indicates magnetic ions are more in undoped lattice and as a result shifting increases.For comparison (II-V) group compounds, there were no proper reports on Ni-Mn codoped Zn 3 P 2 using different dopant transition elements.
Scherrer's formula was used to determine the average crystallite size (D) for undoped and Ni-Mn codoped samples, and the resulting equation is displayed below [31] Where K is the Scherrer constant, and its value is 0.9, λ stands for the wavelength of Cu-Kα radiation (1.541 Å), β represents the full width at half maximum (FWHM, in radian), and θ represents the diffraction angle (in radian).The crystallite size of the undoped lattice (4 0 0) plane is 25.11 nm.After doping, crystallite size for Z-1 sample is 27.27 nm, Z-2 is 26.06 nm, Z-3 is 32.27 nm and the final Z-4 is 31.26nm as mentioned in table 1.The average crystallite size of Zn 3 P 2 calculated was noticed to be 16.86 nm.Following are the average crystallite size of codoped samples as Z-1 is 18.06 nm, Z-2 is 19.06 nm, Z-3 is 23.23 nm, and Z-4: is 23.88 nm.
Figure 3 shows the plot of crystallite size and microstrain with different dopant concentrations.The microstrain (ε) was calculated using the following equation [32]: Table 1.Table of angle   Where the symbol β represents full width at half maximum (FWHM, in radians) and θ defines an angle of diffraction patterns (also, in radians).Microstrain for the undoped lattice is 1.388 and the dopant concentration of Z-1 is 1.271, Z-2 is 1.33, Z-3 is 1.074, and the final concentration of Z-4 is 1.109.The dislocation density (δ), which is defined as being inversely proportional to the square of the average crystallite size, is used to quantify the small number of defects present in the crystal structure of Zn 3 P 2 , and it is represented as follows [32]: Where D is crystallite size in nanometres, the undoped lattice dislocation is 1.585 after the effect of Ni-Mn dopant concentration Z-1 is 1.344, Z-2 is 1.472, Z-3 is 0.960 and final dopant concentration of Z-4 is 1.022.It was observed that in table 1 the dislocation density and microstrain decrease with an increase in crystallite size, which indicates a lower number of lattice imperfections.
From the XRD results based on JCPDS card data, the lattice parameters of the undoped lattice and Ni-Mn doped samples were observed.The standard structure of Zn 3 P 2 is a tetragonal crystal structure and this structure identifies lattice points a = b = 8.0970 Å and c = 11.4500Å and angels α = β = γ = 90°(in JCPDS).According to the experiment, the host lattice parameters show a = b = 8.1338 Å and c = 11.4596Å, and similarly, all codoped samples' lattice parameters were calculated by using the tetragonal structure formula.
The effect of dopant concentration in host lattice, the lattice parameters are slightly decreased from Z-1 is a = b = 8.1269 Å, c = 11.4448Å to Z-4 is a = b = 8.0211 Å, c = 11.4048Å.This is mainly due to the smaller ionic radius of two dopants (Ni-Mn) ions and depending on Zn sites.Based on these results it can be confirmed the less ionic radius of dopants, they easily settled in the host lattice compound and confirmed Ni-Mn was properly doped in the undoped lattice.Using the Zn 3 P 2 tetragonal structural relation, estimated lattice parameters were represented as: Bragg's equation (n l = 2dsinθ), where d is the interplanar spacing, n is the order of diffraction equal to one, θ defines the angle of Bragg diffraction, λ (1.5406 Å) is the wavelength of the incident beam, h, k, and l is miller indices of x-ray diffraction planes.X-ray diffraction parameters such as crystallite size, lattice parameters, dislocation density, microstrain, and optical band gap are mentioned in table 1.

Morphological studies
A focused stream of electrons is used to scan the surface of a material using an electron microscope known as a scanning electron microscope (SEM) to create images.As a result of the electrons' interactions with the sample's atoms, a variety of signals that provide details on the surface topography are generated.Figure 4 shows the Ni-Mn codoped Zn 3 P 2 nanoparticles in the range of 500 nm.According to XRD results, the crystallite size is mentioned in table 1.The crystallite size is very less compared to SEM images.This may be due to the effect of dopant concentration and temperature.The Z-1 sample shows particle sizes 125 nm and 275 nm and spherical shapes were observed.Similarly, the concentration of Z-2 sample particles is visible but slightly agglomeration increased.For the Z-3 sample particle size and agglomeration increased compared to the Z-2 sample and finally the concentration of Z-4 sample all the particles closed together.

Elemental composition
The composition of a sample, including powders, thin films, and other kinds of materials, can be ascertained using Energy dispersive x-ray analysis (EDAX).Additionally, it is possible to trace the distribution of the atoms in our samples, measuring the relative amounts of each atom.The elemental composition identifies the present prepared samples namely Z-1, Z-2, Z-3, and Z-4 samples, as illustrated in figure 5.The elements Zn, P, Ni, and Mn were present in the EDAX spectra.All codoped concentrations nearly matched the expected atomic ratio and there are no other impurities involved.From this we can conclude that Ni-Mn was properly substituted in the undoped lattice and confirmed the purity of Ni-Mn doped Zn 3 P 2 nanoparticles.The X-ray diffraction results with proof of EDAX spectra confirmed that dopants are inserted in the undoped lattice.

Optical properties
Figure 6 shows the diffused reflectance spectra (DRS) of pure lattice and Ni-Mn codoped ZnP 2 nanoparticles recorded at room temperature at various dopant concentrations such as Z-1, Z-2, Z-3, and Z-4 samples.The reflectance spectra were studied using a UV-vis-NIR spectrometer.To determine the energy band gap of the  Ni-Mn codoped Zn 3 P 2 nanoparticles, absorption spectra were also obtained in addition to reflectance spectra (absorption plot not provided here).
The reflectance plot was recorded in the wavelength of 400 nm to 1200 nm.In the reflectance spectra, the undoped lattice exhibited the highest reflectance observed in the IR region 800 nm to 1100 nm.All synthesized samples show less reflectance in the IR region.Pure and codoped samples with less reflectance were observed in the visible region.The reflectance changes due to the effect of dopant concentration from Z-1 to Z-4 samples.
Figure 7 shows the optical band gap of undoped lattice and synthesized samples.A Kubelka-Munk function relation was used to calculate the absorption coefficient.
Where α is a function of reflectance related to the absorption coefficient (F(R) = α) and R is the reflectance of the given undoped and codoped samples.The energy gap is the term used to describe the intrinsic bandgap absorption brought on by an electron moving from the valence band to the conduction band.The optical bandgap was calculated for the undoped lattice and codoped samples by using Tauc's plots equation.
where F(R) = α is the absorption coefficient, R is the diffused reflectance of the samples, A is a constant independent of wavelength, hν is the energy of the photon (h is a plank constant and ν is a frequency), and the  The direct energy band gap of the pure lattice Zn 3 P 2 is 1.5 eV in agreement with M Bhushan [21].In the undoped lattice and synthesized samples, the optical band gap increased with increasing dopant concentration.The band gap of the undoped lattice is 1.410 eV, Z-1 sample is 1.414 eV, Z-2 sample is 1.422 eV, Z-3 sample is 1.432 eV, and a final concentration of Z-4 samples is 1.445 eV.Burstein-Moss effect could be the cause of the increased optical band gap observed with increasing Ni-Mn concentration.The band gap widens as a result of the Fermi level moving to the conduction band and occupying some of its bottom levels, making the transition from the valance band to the conduction band more energy-intensive.There is no proper reference to the codoping effect of undoped lattice using magnetic impurity and experimental analysis.Previously, most of the research was done on first-principles calculations based on the density functional theory.

Photoluminescence studies
Photoluminescence analysis is a potent characterization for determining the various structural flaws and optical quality of nanoparticles through the identification of different trapping and recombination levels of photogenerated carriers.Notably, structural faults such as zinc and phosphor interstitials lead to various radiative recombination transitions between electrons belonging to either the conduction band or trapping levels and holes belonging to either the valence band or trapping levels when present in Zn 3 P 2 nanosized structures.The analysis of the effects of doping Zn 3 P 2 nanoparticles with Ni 2+ and Mn 2+ ions on their PL spectra at excitation wavelengths of 244 nm and 195 nm is the focus of the current work.
Figure 8 (a) shows pure and Ni-Mn doped Zn 3 P 2 nanoparticles with an excitation wavelength of 244 nm in the wavelength region from 200 nm to 600 nm.Based on the excitation wavelength were observed four emission bands such as 297 nm (4.17 eV) is an ultraviolet region, 393 nm (3.15 eV) is a violet color and the remaining two emissions were 467 nm (2.65 eV), 486 nm (2.54 eV) is a green region.Undoped lattice exhibited the highest intensity and codoped samples exhibited less intensity in the wavelength range of 275 nm to 500 nm.PL intensity increase with an increased dopant concentration from Z-1 to Z-4 samples.No peak shift was observed with an increased dopant concentration.Strong emissions at 393 nm and three weak emissions at 297 nm, 467 nm, and 486 nm were seen.
Figure 8 (b) shows the undoped lattice and Ni-Mn doped nanoparticle excitation at 195 nm in the wavelength range of 150 nm to 300 nm.From these spectra, we observed one emission peak at 243 nm (5.10 eV) in the ultraviolet region.The undoped lattice exhibited maximum intensity compared to codoped samples in the ultraviolet region.The PL intensity increases with increasing dopant concentration from Z-1 to Z-4 samples and no emission peak shifts were observed even at higher dopant level.
The direct band of the pure matrix is 1.5 eV [21].Presently the obtained direct band gap of the undoped lattice is 1.410 eV and the codoped sample's band gap range from 1.414 eV to 1.445 eV as shown in figure 8. Based on the emission peaks the band edge does not correlate to the optical band gap of undoped and codoped samples.This may be due to shallow and deep traps below the conduction band produced as a result of surface imperfections in nanoparticles [33].To the best of our knowledge, no reports were found on the photoluminescence activity of transition metal (Ni-Mn) codoped Zn 3 P 2 nanoparticles.According to [34], a previous study of Cu-doped ZnO nanocrystals discussed the deconvolution of the undoped ZnO emission spectra exhibits bands with centers at 356, 397, 430, and 515 nm.Supporting the mechanism of radiative transition proposed for the undoped ZnO nanocrystals, it was determined that the band-to-band radiative transition was responsible for the weak UV emission band at 356 nm (3.49eV) at an excitation wavelength of 325 nm and emission centers at 534 nm, 598 nm, and 638 nm with excited at 383.A.A. Othman et al discussed [35] Mn-doped ZnO emission at 397 nm.

Magnetic properties
The vibrating sample magnetometer (VSM) is used to assess the magnetic properties of solids and liquids.Presently, we estimated the magnetic moment for pure and Ni-Mn codoped powder samples with an applied magnetic field.Figure 9 (a) shows the magnetic hysteresis (M-H) loops of the pure in the range of +15000 Oe, 9 (b) Ni-Mn doped nanoparticles in the range of +15000 Oe, and 9 (c) Ni-Mn codoped nanoparticles in the range of +400 Oe obtained by VSM at room temperature (300 K).
The M-H loop graphic shows that the undoped matrix and codoped sample exhibit ferromagnetic properties.Figure 9 (a) clearly shows the undoped matrix exhibited ferromagnetism behavior in the field range of + 15000 Oe.The undoped lattice is a combination of II-V group compounds, generally, both elements exhibit diamagnetic behavior theoretically but the plot of the M-H loop shows ferromagnetism.This may be due to the formation of the compound in nanoscale range of Zn 3 P 2 (II-V).The pure matrix is procured by Sigma Aldrich Company its purity is 19% active phosphor (P) basis powder.This plot confirms the ferromagnetic nature merged in the diamagnetic matrix of the pure matrix.In the literature on pure matrix, it is not possible to show the diamagnetic behavior but it shows stable ferromagnetic behavior at room temperature [36].The pure matrix observed three parameters saturation magnetization (Ms) is 0.0882 emu g −1 coercivity (Hc) is 89.806Oe, and retentivity (Mr) is 0.0066 emu g −1 .
Figure 9 (b) shows the M-H hysteresis loop of Ni-Mn codoped Zn 3 P 2 nanoparticles in the applied field range of +15000 Oe.By the effect of Z-1 dopant concentration, the saturation magnetization (Ms) became 0.0433 emu g −1 , coercivity (Hc) became 128.680Oe and retentivity (Mr) became 0.0031 emu g −1 .The strength of magnetization decreased with increase of dopant concentration (Z-1) compared with undoped lattice.This may be due to the undoped lattice replacement of some atom's positions with the effect of magnetic ions.According to [16], the magnetic ion doped Zn 3 P 2 is a more stable ferromagnetism phase using ab initio studies.Based on the literature review [17] discussed, doped cation (Fe) d-like electrons are primarily responsible for the magnetic order.The substantially spin-split doped cation d-like state is located close to the Fermi level.G. Jaiganesh et al [18] discussed the transition elements doped into Zn 3 P 2 lattice, discovered to produce the magnetic order and a half-metallic characteristic is noted.The M-H loops indicate the saturation magnetization values of Z-2, Z-3, and Z-4 samples are 0.0521 emu g −1 , 0.0896 emu g −1 , and 0.2517 emu g −1 .From these results, it is confirmed that saturation magnetization is increased by higher exchange contacts between Zn 3 P 2 and Ni-Mn concentrations.From the x-ray diffraction results of codoped Zn 3 P 2 nanoparticles, it is confirmed that there are no other impurities or the presence of Ni-Mn elements, and the possibility of ferromagnetism increased because the two dopant ions properly inserted in the undoped lattice.The saturation magnetization of the Z-4 sample is higher than that of the Z-1 sample, and the values of saturation magnetization increase with an increase in Ni-Mn concentration.The doped cation's (Ni-Mn) d-like electrons are primarily responsible for the ferromagnetism.The doped cation d-like state is significantly spin-split and located near to the Fermi level.According to [18], the density of states of the Cr atom exhibits considerable exchange splitting, which results in a significant magnetic moment.Cr induces a half-metallic property where the spin-down density of states of Cr exhibits a gap while the spin-up density of states exhibits a finite value at the Fermi energy.After the substitution of Ni 2+ and Mn 2+ ions into the Zn 3 P 2 lattice, the magnetic property in the samples is caused by the exchange interaction between local spin-polarized electrons (like the electrons of Ni 2 P and Mn 3 P 2 ions) and the conductive electrons.Conductive electrons may become spin-polarised as a result of such contact.As a result, the local spin-polarized electrons of other Ni and Mn ions interact with the spin-polarized conductive electrons through an exchange interaction.The transition elements Ni (2.80-3.50μB) and Mn (5.32-6.10μB) will have an effective magnetic moment was seen experimentally reported [37].Zeppenfeld et al [38] discussed Ni 2 P compounds were seen as a paramagnetic behavior at 2 K to 300 K and reported that Ni 2 P compounds show high nickel content.Mn 3 P 2 does not have experimental results was found.But maybe be the best of our knowledge Mn (0.01,0.03,0.05 and 0.07) has the most effect on ferromagnetism due to more dopant concentration.
Figure 9(c) shows the room-temperature ferromagnetism for Ni-Mn codoped samples in the field range of +400 Oe.At Z-1 samples exhibited the highest coercivity is 128.680Oe and the Z-4 sample exhibited low coercivity is 57.820Oe.Maybe the best of our knowledge, from the SEM analysis diameter of the particles increases and this produce a decrease in the coercive field were seen in figure 9(c).M-H loop clearly shows coercivity and retentivity.Retentivity increased with increasing dopant concentration from Z-1 (0.0031 emu g −1 ) to Z-3 (0.0064 emu g −1 ) sample and the retentivity decreased with increasing higher dopant concentration (Z-4) were clearly observed in figure 9(c).The strength of the magnetic moment depends on dopant concentration and applied magnetic field.According to the hysteresis loop it can be concluded that the ferromagnetism developed with increased dopant level and it changes from weak ferromagnetism to ferromagnetism in Z-1 to Z-4 samples.Based on this loop the obtained saturation magnetization, coercivity, and retentivity with Ni-Mn concentration are mentioned in table 2.

Conclusion
We have successfully synthesized Zn (3-(x+y)) Ni x Mn y P 2 nanoparticles at x = Ni = 0.02, y = Mn = 0.01, 0.03, 0.05, and 0.07 using the solid-state reaction method.The x-ray diffraction results confirmed that all codoped samples exhibited a tetragonal structure.The observed diffraction peak (4 0 0) indicates that the lattice parameters decrease with increasing dopant concentration.The surface morphological images confirm that the increase in the dopant concentration leads to an increase in the diameter of the nanoparticles.EDAX spectra confirmed that the Ni-Mn were properly doped in pure lattice and expected near atomic ratio was formed.Maximum reflectance exhibited pure lattice and synthesized samples exhibited less reflectance and the optical band gap increases from 1.410 eV to 1.455 eV with increasing dopant content.The photoluminescence spectra of undoped and codoped samples exhibited the same emission peak position and PL intensities increased due to the dopant concentration.VSM reveals information about the room temperature ferromagnetism ordering in the undoped lattice and codoped samples confirming that weak ferromagnetism to ferromagnetism with higher dopant concentration (Z-4 sample).

Figure 1 .
Figure 1.XRD patterns of undoped lattice and Ni-Mn co-doped Zn 3 P 2 nanoparticles in the 2θ range of 20°to 90°.

Figure 8 .
Figure 8. PL emission spectra of (a) undoped lattice and Ni-Mn codoped nanoparticles with excitation at 244 nm and (b) with excitation at 195 nm.

Figure 9 .
Figure 9. (a) Room temperature M-H curves for undoped and (b) Ni-Mn codoped samples in the field range of −15000 Oe to +15000 Oe and (c) field range of −400 Oe to +400 Oe.