## Lattice, Magnetic, and Electronic Transport Properties in Antiperovskite M3AX Compounds

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# Synthesis, Magnetization, and Electrical Transport Properties of Mn_{3}Zn_{0.9}Cu_{0.1}N

**Academic Editor:**Y. Sun

#### Abstract

We synthesized Mn_{3}Zn_{0.9}Cu_{0.1}N by solid state reaction, and magnetic as well as electrical transport properties were investigated. It is found that Mn_{3}Zn_{0.9}Cu_{0.1}N exhibits a first-order antiferromagnetism (AFM) to paramagnetic (PM) transition with the Néel temperature ~163 K, and substitution of Cu for Zn would favor ferromagnetism (FM) state and weaken AFM ground state, leading to a convex curvature character of curve. With high external fields 10 kOe–50 kOe, magnetic transition remains a robust AFM-PM feature while FM phase is completely suppressed. Thermal hysteresis of under 500 Oe is also suppressed when the magnetic field exceeds 10 kOe. Mn_{3}Zn_{0.9}Cu_{0.1}N exhibits a good metallic behavior except for a slope change around , which is closely related to AFM-PM magnetic transition. Compared with the first differential of resistivity with respect to temperature for in transition temperature range, the absolute value of is much lower which is close to zero.

#### 1. Introduction

The Mn-based antiperovskite compounds Mn_{3}XN (X = Cu, Zn, Ga, Sn, and so on) have attracted considerable attentions because of the discoveries of interesting properties such as non-Fermi liquid behavior [1, 2], magnetoresistance [3, 4], negative thermal expansion (NTE) [5–7], zero thermal expansion (ZTE) [8, 9], spin-glass behavior [10], and large negative magnetocaloric effect (MCE) [11–14].

As a typical member of Mn_{3}XN, Mn_{3}ZnN has been intensively investigated, and some novel properties have been observed like unusual phase separation and resistive switching phenomenon around antiferromagnetism (AFM) to paramagnetic (PM) transition [15, 16]. More interestingly, it has been confirmed that properties of Mn_{3}ZnN can be sensitively influenced by partial substitution at Zn sites, 1*a *(0,0,0) by other elements or even vacancies. For example, Sun et al. found that an obvious NTE phenomenon appears in Mn_{3}Zn_{0.5}Ge_{0.5}N and ZTE behavior in Mn_{3}Zn_{0.7}Sn_{0.3}N, while abrupt lattice contraction near magnetic transition does not appear in Mn_{3}ZnN [17]. Very recently, Wang et al. demonstrated that NTE features in Mn_{3}Zn_{x}N can be induced and tuned by modulating the Zn occupancy [9].

It is of great interests to further probe the intrinsic relation between properties and substitution element or , at 1*a *(0,0,0) sites, and understanding the novel properties origin is useful in attaining new insight on the magnetic mechanism in such a strong related system. All these make the further extensive experimental investigations on Mn_{3}ZnXN highly desirable for solving these puzzles. To this end, we choose Cu element as another attempt to address this issue. In this paper, we synthesized Mn_{3}Zn_{0.9}Cu_{0.1}N by solid state reaction and magnetic, electrical transport properties were investigated. It is found that Mn_{3}Zn_{0.9}Cu_{0.1}N exhibit a typical AFM-PM transition with the Néel temperature of ~163 K. Substitution of Cu for Zn favors FM state and weakens AFM ground state in Mn_{3}Zn_{0.9}Cu_{0.1}N. Under high external fields (10 kOe–50 kOe), AFM-PM transition feature remains robust where FM phase is completely suppressed. Further, Mn_{3}Zn_{0.9}Cu_{0.1}N exhibits a good metallic behavior except for a slope change around and shows a normal Fermi liquid behavior in a low temperature range from 5 K to 80 K. While compared with in transition temperature range, the absolute value of is much lower and is close to zero.

#### 2. Experiment

Sintered polycrystalline samples of Mn_{3}Zn_{0.9}Cu_{0.1}N were prepared by a solid state reaction. Mn_{2}N (homemade, 99.9%), and high purity Zn (Alfa, 99.99%), high purity Cu (Alfa, 99.99%) were mixed in the stoichiometric proportion and pressed into a pellet. The pellet was wrapped by tantalum foil and placed into a quartz tube and then was vacuumized to Pa. The quartz tube was sealed and heated at 850°C for 96 h. The as-synthesized sample was characterized by high-resolution X-ray diffraction diffractometer (XRD, Philips X’PERT MPD) with cell parameter calculated from Rietveld analysis of XRD pattern *a* = 3.89965 Å, space group *Pm3 m*. It is less than that of Mn_{3}ZnN (ICDD-PDF: 23–0229, space group *Pm3 m*). Magnetization measurements were performed with a commercial superconducting quantum interference device (SQUID). Both field-cooled (FC) and zero-field-cooled (ZFC) magnetizations were measured from 10 K to 300 K. The resistivity was measured using the standard four-probe technique in a physical property measurement system (Quantum Design, PPMS).

#### 3. Results and Discussion

Temperature dependence of magnetization measured in both FC and ZFC of Mn_{3}Zn_{0.9}Cu_{0.1}N is shown in Figure 1. A clear AFM-PM transition can be seen in both sets of data around the Néel temperature ~163 K, although obtained in the FC cycle shifts to a lower temperature from ZFC cycle by about 8 K. The thermal hysteresis in curves, particularly near , implies a first-ordered magnetic transition in Mn_{3}Zn_{0.9}Cu_{0.1}N. Similar result has been observed in Mn_{3}ZnN by Kim et al. [18]. With decreasing the temperature, as shown in the inset, the absolute value of decreases near from emu/(gK) to emu/(gK) and curve shows an abnormal convex curvature from 125 K to 25 K, indicating an existence of FM state at low temperature. This result should be ascribed to the substitution of Cu in Mn_{3}Zn_{0.9}Cu_{0.1}N. It is well known that FM phase in low- region is intrinsic property of Mn_{3}CuN [19, 20], thus Cu doping in Mn_{3}Zn_{0.9}Cu_{0.1}N would favor FM state and weaken AFM ground state, and curve correspondingly exhibits a convex curvature character.

Figure 2 presents the temperature dependence of magnetization measured at several magnetic fields (10 kOe, 20 kOe, 30 kOe, 40 kOe, and 50 kOe). It can be seen that AFM-PM transition always located near of ~163 K under different external fields, while the FM phase (as shown in Figure 1) has been completely suppressed beyond 10 kOe, implying that below , the AFM phase is relatively robust while FM phase is metastable in this case. Further, it is worthy to note that the thermal hysteresis of curves displayed in Figure 1 is also suppressed when the magnetic field exceeds 10 kOe. It can be seen that magnetization is not saturated even when the external field exceeds 50 kOe; to demonstrate this feature clearly, magnetization versus magnetic field ( versus ) around is plotted in Figure 3, and the isotherms curves are nearly linear with increasing of .

Figure 4 illustrates the temperature dependence of resistivity of Mn_{3}Zn_{0.9}Cu_{0.1}N from 10 K to 300 K under 0 kOe, 10 kOe, and 50 kOe, respectively. Mn_{3}Zn_{0.9}Cu_{0.1}N exhibits a typical metallic behavior except for a slope change around 162 K, which is closely related to AFM-PM transition, similar phenomena have been observed in other systems [21], where decreases due to the orientation of magnetic moments from AFM ordering. However, no magnetoresistance appears during the whole temperature ranges in this study. Simultaneously, we note that the absolute value of in the transition temperature range of 140 K–162 K nearly decreases to zero, as shown in the bottom inset of Figure 4, which is lower than that of Mn_{3}ZnN as reported in [6]. Previous investigations have shown that there exists an unusual conduction property, namely, low temperature coefficient of resistivity (TCR) in Mn_{3}CuN above magnetic transition temperature; that is, the absolute value of is close to zero in this temperature range [22]. Moreover, in [23] it is assumed that Cu–N bonds serve as the key role to induce low TCR feature in nitrides. Therefore, it is reasonable to suggest the plateau-like curve around in Mn_{3}Zn_{0.9}Cu_{0.1}N could be well understood in terms of partial doping effect induced by Cu. The top inset in Figure 4 shows a linear relationship between and below 80 K, which agrees well with the following equation:
where is residual resistivity and is constant; this result implys a Fermi liquid behavior that exists in Mn_{3}Zn_{0.9}Cu_{0.1}N in temperature range [1]. In this sense, we assumed that the electron-electron scatterings are dominant in this temperature range. However, with temperature increasing, the number of phonon sharply increases and phonon scatterings enhance accordingly, as one can see in temperature range and linear relationship between - indicates that electron-phonon scatterings exceed electron-electron scatterings in the temperature ranges mentioned above.

#### 4. Conclusion

In summary, we synthesized Mn_{3}Zn_{0.9}Cu_{0.1}N by solid state reaction, and magnetic as well as electrical transport properties were investigated. It is found that Mn_{3}Zn_{0.9}Cu_{0.1}N exhibits a first-ordered antiferromagnetism (AFM) to paramagnetic (PM) transition with the Néel temperature ~163 K, and substitution of Cu for Zn would favor FM state and weaken AFM ground state, leading to a convex curvature characterof curve. Further, we found that under high external fields 10 kOe–50 kOe magnetic transition remains a robust feature of AFM-PM while FM phase is completely suppressed. Further, thermal hysteresis of exhibited at 500 Oe is also suppressed when the magnetic field exceeds 10 kOe. Mn_{3}Zn_{0.9}Cu_{0.1}N exhibits a good metallic behavior except for a slope change around , which is closely related to AFM-PM magnetic transition. Compared with first differential of resistivity with respect to temperature for Mn_{3}ZnN in transition temperature range, the absolute value of is much lower and is close to zero.

#### Acknowledgments

This work is supported financially by the National Natural Science Foundation of China (Grant no. 50902037, 51172055, 51172193, 50902014, and 51072226), fundamental Research Funds for the Central University (Grant no. HIT.BRETIII.201220, HIT, NSRIF.2012045, and HIT.ICRST.2010008), the Foundation of National Key Laboratory of Science and Technology on Advanced Composite in Special Environment in HIT, and International Science and Technology Cooperation Program of China (2012DFR50020).

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Copyright © 2013 Y. Yin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.