Solid State Communications 141 (2007) 22–24www.elsevier.com/locate/ssc

Magnetic properties of the quasi-one-dimensional system BaMn2V2O8

Zhangzhen Hea,b,∗, Yutaka Uedaa, Mitsuru Itohb

a Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japanb Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan

Received 20 September 2006; accepted 23 September 2006 by A.H. MacDonaldAvailable online 11 October 2006

Abstract

Magnetic properties of BaMn2V2O8 are investigated by means of susceptibility, magnetization, and heat capacity measurements. Ourexperimental results show that BaMn2V2O8 is a one-dimensional canted antiferromagnet. The antiferromagnetic transition at a relatively highTN of 37 K may be due to an enhancement of interchain interaction in the system, since Mn2+ ions have large spin moment of S = 5/2. Weakferromagnetism in BaMn2V2O8 may be due to Dzyaloshinskii–Moriya interactions arising from its noncentrosymmetric crystal structure.c© 2006 Elsevier Ltd. All rights reserved.

PACS: 75.50.-y; 75.30.Et; 75.10.Jm

Keywords: A. BaMn2V2O8; A. Vanadates; D. One-dimensional systems; D. Canted antiferromagnet

1. Introduction

One-dimensional (1D) magnetic systems have been activelystudied in solid state physics, due to the discovery of variousinteresting magnetic properties. Compounds with a formulaof AM2V2O8 (A = Ba, Sr, Pb; M = Cu, Co, Ni, Mn)[1–6] have attracted much attention due to their peculiar crystalstructures. As shown in Fig. 1, all magnetic M2+ ions areequivalent with the arrays of edge-shared MO6 octahedraforming screw chains along the c-axis, and the screw chainsare separated by nonmagnetic VO4 (V5+) tetrahedral and A2+

ions, resulting in a quasi-1D structural arrangement. Recently,we found that although AM2V2O8 compounds have similarcrystal structures, their magnetic behaviors are clearly different,depending on different magnetic ions in the systems. Forexample, BaCu2V2O8 (S = 1/2) is a 1D alternating spinchain system with a large spin gap of ∼230 K [7,8] andPbNi2V2O8 (S = 1) is a typical 1D Haldane spin-gapsystem [5], while BaCo2V2O8 and SrCo2V2O8 (S = 3/2) are1D Ising spin systems with large magnetic anisotropy [9–12].

BaMn2V2O8 is a member of the AM2V2O8 system, whichhas a tetragonal structure of space group I 41cd with a =

∗ Corresponding author at: Institute for Solid State Physics, University ofTokyo, Kashiwa 277-8581, Japan. Tel.: +81 4 7136 3436; fax: +81 4 7136 3436.

E-mail address: he@issp.u-tokyo.ac.jp (Z. He).

0038-1098/$ - see front matter c© 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.ssc.2006.09.043

Fig. 1. (Color online) Crystal structure of AM2V2O8 (A = Ba, Sr, Pb;M = Cu, Co, Ni, Mn). Octahedra, tetrahedra, large ball and small ball representMO6, VO4, A, and O, respectively.

12.267(1) A and c = 8.424(1) A [6]. In this paper,we first report the magnetic properties of BaMn2V2O8 bymeans of magnetic susceptibility, magnetization and heatcapacity measurements, and discuss the nature of the magneticbehaviors.

2. Experimental

A polycrystalline sample was synthesized by a standardsolid state reaction method using a mixture of high purityreagents BaCO3 (4N), MnC2O4 · 2H2O (3N), and V2O5 (4N)

as the starting materials in the molar ratio of 1:2:1. The

Z. He et al. / Solid State Communications 141 (2007) 22–24 23

mixture was ground carefully, homogenized thoroughly withethanol (99%) in an agate mortar, and then packed into analumina crucible and calcined at 930 ◦C in an Ar flow for60 h with several intermediate grindings. Finally, the productwas pressed into pellets and sintered at 950 ◦C for 20 h, andthen cooled to room temperature at a rate of 100 ◦C/h. Noimpurity phase was observed from powder X-ray diffraction(XRD) measurements using Cu Kα radiation. The structuralparameters were refined by the Rietveld method using theRIETAN-2000 program [13], being in good agreement withthose reported previously [6]. The magnetic measurementswere performed using a superconducting quantum interferencedevice (MPMS5S, Quantum Design) magnetometer and theheat capacity was measured by a relaxation method using acommercial physical property measurement system (PPMS,Quantum Design).

3. Results and discussion

The temperature dependences of the magnetic susceptibilityof polycrystalline BaMn2V2O8 are shown in Fig. 2. Thesusceptibility increases with decreasing temperature, whilea broad maximum is observed around 170 K, showing acharacteristic feature of 1D magnetism. A rapid increase insusceptibility is seen below 46 K, suggesting the developmentof ferromagnetic correlation. Different histories are seen below37 K in the field cooled (FC) and zero-field cooled (ZFC)regimes. Such irreversibility is a characteristic behavior offerromagnetic ones. The ferromagnetic moment is roughlyestimated to be ∼0.0045µB/Mn2+ in a field of 1000 Oe,which corresponds to ∼0.09% of the full Mn2+ ions(S = 5/2) moments, suggesting that the system is acanted antiferromagnet. The inset of Fig. 2 shows that thesusceptibility above 170 K can be fitted well using 1D spin-5/2 linear chain model [14,15] with J/kB = −11.03 K andg = 2.33. The value of g-factor obtained is somewhat largerthan that of the spin only, indicating that the real system is notregarded as an isolated linear chain system. Actually the systemfalls into a three-dimensional magnetic ordered ground state ata relatively high temperature.

The magnetization (M) as a function of the applied field(H) at 5 K is shown in Fig. 3. Clear hysteresis and remnantmagnetization near H = 0 are observed, evidencing aferromagnetic component in the system. The linear behavior ofthe magnetization is seen above H of 1 T and no magnetizationsaturation is seen up to 5 T. These behaviors are alsocharacteristic features of a canted antiferromagnet, which arein good agreement with susceptibility data. The results of heatcapacity measurements for H = 0 are shown in Fig. 4. Thereis a slight jump at 46 K, followed by a clear sign of a λ-likefeature at around 37 K, agreeing with the susceptibility data.This indicates that a long-range magnetic ordering (LRO) startsat 46 K and completes in a canted antiferromagnetism at 37 K.The entropy change for this λ-like anomaly is roughly estimatedto be ∆S = ∼0.12 J/mol K, which corresponds to 0.84% ofR ln(2S + 1) expected for spin-5/2 systems. This is becausethe magnetic entropy is lost over a very wide temperature range,

Fig. 2. (Color online) Magnetic susceptibility of polycrystalline BaMn2V2O8.The inset shows a broad maximum around 170 K. The solid line is a fit basedon a 1D S = 5/2 linear chain model [14,15].

Fig. 3. Magnetization as a function of applied field H at 5 K.

Fig. 4. Heat capacity measured in zero magnetic field.

that is, most of the entropy of the system has been lost throughthe short-range magnetic correlation seen at ∼170 K.

Our experimental results of susceptibility, magnetization andheat capacity measurements clearly show that BaMn2V2O8 isa quasi-1D spin-5/2 canted antiferromagnet. It is well knownthat an ideal 1D spin chain compound does not show LROabove T = 0 K due to strong quantum spin fluctuation;

24 Z. He et al. / Solid State Communications 141 (2007) 22–24

however, almost all quasi-1D compounds display LRO attheir ground states due to weak interchain interaction [16].Therefore, magnetic ground states in 1D spin chain compoundsare likely determined by the competition between spinfluctuation and interchain interaction, that is, the decreaseof spin fluctuation due to increasing spin moment and theenhancement of interchain interaction should lead to LRO in thesystems. The different magnetic ground states in isostructuralcompounds: BaCu2V2O8 (S = 1/2,∆ = ∼230 K),PbNi2V2O8 (S = 1,∆ = ∼40 K), BaCo2V2O8 (S = 3/2,

TN = ∼5 K) and BaMn2V2O8 (S = 5/2, TN = ∼37 K)

can be interpreted through the competition mentioned above,with increasing spin moment in the systems. Further, anenhancement of interchain interaction corresponding to highTN in BaMn2V2O8 is also observed with substitution ofMn2+ (S = 5/2) for Co2+ (S = 3/2) in BaCo2V2O8.In addition, weak ferromagnetism in BaMn2V2O8 may bedue to Dzyaloshinskii–Moriya (DM) interactions [17,18]arising from the noncentrosymmetric crystal structure ofBaMn2V2O8 (I 41cd) as seen in SrCo2V2O8. In order to clarifythe magnetic nature of BaMn2V2O8, growth of large singlecrystals with good quality is now in progress.

4. Conclusions

Polycrystalline samples of BaMn2V2O8 with good qualityhave been synthesized by a standard solid state reactionmethod. Susceptibility, magnetization and heat capacitymeasurements show that BaMn2V2O8 is a quasi-1D spin-5/2canted antiferromagnet. The relatively high antiferromagnetictransition temperature around 37 K may be due to the decreaseof spin fluctuation or enhancement of interchain interaction

in the system, since Mn2+ ions have a large spin momentof S = 5/2. The weak ferromagnetism could arise from theDM interactions attributed to the noncentrosymmetric crystalstructure of BaMn2V2O8.

Acknowledgment

One of the authors (Z.H.) acknowledges the Japan Societyfor the Promotion of Science (JSPS) for awarding a ForeignerPostdoctoral Fellowship (P06047).

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