A ferromagnetic-like phase transition in new oxychalcogenide HgOCuSe
aa r X i v : . [ c ond - m a t . s t r- e l ] M a y A ferromagnetic-like phase transition in new oxychalcogenideHgOCuSe
G. C. Kim, ∗ M. Cheon, I. S. Park, D. Ahmad, and Y. C. Kim Department of Physics, Pusan National University, Busan 609-735, Korea (Received)
Abstract
We report the synthesis of a new oxychalcogenide HgOCuSe sample. The resistivity decreasesas a function of T . with decreasing temperature from room temperature down to around 80 K.There exists a very sharp ferromagnetic-like phase transition at around 60 K under a field of H =100 Oe. Contrary to the usual ferromagnetic materials, the descending and ascending branches ofthe magnetic hysteresis curve, at 30 K, are reversed in the whole irreversible field range and thereverse irreversibility decreases at 5 K.PACS numbers : 75.20.En, 75.47.Np, 75.60.Ej ∗ Electronic address: [email protected] p -type semiconductor with the positive Seebeckcoefficient and the band gap, estimated from an optical measurement, is about 0.8 eV [1].The temperature dependence of the electrical resistivity of BiOCuSe exhibits a broad peakat 250 K [2]. In the case of BiOCuTe, the electrical resistivity shows a metallic temperaturedependence, which may be caused by the shallow valence band maxima of Te [1].LaOCuSe is also a p -type semiconductor with a wide band gap ( E g = 2.8 eV) [3]. Thus,LaOCuSe was studied as a candidate for dilute magnetic semiconductors. The hole con-centration of LaOCuSe increases up to 2.2 × cm − by doping La with Mg [4]. It wasexpected that the doping of LaOCuSe with a magnetic ion would induce high temperaturehole-mediated ferromagnetism. However, Mn-doped LaOCuSe did not show ferromagnetism,which may be caused by the low solubility limit of Mn doping.In this brief report, we report the synthesis of a new oxychalcogenide HgOCuSe sample.The resistivity for HgOCuSe decreases as a function of T . until the magnetic phase tran-sition occurs. The ferromagnetic-like phase transition occurs around 60 K under H = 100Oe. The descending and ascending branches of the isothermal magnetic hysteresis curve, at T = 30 K, are reversed in the whole irreversible field range.We synthesized a polycrystalline HgOCuSe sample by the conventional solid state reac-tion. A pellet of total weight 1 g of the appropriate ratio of the mixtures of HgO (Junsei99.5 %), CuSe (Alfa Aesar 99.5 %), and Se (Alfa Aesar 99.999 %) powders was heated inan evacuated quartz tube of the length 10 cm at 455 o C for 50 hr. The 10 % of Se wasadded to compensate for the loss of Se by the low melting point (210 o C) during the heattreatment. After the heat treatment, we found several little liquid Hg drops inside thequartz tube. The X-ray diffraction (XRD) pattern on the powdered sample was measuredat a 2 θ range from 4 o to 60 o by using the Cu K α radiation. The electrical resistivity wasmeasured by the standard four probe method at the current of 1 mA from 300 to 30 K. Thetemperature dependence of magnetization was measured under H = 100 Oe and 10 kOeby a superconducting quantum interference device magnetometer. The isothermal magnetichysteresis curves were measured at T = 5 K, 30 K, and 60 K under a field range between -60 kOe and 60 kOe.Figure 1 shows the XRD pattern of the HgOCuSe powder. The peaks are very sharp,which means that our sample is well crystallized. HgOCuSe has the same tetragonal struc-ture as BiOCuSe, while the length of the a-axis ( a = 4.31 ˚ A ) of HgOCuSe is longer than2hat ( a = 3.92 ˚ A ) of BiOCuSe, and the length of the c-axis ( c = 6.09 ˚ A ) is shorter than that( c = 8.91 ˚ A ) [5].Figure 2 shows the temperature dependence of electrical resistivity for the polycrystallineHgOCuSe sample measured on cooling. Contrary to the polycrystalline BiOCuSe showinga semiconductive behavior [2], the resistivity for HgOCuSe decreases down to 30 K withdecreasing temperature without any anomaly by a phase transition. The resistivity at 300K for the polycrystalline HgOCuSe sample is about 0.95 mΩ · cm, which is approximatelythree orders of the magnitude smaller than that (1.2 Ω · cm) for the polycrystalline BiOCuSesample [2]. We fitted the resistivity data with an equation ρ ( T ) = ρ + AT n , (1)where ρ is the resistivity at T = 0 K, and A is the coefficient of resistivity relating to theeffective band mass. It is well known that for a material showing the Fermi liquid behavior,the exponent n in Eq. (1) equals to 2 [6]. As shown in the inset of Fig. 2, the resistivity forHgOCuSe is almost proportional to T . except when the temperature is less than around80 K. The red solid line in Fig. 2 represents Eq. (1) with n = 1.75, ρ = 0.403 mΩ · cm, and A = 2.515 × − Ω · cmK − . . The experimental resistivity deviates from the fitted valuebelow around 80 K.Figure 3 shows the temperature dependence of dc magnetization for the polycrystallineHgOCuSe sample under H = 100 Oe at a zero field cooling (ZFC) and field cooling (FC)mode. It is evident from Fig. 3 that there exists a very sharp ferromagnetic-like phasetransition around T = 60 K. The magnetization value at 5 K on the FC mode is about 10% larger than that on the ZFC mode. It should be noted that a weak shoulder feature ofmagnetization of both of ZFC and FC modes is seen close to the transition temperature.Below 30 K, the ZFC and FC magnetizations retain a constant, temperature independentvalue. The inset of Fig. 3 shows the temperature dependence of an inverse magnetizationfor the polycrystalline HgOCuSe sample, which is measured under H = 10 kOe. For aferromagnetic material, the susceptibility χ ( T ) in the paramagnetic region above the Curiepoint is described by the Curie-Weiss law, χ ( T ) = CT − Θ , (2)where C is the Curie constant and Θ is the Weiss temperature [7]. For the polycrystallineHgOCuSe sample, C and Θ are 8.2 × − emu · K/g · Oe and 80 K, respectively. As shown3n the inset of Fig. 3, the temperature range showing a linear inverse magnetization is verynarrow, which means the absence of local moments.We plot the isothermal magnetic hysteresis curves for the polycrystalline HgOCuSe sam-ple at T = 5, 30, and 60 K in Fig. 4 (a). As shown, the magnetization saturates around H = 1 kOe for T = 5 and 30 K and the saturation magnetization decreases with increasingtemperature. We confirmed that the magnetic hysteresis curve at T = 60 K exhibits aparamagnetic-like behavior without saturation magnetization up to 60 kOe and is almostreversible for the whole measuring field range as shown in Fig. 4 (d).Figure 4 (c) shows the magnification of the hysteresis curve at T = 30 K for a fieldrange between 0 Oe and 1.1 kOe. We plot only half of the hysteresis curve to show theirreversibility more clearly. Although the hysteresis width is very narrow as shown in Fig.4 (c), the irreversibility is sustained for a wide field range between -1 kOe and 1 kOe.Generally, for the hysteresis curve of a ferromagnetic material, the magnetization values forthe descending branch from a positive high field are larger than those for the ascendingbranch from a negative high field, under the same field at a specific temperature, and theirreversibility increases with decreasing temperature [8]. The black (red) solid line in the(b), (c), and (d) in the Fig. 4 corresponds to the descending (ascending) branch of thehysteresis curve. However, the isothermal magnetic hysteresis curves for the polycrystallineHgOCuSe sample at T = 30 K are reversed in the whole irreversible field range, that is,the magnetization values for the ascending branch are larger than those for the descendingbranch. The raw value of the remnant magnetic moment (i.e. the magnetic moment at H = 0 Oe) for the descending (ascending) branch at T = 30 K is -2.78 × − emu (2.85 × − emu) with a standard deviation of 2.64 × − emu (4.69 × − emu). Because the percentageerror for each branch is less than 2 %, our data is reliable.Figure 4 (b) shows the magnification of the hysteresis curve at T = 5 K for a field rangebetween 0 Oe and 1.1 kOe with the same scale as that of Fig. 4 (c). It is interesting that whilethe reversion between the descending and ascending branches at the hysteresis curve stillremains, the width decreases, rather than increases, with decreasing temperature. In orderto evaluate the degree of irreversibility, we obtain the magnitude of the field difference, ∆ H ( ≡ | H + − H − | ) from the hysteresis curves, where H + and H − correspond to the field valuesat M = 0 in the descending and the ascending branches of a hysteresis curve, respectively.While ∆ H at T = 30 K is around 20 Oe, that at 5 K is around 10 Oe. Specifically, the4ysteresis curve at T = 5 K is almost reversible for a field range between 300 (-300) and 650(-650) Oe. We expect that the reversible regime in the isothermal hysteresis curve expandsmore at temperatures lower than 5 K. Consequently, it is likely that the ground state ofHgOCuSe at T = 0 K is a very soft ferromagnetism. We confirmed that our observedreverse hysteresis curves are reproducible for other HgOCuSe samples synthesized underthe same conditions and HgOCu . Se [9] synthesized at a different condition, and is stillsustained after 6 months.In summary, we synthesized a new oxychalcogenide HgOCuSe with unusual magnetichysteresis. The temperature dependence of the resistivity at
T >
80 K is described by thenon-Fermi liquid behavior that the exponent n in Eq. (1) is 1.75. The ferromagnetic-likevery sharp transition occurs around T = 60 K under a field of H = 100 Oe. Thedescending and the ascending branches of the isothermal magnetic hysteresis curve for thepolycrystalline HgOCuSe sample at T = 30 K are reversed in the whole irreversible fieldrange and the reverse irreversibility decreases as temperature decreases.This study was financially supported by Pusan National University in program. Post-Doc. 2010. [1] H. Hiramatsu, H. Yanagi, T. Kamiya, K. Ueda, M. Hirano, and H. Hosono, Chem. Mater. ,326 (2008).[2] T. Ohtani, Y. Tachibana, and Y. Fukjii, J of Alloys and Compounds , 175 (1997).[3] H. Yanagi, S. Ohno, T. Kamiya, H. Hiramatsu, M. Hirano, and H. Hosono, J. Appl. Phys. ,033717 (2006).[4] H. Hiramatsu, K. Ueda, H. Ohta, M. Hirano, T. Kamiya, and H. Hosono, Appl. Phys. Lett. , 1048 (2003).[5] A. M. Kusainova, P. S. Berdonosov, L. G. Akselrud, L. N. Kholodkovskaya, V. A. Dolgikh, andB. A. Popovkin, J Solid State Chem. , 189 (1994).[6] N. W. Aschcroft and I. Mermin, Solid State P hysics , Holt, Rinehart and Winston (1976).[7] C. Kittle,
Introduction to Solid State P hysics , John Wiley (1989).
8] B. D. Cullity,
Introduction to M agnetic M aterials , Addison-Wesley (1972).[9] G. C. Kim, M. Cheon, I. S. Park, D. Ahemad, Y. C. Kim, in preparation. I n t e n s it y ( a r b . un it )
2 (deg.)
FIG. 1: X-ray diffracion pattern on HgOCuSe powder.
50 100 150 200 250 3000.00.20.40.60.81.0 . . ( m c m ) T (K ) ( m c m ) T (K)
Data = +AT FIG. 2: Temperature dependence of resistivity on pollycrystalline HgOCuSe. The inset representsthe resistivity as a function of T . .
20 40 60 80 1000.000.050.100.15
H = 10 kOe M - ( g / e m u ) T (K)
FCZFC H = 100 Oe M ( e m u / g ) T (K)
FIG. 3: Temperature dependence of ZFC and FC magnetization on pollycrystalline HgOCuSeunder H = 100 Oe. The inset shows the temperature dependence of 1/ M on pollycrystallineHgOCuSe under H = 10 kOe. .0 0.5 1.00.00.51.01.5 (c) T = 30 K M ( e m u / g ) H (kOe) M ( e m u / g ) H (kOe) M ( e m u / g ) H (kOe) -10 -5 0 5 10-2-1012 (a) M ( e m u / g ) H (kOe)
FIG. 4: (a) Isothermal magnetic hysteresis curves in a field range between -10 kOe and 10 kOe at T = 5, 30, and 60 K, and magnification of magnetic hysteresis curve in a field range between 0Oe and 1.1 kOe at (b) 5 K, (c) 30 K, and (d) 60 K on pollycrystalline HgOCuSe. The black (red)solid line in the (b), (c), and (d) corresponds the descending (ascending) branch.= 5, 30, and 60 K, and magnification of magnetic hysteresis curve in a field range between 0Oe and 1.1 kOe at (b) 5 K, (c) 30 K, and (d) 60 K on pollycrystalline HgOCuSe. The black (red)solid line in the (b), (c), and (d) corresponds the descending (ascending) branch.