- Email: [email protected]
Magnetization and magnetic susceptibility of kunzite
Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
Magnetization and magnetic susceptibility of kunzite J.A. Bartkowska *, J. Cisowski , J. Voiron, J. Heimann, M. Czaja, Z. Mazurak Institute of Physics, Silesian University of Technology, P.O. Box 221, 40-019 Katowice, Poland Centre of Polymer Chemistry, Polish Academy of Sciences, P.O. Box 20, 41-819 Zabrze, Poland Laboratoire Louis Ne& el, B.P. 166, 38042 Grenoble Cedex 9, France Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland Department of Earth Sciences, Silesian University, ul. Bedzinska 60, 41-200 Sosnowiec, Poland Received 23 May 2000
Abstract We have studied the high-"eld magnetization up to 14.5 T and magnetic susceptibility in the temperature range 1.6}400 K of three di!erent samples of natural kunzite crystals, being a variety of spodumene (LiAlSi O ) and containing transition metal ions. It appears that the total magnetization and susceptibility consist of the paramagnetic contribution following from the temperature-dependent Brillouin-type behavior of magnetic ions and temperature-independent diamagnetic contribution of the spodumene matrix which we have found as being equal to !3.5;10\ emu/g. We have identi"ed the Mn> ions as the dominant ones in the kunzites studied and we have determined the molar concentration of these ions as lying in the range 0.2}0.4%. 2000 Elsevier Science B.V. All rights reserved. PACS: 75.20.!g; 75.20.Ck; 75.30.Cr; 91.60.Pn Keywords: Kunzite; Spodumene; Magnetization; Magnetic susceptibility; Magnetic ion concentration
1. Introduction Kunzite is a natural crystal belonging to the family of spodumenes (LiAlSi O ) which occur in di!erent places of the world, in several varieties with their color depending on kind and quantity of chromatic elements contained in the host matrix. The unit cell of spodumene is monoclinic, space group C (C2/c) with two unequivalent metal ca tion sites M1 and M2 occupied by Al and Li ions, respectively, and these sites may be substitutionally
* Corresponding author. Tel.: #48-32-2552949 ext. 188; fax: #48-32-2561762. E-mail address: [email protected] (J.A. Bartkowska).
replaced by the ions of the transition metal elements, such as Mn, Fe, Cr and the others [1}4]. The colour of natural spodumene crystals can vary from pale mauve-pink for the kunzite variety to a deep green for the hiddenite variety. At room temperature, most spodumenes exhibit strong orange luminescence under electron beam or laser excitation due to the Mn> ions and, when lowering temperature, an additional luminescence emerges which is ascribed to the Cr> ions [4]; however, the optical measurements do not give any quantitative information on the amount of various magnetic ions in the spodumene matrix. One of the methods of determination of small or trace amounts of elements is the X-ray #uorescence (XRF) technique which has been also applied to
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 5 0 7 - 2
274
J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
powdered minerals, including spodumenes [2]. According to this work, both the kunzite and hiddenite varieties studied contain 0.02}0.04 wt% of Mn and the latter contains additionally a similar amount of Fe; the presence of other transition metals has not been detected. In view of the results of luminescence measurements and XRF method, we have undertaken, to our knowledge for the "rst time, the studies of the magnetic properties of natural kunzites of di!erent origin, in order to characterize these minerals in greater detail by a completely di!erent, but complementary and nondestructive method.
2. Experimental We have studied the magnetic properties of three samples of kunzite with various colors and originating from Asia, i.e. sample K1 from Pakistan (lilac), sample K2 from Afghanistan (pink) and sample K3 from Tadjikistan (very light pink). The latter, almost colorless natural crystal has been estimated to contain 0.04 wt% of Mn, while other transition metal elements, such as Cr, V and Co, have not been found as being below the detection limit, i.e. 10 wt ppm approximately [2]. Preliminary results of magnetic measurements performed for this kunzite (K3) have been presented by us in Ref. [5]. The magnetization measurements have been performed at several temperatures between 1.6 and 100 K in DC magnetic "elds up to 14.5 T by the sample extraction method. The magnetization data at a given temperature yield also the magnetic susceptibility which has been derived from the linear part of magnetization. Apart from this, we have carried out careful susceptibility measurements at low "elds (H)0.2 T) with an electronic balance by the Faraday method and in the temperature range 77}400 K. It appears that, even in the case of very low measured signals, both methods give, within the experimental error and taking into account a possible inhomogeneity of samples of minerals studied, similar susceptibility values at the same temperature which is very important from the point of view of reliability of the "nal results.
3. Results and discussion Generally, the magnetic response of the kunzites studied is very weak, in#uencing our approach to analyse the experimental data. Therefore, "rst we will analyze the susceptibility data to obtain the diamagnetic contribution of the spodumene matrix and then we will describe the high-"eld magnetization data which exhibit some scatter. The temperature dependence of the magnetic susceptibility for the kunzite samples studied is presented in Fig. 1. It can be observed that the total measured susceptibility of kunzite decreases quickly with increasing temperature ¹ and approaches zero at higher temperatures indicating that the diamagnetic contribution becomes comparable with the paramagnetic contribution. This is clearly seen in the inset of Fig. 1 showing the total susceptibility as a function of the inverse of temperature in the
Fig. 1. Temperature dependence of the total magnetic susceptibility of three various kunzite samples. Experimental data in the range 1.6}100 K have been determined from the linear part of the magnetization measured by the sample extraction method and the solid curves represent the sum of the Curie and diamagnetic contributions [Eq. (1)]. The inset shows the total susceptibility as a function of the inverse of temperature and the solid straight lines represent the least-squares "tting to the experimental data obtained by the Faraday method in the range 77}400 K.
J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
range 77}400 K which may be approximated by straight lines of the form. C s " #s ¹
(1)
being a sum of the Brillouin-type positive paramagnetic susceptibility of magnetic ions s "C/¹ rep resenting the Curie law with C, the Curie constant and the temperature-independent negative diamagnetic susceptibility s of the host matrix. These lines, "tted to the experimental data for all samples studied, intercept the y-axis close to each other, yielding an average diamagnetic susceptibility of the spodumene matrix s "!3.5;10\ emu/g. On the other hand, the slope of the straight lines gives the Curie constant equal to 9.16, 6.86 and 4.82;10\ K emu/g for samples K1, K2 and K3, respectively. These values of C and s appear to describe also satisfactorily the low-temperature susceptibility data as demonstrated in Fig. 1 by the solid curves. Fig. 2 shows our magnetization data gathered at about 1.6 K at "elds up to 14.5 T for the same three kunzites as in Fig. 1. As can be seen in Fig. 2, for H'6 T, the total magnetization decreases linearly with "eld due to the diamagnetic contribution. We
Fig. 2. Field dependence of the low-temperature total magnetization of the same three kunzite samples as in Fig. 1. The solid curves represent the sum of the paramagnetic Brillouin contribution (denoted by the dotted curves) and diamagnetic contribution. The dashed lines represent extrapolated parts of lowand high-"eld paramagnetic magnetization of sample K1, and intercept (at 1.63 K) near H "1.04 T (the vertical dashed line), corresponding to the Mn> ions S" and g"2.
275
may, therefore, apply our method of analysis of low-temperature magnetization of a paramagnet containing noninteracting magnetic centres [6]. For the kunzites studied, the total magnetization (M ) is then written as M "M B (y)#s H, (2) ( where M "N gk J is the saturation magneti
zation (with N being the number of magnetic ions
per mol, g the LandeH factor, k the Bohr magneton and J the total angular momentum) and B (y) is the ( Brillouin function with y"gk JH/k ¹ (where k is the Boltzmann constant). In the limit of lowand high-"eld magnetization, Eq. (2) reduces to straight lines which intercept at the "eld, 3k ¹ H " , gk (J#1)
(3)
being independent of the magnetic center concentration and giving directly the product g(J#1) characteristic for a given magnetic centre. Applying the above approach to the experimental data shown in Fig. 2, one can see that the extrapolated linear parts of low- and high-"eld magnetization of sample K1, treated as an example, intercept at "elds close to H "1.04 T (the vertical dashed line in Fig. 2), following from the value of the product g(J#1)"7 and corresponding to the spin-only Mn> ion for which J"S" and g"2, where S is the total spin momentum. Having veri"ed that in kunzites studied we are dealing with Mn> ions as the dominant ones and taking s "!3.5;10\ emu/g, found from the data of Fig. 1, we have "tted the total magnetization to Eq. (2), as shown by solid curves in Fig. 2. The paramagnetic Brillouin-type magnetization is represented by dotted curve, and the values of saturation magnetization M , found from the "tting procedure, are equal to 0.584, 0.462 and 0.310 emu/g for samples K1, K2 and and K3, respectively. Finally, Fig. 3 shows the magnetization data gathered at several temperatures between 1.6 and 100 K for sample K1, treated once again as an example. Using the value of M "0.584 emu/g as determined from the results of Fig. 2 for sample K1 along with s "!3.5;10\ emu/g found from
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J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
the susceptibility data of Fig. 1, we have calculated the magnetization at higher temperatures (solid curves in Fig. 3) which appears to describe satisfactorily all the experimental data. For isolated Mn> ions with S" and g"2, we can determine their molar concentration x"N /N (with N being the Avogadro number)
either from the value of the saturation magnetization (x ) or from the Curie constant (x ) which + ! (in emu/g) are equal to
their colour changing from lilac through pink to almost colourless, very light pink. As for sample K3, our result can be converted to the weight percentage x "xm /m (where m is the atomic + + mass of Mn) giving x "0.068 wt% which is com parable with that obtained by XRF method (0.04 wt% [2]), keeping in mind its complexity and a possible inhomogeneity of Mn distribution in the investigated mineral. As can be seen from Figs. 1}3, the calculated curves describe quite well the experimental data for all the kunzites studied, indicating the typical, temperature-dependent Brillouin-type paramagnetic character of the dominant Mn> ions embedded in the spodumene matrix. On the other hand, we do not observe any contribution of Cr> ions (yielding the luminescence emission below 100 K [4]) to the measured magnetization and susceptibility. This follows from (i) a very low Cr concentration (10 wt ppm, being an approximative detection limit of the XRF method [2], corresponds to the molar percentage 0.0036% which is about three times smaller than the absolute precision of magnetic results estimated as 0.01%) and (ii) the fact that Cr> ions with S" exhibit, similarly like Mn> ions, the Brillouin-type paramagnetic behavior of magnetization which, as not containing a positive linear van Vleck-type contribution, saturates at low temperatures and at high "elds [7].
x N M " + gk S m
4. Conclusions
Fig. 3. Field dependence of the total magnetization of the kunzite sample of K1 at di!erent temperatures. The solid curves represent the sum of the paramagnetic Brillouin and diamagnetic contributions [Eq. (2)], calculated with M "0.584 emu/g and s "!3.5;10\ emu/g.
(4)
and x N (gk ) C" ! S(S#1), 3k m
(5)
respectively, where m is the molar mass. Using these formulae for kunzites studied, we get x "0.389, + 0.308, 0.207% and x "0.389, 0.291, 0.205% for ! samples K1, K2 and K3, respectively, which are in very good agreement to each other, bearing in mind small measured signals, possible presence of trace amounts of other magnetic ions and uncertainty of "tting procedures. Thus, we can admit that the Mn concentration in the kunzites studied varies from 0.39% in sample K1, through 0.30% in sample K2 to 0.21% in sample K3 which is indeed re#ected by
Studies of the magnetic properties of three kunzites of di!erent colors and originating from various places of Asia have shown that all the natural crystals studied behave like paramagnetic materials and their total magnetic susceptibility and magnetization is a sum of the positive temperature-dependent Brillouin-type contribution of dominant Mn> ions, as veri"ed by our approach to the low-temperature magnetization, and negative temperature-independent diamagnetic contribution of the spodumene matrix. The analysis of the experimental data has allowed us to determine the diamagnetic susceptibility of spodumene s "!3.5;10\ emu/g and the molar concentra tion of Mn> ions changing from 0.39% in the lilac
J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
kunzite originating from Pakistan (sample K1), through 0.30% in the pink kunzite from Afghanistan (sample K2) to 0.21% in the very light pink kunzite from Tadjikistan (sample K3). Summarizing, our present investigations of natural kunzite crystals together with the previous analysis devoted to diluted magnetic semiconductors [6] show that careful magnetic measurements can be indeed treated as an e$cient and nondestructive method to characterize various paramagnetic materials containing small amounts of magnetic centers.
277
References [1] F. Holuj, Canad. J. Phys. 46 (1968) 287. [2] J. Jurczyk, F. Buhl, R. Sitko, M. Fabis, M. Czaja, Chem. Anal. 42 (1997) 703. [3] A. Manoogian, F. Holuj, J.W. Carswell, Canad. J. Phys. 43 (1965) 2262. [4] G. Walker, A. El Jaer, R. Sherlock, T.J. Glynn, M. Czaja, Z. Mazurak, J. Lumin. 72}74 (1997) 278. [5] J.A. Bartkowska, J. Cisowski, J. Voiron, J. Heimann, M. Czaja, Mineral. Pol. 29 (1998) 45. [6] J. Cisowski, J. Magn. Magn. Mater. 205 (1999) 323. [7] A.H. Morrish, The Physical Principles of Magnetism, Wiley, New York, 1965.
Magnetization and magnetic susceptibility of kunzite J.A. Bartkowska *, J. Cisowski , J. Voiron, J. Heimann, M. Czaja, Z. Mazurak Institute of Physics, Silesian University of Technology, P.O. Box 221, 40-019 Katowice, Poland Centre of Polymer Chemistry, Polish Academy of Sciences, P.O. Box 20, 41-819 Zabrze, Poland Laboratoire Louis Ne& el, B.P. 166, 38042 Grenoble Cedex 9, France Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland Department of Earth Sciences, Silesian University, ul. Bedzinska 60, 41-200 Sosnowiec, Poland Received 23 May 2000
Abstract We have studied the high-"eld magnetization up to 14.5 T and magnetic susceptibility in the temperature range 1.6}400 K of three di!erent samples of natural kunzite crystals, being a variety of spodumene (LiAlSi O ) and containing transition metal ions. It appears that the total magnetization and susceptibility consist of the paramagnetic contribution following from the temperature-dependent Brillouin-type behavior of magnetic ions and temperature-independent diamagnetic contribution of the spodumene matrix which we have found as being equal to !3.5;10\ emu/g. We have identi"ed the Mn> ions as the dominant ones in the kunzites studied and we have determined the molar concentration of these ions as lying in the range 0.2}0.4%. 2000 Elsevier Science B.V. All rights reserved. PACS: 75.20.!g; 75.20.Ck; 75.30.Cr; 91.60.Pn Keywords: Kunzite; Spodumene; Magnetization; Magnetic susceptibility; Magnetic ion concentration
1. Introduction Kunzite is a natural crystal belonging to the family of spodumenes (LiAlSi O ) which occur in di!erent places of the world, in several varieties with their color depending on kind and quantity of chromatic elements contained in the host matrix. The unit cell of spodumene is monoclinic, space group C (C2/c) with two unequivalent metal ca tion sites M1 and M2 occupied by Al and Li ions, respectively, and these sites may be substitutionally
* Corresponding author. Tel.: #48-32-2552949 ext. 188; fax: #48-32-2561762. E-mail address: [email protected] (J.A. Bartkowska).
replaced by the ions of the transition metal elements, such as Mn, Fe, Cr and the others [1}4]. The colour of natural spodumene crystals can vary from pale mauve-pink for the kunzite variety to a deep green for the hiddenite variety. At room temperature, most spodumenes exhibit strong orange luminescence under electron beam or laser excitation due to the Mn> ions and, when lowering temperature, an additional luminescence emerges which is ascribed to the Cr> ions [4]; however, the optical measurements do not give any quantitative information on the amount of various magnetic ions in the spodumene matrix. One of the methods of determination of small or trace amounts of elements is the X-ray #uorescence (XRF) technique which has been also applied to
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 5 0 7 - 2
274
J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
powdered minerals, including spodumenes [2]. According to this work, both the kunzite and hiddenite varieties studied contain 0.02}0.04 wt% of Mn and the latter contains additionally a similar amount of Fe; the presence of other transition metals has not been detected. In view of the results of luminescence measurements and XRF method, we have undertaken, to our knowledge for the "rst time, the studies of the magnetic properties of natural kunzites of di!erent origin, in order to characterize these minerals in greater detail by a completely di!erent, but complementary and nondestructive method.
2. Experimental We have studied the magnetic properties of three samples of kunzite with various colors and originating from Asia, i.e. sample K1 from Pakistan (lilac), sample K2 from Afghanistan (pink) and sample K3 from Tadjikistan (very light pink). The latter, almost colorless natural crystal has been estimated to contain 0.04 wt% of Mn, while other transition metal elements, such as Cr, V and Co, have not been found as being below the detection limit, i.e. 10 wt ppm approximately [2]. Preliminary results of magnetic measurements performed for this kunzite (K3) have been presented by us in Ref. [5]. The magnetization measurements have been performed at several temperatures between 1.6 and 100 K in DC magnetic "elds up to 14.5 T by the sample extraction method. The magnetization data at a given temperature yield also the magnetic susceptibility which has been derived from the linear part of magnetization. Apart from this, we have carried out careful susceptibility measurements at low "elds (H)0.2 T) with an electronic balance by the Faraday method and in the temperature range 77}400 K. It appears that, even in the case of very low measured signals, both methods give, within the experimental error and taking into account a possible inhomogeneity of samples of minerals studied, similar susceptibility values at the same temperature which is very important from the point of view of reliability of the "nal results.
3. Results and discussion Generally, the magnetic response of the kunzites studied is very weak, in#uencing our approach to analyse the experimental data. Therefore, "rst we will analyze the susceptibility data to obtain the diamagnetic contribution of the spodumene matrix and then we will describe the high-"eld magnetization data which exhibit some scatter. The temperature dependence of the magnetic susceptibility for the kunzite samples studied is presented in Fig. 1. It can be observed that the total measured susceptibility of kunzite decreases quickly with increasing temperature ¹ and approaches zero at higher temperatures indicating that the diamagnetic contribution becomes comparable with the paramagnetic contribution. This is clearly seen in the inset of Fig. 1 showing the total susceptibility as a function of the inverse of temperature in the
Fig. 1. Temperature dependence of the total magnetic susceptibility of three various kunzite samples. Experimental data in the range 1.6}100 K have been determined from the linear part of the magnetization measured by the sample extraction method and the solid curves represent the sum of the Curie and diamagnetic contributions [Eq. (1)]. The inset shows the total susceptibility as a function of the inverse of temperature and the solid straight lines represent the least-squares "tting to the experimental data obtained by the Faraday method in the range 77}400 K.
J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
range 77}400 K which may be approximated by straight lines of the form. C s " #s ¹
(1)
being a sum of the Brillouin-type positive paramagnetic susceptibility of magnetic ions s "C/¹ rep resenting the Curie law with C, the Curie constant and the temperature-independent negative diamagnetic susceptibility s of the host matrix. These lines, "tted to the experimental data for all samples studied, intercept the y-axis close to each other, yielding an average diamagnetic susceptibility of the spodumene matrix s "!3.5;10\ emu/g. On the other hand, the slope of the straight lines gives the Curie constant equal to 9.16, 6.86 and 4.82;10\ K emu/g for samples K1, K2 and K3, respectively. These values of C and s appear to describe also satisfactorily the low-temperature susceptibility data as demonstrated in Fig. 1 by the solid curves. Fig. 2 shows our magnetization data gathered at about 1.6 K at "elds up to 14.5 T for the same three kunzites as in Fig. 1. As can be seen in Fig. 2, for H'6 T, the total magnetization decreases linearly with "eld due to the diamagnetic contribution. We
Fig. 2. Field dependence of the low-temperature total magnetization of the same three kunzite samples as in Fig. 1. The solid curves represent the sum of the paramagnetic Brillouin contribution (denoted by the dotted curves) and diamagnetic contribution. The dashed lines represent extrapolated parts of lowand high-"eld paramagnetic magnetization of sample K1, and intercept (at 1.63 K) near H "1.04 T (the vertical dashed line), corresponding to the Mn> ions S" and g"2.
275
may, therefore, apply our method of analysis of low-temperature magnetization of a paramagnet containing noninteracting magnetic centres [6]. For the kunzites studied, the total magnetization (M ) is then written as M "M B (y)#s H, (2) ( where M "N gk J is the saturation magneti
zation (with N being the number of magnetic ions
per mol, g the LandeH factor, k the Bohr magneton and J the total angular momentum) and B (y) is the ( Brillouin function with y"gk JH/k ¹ (where k is the Boltzmann constant). In the limit of lowand high-"eld magnetization, Eq. (2) reduces to straight lines which intercept at the "eld, 3k ¹ H " , gk (J#1)
(3)
being independent of the magnetic center concentration and giving directly the product g(J#1) characteristic for a given magnetic centre. Applying the above approach to the experimental data shown in Fig. 2, one can see that the extrapolated linear parts of low- and high-"eld magnetization of sample K1, treated as an example, intercept at "elds close to H "1.04 T (the vertical dashed line in Fig. 2), following from the value of the product g(J#1)"7 and corresponding to the spin-only Mn> ion for which J"S" and g"2, where S is the total spin momentum. Having veri"ed that in kunzites studied we are dealing with Mn> ions as the dominant ones and taking s "!3.5;10\ emu/g, found from the data of Fig. 1, we have "tted the total magnetization to Eq. (2), as shown by solid curves in Fig. 2. The paramagnetic Brillouin-type magnetization is represented by dotted curve, and the values of saturation magnetization M , found from the "tting procedure, are equal to 0.584, 0.462 and 0.310 emu/g for samples K1, K2 and and K3, respectively. Finally, Fig. 3 shows the magnetization data gathered at several temperatures between 1.6 and 100 K for sample K1, treated once again as an example. Using the value of M "0.584 emu/g as determined from the results of Fig. 2 for sample K1 along with s "!3.5;10\ emu/g found from
276
J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
the susceptibility data of Fig. 1, we have calculated the magnetization at higher temperatures (solid curves in Fig. 3) which appears to describe satisfactorily all the experimental data. For isolated Mn> ions with S" and g"2, we can determine their molar concentration x"N /N (with N being the Avogadro number)
either from the value of the saturation magnetization (x ) or from the Curie constant (x ) which + ! (in emu/g) are equal to
their colour changing from lilac through pink to almost colourless, very light pink. As for sample K3, our result can be converted to the weight percentage x "xm /m (where m is the atomic + + mass of Mn) giving x "0.068 wt% which is com parable with that obtained by XRF method (0.04 wt% [2]), keeping in mind its complexity and a possible inhomogeneity of Mn distribution in the investigated mineral. As can be seen from Figs. 1}3, the calculated curves describe quite well the experimental data for all the kunzites studied, indicating the typical, temperature-dependent Brillouin-type paramagnetic character of the dominant Mn> ions embedded in the spodumene matrix. On the other hand, we do not observe any contribution of Cr> ions (yielding the luminescence emission below 100 K [4]) to the measured magnetization and susceptibility. This follows from (i) a very low Cr concentration (10 wt ppm, being an approximative detection limit of the XRF method [2], corresponds to the molar percentage 0.0036% which is about three times smaller than the absolute precision of magnetic results estimated as 0.01%) and (ii) the fact that Cr> ions with S" exhibit, similarly like Mn> ions, the Brillouin-type paramagnetic behavior of magnetization which, as not containing a positive linear van Vleck-type contribution, saturates at low temperatures and at high "elds [7].
x N M " + gk S m
4. Conclusions
Fig. 3. Field dependence of the total magnetization of the kunzite sample of K1 at di!erent temperatures. The solid curves represent the sum of the paramagnetic Brillouin and diamagnetic contributions [Eq. (2)], calculated with M "0.584 emu/g and s "!3.5;10\ emu/g.
(4)
and x N (gk ) C" ! S(S#1), 3k m
(5)
respectively, where m is the molar mass. Using these formulae for kunzites studied, we get x "0.389, + 0.308, 0.207% and x "0.389, 0.291, 0.205% for ! samples K1, K2 and K3, respectively, which are in very good agreement to each other, bearing in mind small measured signals, possible presence of trace amounts of other magnetic ions and uncertainty of "tting procedures. Thus, we can admit that the Mn concentration in the kunzites studied varies from 0.39% in sample K1, through 0.30% in sample K2 to 0.21% in sample K3 which is indeed re#ected by
Studies of the magnetic properties of three kunzites of di!erent colors and originating from various places of Asia have shown that all the natural crystals studied behave like paramagnetic materials and their total magnetic susceptibility and magnetization is a sum of the positive temperature-dependent Brillouin-type contribution of dominant Mn> ions, as veri"ed by our approach to the low-temperature magnetization, and negative temperature-independent diamagnetic contribution of the spodumene matrix. The analysis of the experimental data has allowed us to determine the diamagnetic susceptibility of spodumene s "!3.5;10\ emu/g and the molar concentra tion of Mn> ions changing from 0.39% in the lilac
J.A. Bartkowska et al. / Journal of Magnetism and Magnetic Materials 221 (2000) 273}277
kunzite originating from Pakistan (sample K1), through 0.30% in the pink kunzite from Afghanistan (sample K2) to 0.21% in the very light pink kunzite from Tadjikistan (sample K3). Summarizing, our present investigations of natural kunzite crystals together with the previous analysis devoted to diluted magnetic semiconductors [6] show that careful magnetic measurements can be indeed treated as an e$cient and nondestructive method to characterize various paramagnetic materials containing small amounts of magnetic centers.
277
References [1] F. Holuj, Canad. J. Phys. 46 (1968) 287. [2] J. Jurczyk, F. Buhl, R. Sitko, M. Fabis, M. Czaja, Chem. Anal. 42 (1997) 703. [3] A. Manoogian, F. Holuj, J.W. Carswell, Canad. J. Phys. 43 (1965) 2262. [4] G. Walker, A. El Jaer, R. Sherlock, T.J. Glynn, M. Czaja, Z. Mazurak, J. Lumin. 72}74 (1997) 278. [5] J.A. Bartkowska, J. Cisowski, J. Voiron, J. Heimann, M. Czaja, Mineral. Pol. 29 (1998) 45. [6] J. Cisowski, J. Magn. Magn. Mater. 205 (1999) 323. [7] A.H. Morrish, The Physical Principles of Magnetism, Wiley, New York, 1965.