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Pressure-induced magnetic transition in MnRhAs
Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
Pressure-induced magnetic transition in MnRhAs N. Fujii *, R. Zach , M. Ishizuka , F. Ono, T. Kanomata, S. Endo Research Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka, 560-8531, Japan Department of Physics, Okayama University, Tsushima-naka, Okayama, 700-8530, Japan Department of Applied Physics, Tohoku Gakuin University, Tagajo, Miyagi, 985-8537, Japan Received 19 September 2000; received in revised form 16 November 2000
Abstract The magnetic properties of a Fe P-type intermetallic compound MnRhAs have been investigated under high pressure up to 8.0 GPa by AC susceptibility measurement. Initially, both the antiferromagnetic (AF(I)) to the canted state magnetic transition temperature ¹ and the canted state to another antiferromagnetic one (AF(II)) transition temper ature ¹ increase with compression. At 4.0 GPa, however, ¹ decreases abruptly, while the increasing rate of ¹ becomes ! ! larger above this pressure. A pressure-induced magnetic phase transition was seen at around this pressure when ¹ and ¹ are plotted in the pressure}temperature phase diagram. The transition from the antiferromagnetic to the ferromag! netic state observed below 160 K with increasing pressure is not frequently observed. 2001 Published by Elsevier Science B.V. PACS: 75.40.Cx; 72.80.Ga; 75.30. Kz; 62.50.#p Keywords: Transition metal compounds; Magnetic properties; Pressure e!ects; Magnetic phase transition; AC susceptibility
1. Introduction The ternary intermetallic compound MnRhAs crystallizes into Fe P-type (hexagonal, P6 2 m) structure with the lattice constants a"6.492 As and c"3.715 As [1]. Mn atoms locate on the pyramidal (3 g) site and Rh atoms on the tetrahedral (3f ) site. In this crystal, Mn and Rh atoms form a layer structure, each Mn layer being separated by a Rh#As atom layer along the c-axis. Therefore, * Corresponding author. Tel.: #81-6-6850-6681; fax: #816-6850-6662. E-mail address: [email protected] (N. Fujii). On leave from Institute of Physics, Technical University of Cracow, 30 084 Krakow, Poland.
MnRhAs is considered to be magnetically nearly two-dimensional. Many studies have been made for this compound because of the wide variety of its interesting magnetic phases depending upon temperature [2}4]. Fig. 1 shows an AC susceptibility vs. temperature curve observed at ambient pressure. The directions of Mn magnetic moments determined by neutron di!raction are also shown in Fig. 1 [5]. The magnetic state below ¹ "160 K is antiferromagnetic AF(I). The coexistence state of the ferromagnetic (F) and the antiferromagnetic components (canted state) appears in the temperature range between ¹ and ¹ "200 K. Another ! antiferromagnetic state which has a di!erent spin structure from AF(I) takes place above ¹ and its ! NeH el temperature is observed at ¹ "240 K [3].
0304-8853/01/$ - see front matter 2001 Published by Elsevier Science B.V. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 3 6 1 - 5
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
13
to 1.5 Gpa [9]. According to them, both ¹ and ¹ increased with pressure and the increasing rate ! of ¹ was larger than that of ¹ . The extrapolation ! of these curves suggested that ¹ and ¹ would ! cross at the point, ¹"240 K and p"2.45 GPa. Above this pressure, the system is expected to be AF(I) or AF(II). The purpose of the present paper is the extension of the pressure dependence of the phase transition temperatures and the investigation of the magnetic structure in the higher-pressure range up to 8 GPa.
2. Experimental procedure
Fig. 1. The upper is temperature dependence of the AC susceptibility of MnRhAs at ambient pressure. The arrows show the directions of the magnetic moment of the Mn layers [5].
MnRhP, having the same crystal structure of Fe P type is ferromagnet with ¹ "401 K and ! with the lattice constants, a"6.226 As and c"3.581 As at ambient conditions [6], both of which are smaller than in MnRhAs. Hence, the magnetic structure of these compounds is considered to be strongly dependent on the lattice constants. The original compound Fe P is well known to have a magnetic phase transition under high pressure [7]. If the lattice constants of MnRhAs were compressed to the values of MnRhP, a transformation state to a ferromagnetic one would be expected. X-ray di!raction measurements for these compounds under high pressure were made by Eto et al. [8]. According to their results, the volume of MnRhAs becomes equal to that of MnRhP at around 20 GPa. They found a structural phase transition from hexagonal to orthorhombic at around 26 GPa. The e!ect of pressure on the magnetic transition temperatures of MnRhAs was investigated by Kanomata et al. up
Polycrystalline samples of MnRhAs were prepared using ceramic method. Original elements were mixed in the desired proportion, sealed in an evacuated silica tube and annealed at about 8503C for 3 days. The sealing and annealing were repeated several times until a good-quality sample was obtained. For each time the crystal structure was investigated by using X-ray powder di!raction technique to ensure the single phase of the Fe P type. High pressure up to 8 GPa was generated by using a multianvil apparatus [10]. The front face of the anvils was a square with 4 mm edge length. To pick up the signal of AC susceptibility, the primary and the secondary coils were wound around the sample with 40 lm wire of Cu coated by polymer insulator. The sample with the pick-up coil system was put into a Te#on capsule together with the pressure medium of Florinate (3 M, FC-77). Finally, the capsule was put in the center of a cubic pressure cell made of pyrophillite. This cubic cell was compressed by six anvils. Before the experiments, the calibration of pressure was made by establishing the relation between the press load and the actual pressure based on the superconducting transition temperature of Pb. A silicon diode was attached to an anvil to detect the temperature. The temperature of the cell was controlled in the temperature range from 4.2 and 380 K using the heater wound around the anvils inside a large cryostat. The highest temperature was limited to 380 K due to the "berglassreinforced plastics adopted for the compression part of this apparatus. The AC magnetic "eld was generated by the primary coil and the signal of AC
14
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
Fig. 2. The AC susceptibility vs. temperature at various pressures up to 8.0 GPa. The ¹ and the ¹ were de"ned as the ! intersects of the baseline and the extrapolations of the peaks.
susceptibility induced in the secondary coil was detected using a lock-in ampli"er. The frequency and the maximum magnitude of the AC magnetic "eld were 990 Hz and 0.5 Oe, respectively.
3. Results and discussion The temperature dependence of the real part of the AC susceptibility s under various pressures up to 8.0 GPa is shown in Fig. 2. The imaginary part was not detected clearly due to the insu$cient S/N ratio. The two magnetic phase transition temperatures ¹ and ¹ were de"ned by Kanomata et al. ! [9] as the intersections of the baseline and the extrapolations of the maximum slopes of the peak at both sides. In this paper we followed this de"nition as shown in Fig. 2. The determination of ¹ became di$cult at pressures higher than ! 7.0 GPa due to the limitation of the measuring temperature range. It was also di$cult to deter-
mine the NeH el temperature ¹ due to its very weak signal in the AF(II) state. Both ¹ and ¹ shifted to higher temperatures ! with increasing pressure up to 4.0 GPa, at which ¹ decreased abruptly and vanished just above 5 GPa. On the other hand, T continued to increase ! with a larger rate. Thus, there is a boundary point at around 4.0 GPa, at which the slope of dT /dp changed ! abruptly and above which the shape of the AC susceptibility vs. temperature curve became ferromagnetic like. The pressure derivative d¹ /dp for ! the lower pressure range up to 4 GPa is 7.7 K/GPa, which is in good agreement with that by Kanomata et al. up to 1.5 Gpa [9]. The pressure derivative of ¹ in the higher pressure range above 4 GPa was ! d¹ /dp"30 K/GPa, which is very large compared ! with any other data previously reported [11] for Fe P-type compounds. The origin of the large pressure derivative of ¹ is probably ascribed to ! the RKKY-type exchange interaction between Mn}Mn atoms along c-axis via a Rh#As layer, which is sensitive to the Mn}Mn distance. Judging from this fact and considering the shape of the s }¹ curves above 5.0 GPa in Fig. 2, it can be concluded that a phase transformation takes place from the complex magnetic state to asimple ferromagnetic one. If the ¹ coalesces with ¹ at around 4}5 GPa, it ! should be considered that there are two kinds of ¹ , below and above this pressure. In the lower ! pressure region, ¹ is de"ned as the transition ! temperature from the canted state to the antiferromagnetic one, and in the higher-pressure region, ¹ is the usual Curie temperature from the fer! romagnetic state to the paramagnetic one. Fig. 3 shows the s }¹ curves in expanded scales under the pressures (a) up to 3.0 GPa and (b) between 3.0 and 4.5 GPa. The "ne steps of pressure were taken in the range 2.0}3.0 GPa so as to observe how ¹ and ¹ became close to each other at ! around 2.5 GPa. The temperature width of the region for the canted state became narrower as the pressure increased up to 3.0 GPa and the peak of AC susceptibility value became weaker. Above 4 GPa the temperature width spread rapidly, and the peak value increased gradually. The p}T phase diagram for MnRhAs determined from the result of the present experiments is shown
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
Fig. 3. The s }¹ curves in expanded scales under the pressures: (a) 1.0, 2.0, 2.3, 2.6 and 3.0 GPa; (b) 3.0, 3.5, 4.0 and 4.5 GPa. Both of the width of the peak and the heights of the intensity decrease up to 3.0 GPa, and then, the width increase rapidly above 4 GPa.
in Fig. 4. There should be a border between the canted state and the ferromagnetic one as shown by the dotted line which was just an extension of the line originally drawn by Kanomata et al. [9]. This magnetic phase diagram is very similar to that of MnRhAs P system at ambient pressure [1,12], \V V when the fraction x is converted to pressure. Similar behavior was also found under pressure in the case of the MnRhAs P series of compounds. \V V Firstly, for the content x"0.4, where the ¹ vari ation vs. external pressure p and vs. chemical substitution x present the same non-linear character [12,14]. Secondly, for the content x"0.5 the pressure-induced ferromagnetic state was experimentally obtained. Those results were con"rmed both by the AC susceptibility and the magnetization measurements carried out under pressure up to 1.5 GPa [12}14]. To determine the magnetic
15
Fig. 4. The p}¹ phase diagram determined from the present experiment. A pressure-induced phase transition from the AF(I) to the F takes place at around 5.0 GPa. ¹ was not detected in this experiment. The dotted line between ¹ and ¹ was drawn ! along extension of Kanomata et al. [9].
phases diagrams more precisely, magnetization measurements in high magnetic "elds and neutron di!raction experiments under high pressure up to at least 6 GPa are necessary.
4. Conclusion By AC susceptibility measurements in MnRhAs under high pressures, it was found that both the magnetic phase transition temperature from antiferromagnetic state (AF(I)) to canted one, ¹ , and from canted state to antiferromagnetic one (AF(II)), ¹ , increased gradually with pressure up to ! 4.0 GPa. Then ¹ decreased suddenly and vanished just above 5 GPa. Above this pressure the system became purely ferromagnetic. This is a new pressure-induced magnetic phase transition from antiferromagnetic to ferromagnetic state. At this phase transition, the pressure derivative of ¹ in! creased suddenly from 7.7 to 30 K/GPa. This value
16
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
is very large compared with the data reported so far for Fe P-type compounds. Acknowledgements This work was supported by CREST (Core Research for Evolutional Science and Technology) of JST (Japan Science and Technology Corporation). One of the authors (R.Z.) is very grateful for really very kind and warm hospitality during his stay at the Research Center for Materials Science at Extreme Conditions, Osaka University.
References [1] P. Chaudouet, Thesis, Grenoble, 1983. [2] B. Chenevier, D. Fruchart, M. Bacmann, J.P. Senateur, P. Chaudouet, L. Lundgren, Phys. Stat. Sol. A 84 (1984) 199. [3] J. BartolomeH , J. GarcmH a, L.M. FlormH a, F. Falo, R. Navarro, D. Fruchart, M. Bacmann, L.J. de Jongh, J. Magn. Magn. Mater. 54}57 (1986) 1547.
[4] C. Rillo, J. BartolomeH , M. Bacmann, B. Chenevier, D. Fruchart, R. Fruchart, J. Magn. Magn. Mater. 104}107 (1992) 1995. [5] B. Chenevier, J. Baruchel, M. Bacmann, D. Fruchart, R. Fruchart, J. Alloys Compounds 179 (1992) 147. [6] T. Kanomata, T. Kawashima, H. Utsugi, T. Goto, J. Appl. Phys. 69 (1991) 4639. [7] H. Kadomatsu, M. Isoda, K. Tohma, H. Fujii, T. Okamoto, H. Fujiwara, J. Phys. Soc. Japan 54 (1985) 269. [8] T. Eto, M. Yamagishi, M. Ishizuka, S. Endo, T. Ashida, T. Kanomata, T. Kikegawa, R. Zach, J. Alloys Compounds 307 (2000) 96. [9] T. Kanomata, K. Shirakawa, H. Yasui, T. Kaneko, J. Magn. Magn. Mater. 68 (1987) 286. [10] S. Endo, T. Sawada, T. Tsukawake, Y. Kobayashi, M. Ishizuka, K. Deguchi, M. Tokunaga, Solid State Commun. 112 (1999) 655. [11] T. Kanomata, T. Kawashima, H. Yoshida, T. Kaneko, AIP Conf. Proc. (USA) 309 (2) (1994) 1469. [12] R. Zach, R. Fruchart, D. Fruchart, S. Kaprzyk, S. Nizio", J. Magn. Magn. Mater. 104}107 (1992) 1929. [13] R. Zach, M. Bacmann, D. Fruchart, P. Wolfers, R. Fruchart, M. Guillot, S. Kaprzyk, S. Nizio, J. Tobola, J. Alloys Compounds 262}263 (1997) 508. [14] R. Zach, Zeszyty Naukowe, Politechnika Krakowska, 21 (2), 1997, p. 81 (in English).
Pressure-induced magnetic transition in MnRhAs N. Fujii *, R. Zach , M. Ishizuka , F. Ono, T. Kanomata, S. Endo Research Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka, 560-8531, Japan Department of Physics, Okayama University, Tsushima-naka, Okayama, 700-8530, Japan Department of Applied Physics, Tohoku Gakuin University, Tagajo, Miyagi, 985-8537, Japan Received 19 September 2000; received in revised form 16 November 2000
Abstract The magnetic properties of a Fe P-type intermetallic compound MnRhAs have been investigated under high pressure up to 8.0 GPa by AC susceptibility measurement. Initially, both the antiferromagnetic (AF(I)) to the canted state magnetic transition temperature ¹ and the canted state to another antiferromagnetic one (AF(II)) transition temper ature ¹ increase with compression. At 4.0 GPa, however, ¹ decreases abruptly, while the increasing rate of ¹ becomes ! ! larger above this pressure. A pressure-induced magnetic phase transition was seen at around this pressure when ¹ and ¹ are plotted in the pressure}temperature phase diagram. The transition from the antiferromagnetic to the ferromag! netic state observed below 160 K with increasing pressure is not frequently observed. 2001 Published by Elsevier Science B.V. PACS: 75.40.Cx; 72.80.Ga; 75.30. Kz; 62.50.#p Keywords: Transition metal compounds; Magnetic properties; Pressure e!ects; Magnetic phase transition; AC susceptibility
1. Introduction The ternary intermetallic compound MnRhAs crystallizes into Fe P-type (hexagonal, P6 2 m) structure with the lattice constants a"6.492 As and c"3.715 As [1]. Mn atoms locate on the pyramidal (3 g) site and Rh atoms on the tetrahedral (3f ) site. In this crystal, Mn and Rh atoms form a layer structure, each Mn layer being separated by a Rh#As atom layer along the c-axis. Therefore, * Corresponding author. Tel.: #81-6-6850-6681; fax: #816-6850-6662. E-mail address: [email protected] (N. Fujii). On leave from Institute of Physics, Technical University of Cracow, 30 084 Krakow, Poland.
MnRhAs is considered to be magnetically nearly two-dimensional. Many studies have been made for this compound because of the wide variety of its interesting magnetic phases depending upon temperature [2}4]. Fig. 1 shows an AC susceptibility vs. temperature curve observed at ambient pressure. The directions of Mn magnetic moments determined by neutron di!raction are also shown in Fig. 1 [5]. The magnetic state below ¹ "160 K is antiferromagnetic AF(I). The coexistence state of the ferromagnetic (F) and the antiferromagnetic components (canted state) appears in the temperature range between ¹ and ¹ "200 K. Another ! antiferromagnetic state which has a di!erent spin structure from AF(I) takes place above ¹ and its ! NeH el temperature is observed at ¹ "240 K [3].
0304-8853/01/$ - see front matter 2001 Published by Elsevier Science B.V. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 1 3 6 1 - 5
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
13
to 1.5 Gpa [9]. According to them, both ¹ and ¹ increased with pressure and the increasing rate ! of ¹ was larger than that of ¹ . The extrapolation ! of these curves suggested that ¹ and ¹ would ! cross at the point, ¹"240 K and p"2.45 GPa. Above this pressure, the system is expected to be AF(I) or AF(II). The purpose of the present paper is the extension of the pressure dependence of the phase transition temperatures and the investigation of the magnetic structure in the higher-pressure range up to 8 GPa.
2. Experimental procedure
Fig. 1. The upper is temperature dependence of the AC susceptibility of MnRhAs at ambient pressure. The arrows show the directions of the magnetic moment of the Mn layers [5].
MnRhP, having the same crystal structure of Fe P type is ferromagnet with ¹ "401 K and ! with the lattice constants, a"6.226 As and c"3.581 As at ambient conditions [6], both of which are smaller than in MnRhAs. Hence, the magnetic structure of these compounds is considered to be strongly dependent on the lattice constants. The original compound Fe P is well known to have a magnetic phase transition under high pressure [7]. If the lattice constants of MnRhAs were compressed to the values of MnRhP, a transformation state to a ferromagnetic one would be expected. X-ray di!raction measurements for these compounds under high pressure were made by Eto et al. [8]. According to their results, the volume of MnRhAs becomes equal to that of MnRhP at around 20 GPa. They found a structural phase transition from hexagonal to orthorhombic at around 26 GPa. The e!ect of pressure on the magnetic transition temperatures of MnRhAs was investigated by Kanomata et al. up
Polycrystalline samples of MnRhAs were prepared using ceramic method. Original elements were mixed in the desired proportion, sealed in an evacuated silica tube and annealed at about 8503C for 3 days. The sealing and annealing were repeated several times until a good-quality sample was obtained. For each time the crystal structure was investigated by using X-ray powder di!raction technique to ensure the single phase of the Fe P type. High pressure up to 8 GPa was generated by using a multianvil apparatus [10]. The front face of the anvils was a square with 4 mm edge length. To pick up the signal of AC susceptibility, the primary and the secondary coils were wound around the sample with 40 lm wire of Cu coated by polymer insulator. The sample with the pick-up coil system was put into a Te#on capsule together with the pressure medium of Florinate (3 M, FC-77). Finally, the capsule was put in the center of a cubic pressure cell made of pyrophillite. This cubic cell was compressed by six anvils. Before the experiments, the calibration of pressure was made by establishing the relation between the press load and the actual pressure based on the superconducting transition temperature of Pb. A silicon diode was attached to an anvil to detect the temperature. The temperature of the cell was controlled in the temperature range from 4.2 and 380 K using the heater wound around the anvils inside a large cryostat. The highest temperature was limited to 380 K due to the "berglassreinforced plastics adopted for the compression part of this apparatus. The AC magnetic "eld was generated by the primary coil and the signal of AC
14
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
Fig. 2. The AC susceptibility vs. temperature at various pressures up to 8.0 GPa. The ¹ and the ¹ were de"ned as the ! intersects of the baseline and the extrapolations of the peaks.
susceptibility induced in the secondary coil was detected using a lock-in ampli"er. The frequency and the maximum magnitude of the AC magnetic "eld were 990 Hz and 0.5 Oe, respectively.
3. Results and discussion The temperature dependence of the real part of the AC susceptibility s under various pressures up to 8.0 GPa is shown in Fig. 2. The imaginary part was not detected clearly due to the insu$cient S/N ratio. The two magnetic phase transition temperatures ¹ and ¹ were de"ned by Kanomata et al. ! [9] as the intersections of the baseline and the extrapolations of the maximum slopes of the peak at both sides. In this paper we followed this de"nition as shown in Fig. 2. The determination of ¹ became di$cult at pressures higher than ! 7.0 GPa due to the limitation of the measuring temperature range. It was also di$cult to deter-
mine the NeH el temperature ¹ due to its very weak signal in the AF(II) state. Both ¹ and ¹ shifted to higher temperatures ! with increasing pressure up to 4.0 GPa, at which ¹ decreased abruptly and vanished just above 5 GPa. On the other hand, T continued to increase ! with a larger rate. Thus, there is a boundary point at around 4.0 GPa, at which the slope of dT /dp changed ! abruptly and above which the shape of the AC susceptibility vs. temperature curve became ferromagnetic like. The pressure derivative d¹ /dp for ! the lower pressure range up to 4 GPa is 7.7 K/GPa, which is in good agreement with that by Kanomata et al. up to 1.5 Gpa [9]. The pressure derivative of ¹ in the higher pressure range above 4 GPa was ! d¹ /dp"30 K/GPa, which is very large compared ! with any other data previously reported [11] for Fe P-type compounds. The origin of the large pressure derivative of ¹ is probably ascribed to ! the RKKY-type exchange interaction between Mn}Mn atoms along c-axis via a Rh#As layer, which is sensitive to the Mn}Mn distance. Judging from this fact and considering the shape of the s }¹ curves above 5.0 GPa in Fig. 2, it can be concluded that a phase transformation takes place from the complex magnetic state to asimple ferromagnetic one. If the ¹ coalesces with ¹ at around 4}5 GPa, it ! should be considered that there are two kinds of ¹ , below and above this pressure. In the lower ! pressure region, ¹ is de"ned as the transition ! temperature from the canted state to the antiferromagnetic one, and in the higher-pressure region, ¹ is the usual Curie temperature from the fer! romagnetic state to the paramagnetic one. Fig. 3 shows the s }¹ curves in expanded scales under the pressures (a) up to 3.0 GPa and (b) between 3.0 and 4.5 GPa. The "ne steps of pressure were taken in the range 2.0}3.0 GPa so as to observe how ¹ and ¹ became close to each other at ! around 2.5 GPa. The temperature width of the region for the canted state became narrower as the pressure increased up to 3.0 GPa and the peak of AC susceptibility value became weaker. Above 4 GPa the temperature width spread rapidly, and the peak value increased gradually. The p}T phase diagram for MnRhAs determined from the result of the present experiments is shown
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
Fig. 3. The s }¹ curves in expanded scales under the pressures: (a) 1.0, 2.0, 2.3, 2.6 and 3.0 GPa; (b) 3.0, 3.5, 4.0 and 4.5 GPa. Both of the width of the peak and the heights of the intensity decrease up to 3.0 GPa, and then, the width increase rapidly above 4 GPa.
in Fig. 4. There should be a border between the canted state and the ferromagnetic one as shown by the dotted line which was just an extension of the line originally drawn by Kanomata et al. [9]. This magnetic phase diagram is very similar to that of MnRhAs P system at ambient pressure [1,12], \V V when the fraction x is converted to pressure. Similar behavior was also found under pressure in the case of the MnRhAs P series of compounds. \V V Firstly, for the content x"0.4, where the ¹ vari ation vs. external pressure p and vs. chemical substitution x present the same non-linear character [12,14]. Secondly, for the content x"0.5 the pressure-induced ferromagnetic state was experimentally obtained. Those results were con"rmed both by the AC susceptibility and the magnetization measurements carried out under pressure up to 1.5 GPa [12}14]. To determine the magnetic
15
Fig. 4. The p}¹ phase diagram determined from the present experiment. A pressure-induced phase transition from the AF(I) to the F takes place at around 5.0 GPa. ¹ was not detected in this experiment. The dotted line between ¹ and ¹ was drawn ! along extension of Kanomata et al. [9].
phases diagrams more precisely, magnetization measurements in high magnetic "elds and neutron di!raction experiments under high pressure up to at least 6 GPa are necessary.
4. Conclusion By AC susceptibility measurements in MnRhAs under high pressures, it was found that both the magnetic phase transition temperature from antiferromagnetic state (AF(I)) to canted one, ¹ , and from canted state to antiferromagnetic one (AF(II)), ¹ , increased gradually with pressure up to ! 4.0 GPa. Then ¹ decreased suddenly and vanished just above 5 GPa. Above this pressure the system became purely ferromagnetic. This is a new pressure-induced magnetic phase transition from antiferromagnetic to ferromagnetic state. At this phase transition, the pressure derivative of ¹ in! creased suddenly from 7.7 to 30 K/GPa. This value
16
N. Fujii et al. / Journal of Magnetism and Magnetic Materials 224 (2001) 12}16
is very large compared with the data reported so far for Fe P-type compounds. Acknowledgements This work was supported by CREST (Core Research for Evolutional Science and Technology) of JST (Japan Science and Technology Corporation). One of the authors (R.Z.) is very grateful for really very kind and warm hospitality during his stay at the Research Center for Materials Science at Extreme Conditions, Osaka University.
References [1] P. Chaudouet, Thesis, Grenoble, 1983. [2] B. Chenevier, D. Fruchart, M. Bacmann, J.P. Senateur, P. Chaudouet, L. Lundgren, Phys. Stat. Sol. A 84 (1984) 199. [3] J. BartolomeH , J. GarcmH a, L.M. FlormH a, F. Falo, R. Navarro, D. Fruchart, M. Bacmann, L.J. de Jongh, J. Magn. Magn. Mater. 54}57 (1986) 1547.
[4] C. Rillo, J. BartolomeH , M. Bacmann, B. Chenevier, D. Fruchart, R. Fruchart, J. Magn. Magn. Mater. 104}107 (1992) 1995. [5] B. Chenevier, J. Baruchel, M. Bacmann, D. Fruchart, R. Fruchart, J. Alloys Compounds 179 (1992) 147. [6] T. Kanomata, T. Kawashima, H. Utsugi, T. Goto, J. Appl. Phys. 69 (1991) 4639. [7] H. Kadomatsu, M. Isoda, K. Tohma, H. Fujii, T. Okamoto, H. Fujiwara, J. Phys. Soc. Japan 54 (1985) 269. [8] T. Eto, M. Yamagishi, M. Ishizuka, S. Endo, T. Ashida, T. Kanomata, T. Kikegawa, R. Zach, J. Alloys Compounds 307 (2000) 96. [9] T. Kanomata, K. Shirakawa, H. Yasui, T. Kaneko, J. Magn. Magn. Mater. 68 (1987) 286. [10] S. Endo, T. Sawada, T. Tsukawake, Y. Kobayashi, M. Ishizuka, K. Deguchi, M. Tokunaga, Solid State Commun. 112 (1999) 655. [11] T. Kanomata, T. Kawashima, H. Yoshida, T. Kaneko, AIP Conf. Proc. (USA) 309 (2) (1994) 1469. [12] R. Zach, R. Fruchart, D. Fruchart, S. Kaprzyk, S. Nizio", J. Magn. Magn. Mater. 104}107 (1992) 1929. [13] R. Zach, M. Bacmann, D. Fruchart, P. Wolfers, R. Fruchart, M. Guillot, S. Kaprzyk, S. Nizio, J. Tobola, J. Alloys Compounds 262}263 (1997) 508. [14] R. Zach, Zeszyty Naukowe, Politechnika Krakowska, 21 (2), 1997, p. 81 (in English).