In order to microscopically investigate the properties in SrGa 4 , the Ga NMR measurements of a p... more In order to microscopically investigate the properties in SrGa 4 , the Ga NMR measurements of a powder sample were carried out. The Ga NMR spectra corresponding to Ga(I) and Ga(II) sites are obtained. The NMR spectra of 69&71 Ga (a nuclear spinI = 3/2) in the powder sample of SrGa 4 do not take a typical powder pattern caused by the NQR interaction, but take the spectra consisting of three well resolved resonance-lines, which indicates that the nonuniform distribution of crystal orientation in the powder sample occurs because of the magnetic anisotropy. From the analysis of the Ga NMR spectrum, it is found that the ab-plane of the crystal is parallel to the external magnetic field, which would be attributed to the anisotropy of the magnetic susceptibility with the easy axis parallel to the ab-plane. This result is also confirmed by the 69 Ga NQR in SrGa 4. The Knight shifts of the 69 Ga(I) and 69 Ga(II) shift slightly to the negative side with decreasing temperature due to the core polarization of the d-electrons. The values of the Knight shift of the 69 Ga(I) and 69 Ga(II) are 0.01 and-0.11 % at 4.2 K, and 0.09 and-0.08 % at 300 K, respectively. The values of the 1/T 1 T of the NMR of both 69 Ga(I) and 69 Ga(II) are almost constant between 4.2 and 100 K, whose values are 1.5 s −1 K −1 at 69 Ga(I) and 0.12 s −1 K −1 at 69 Ga(II), while the 1/T 1 T slightly increases above 100 K with increasing temperature. The value of T 1 of 69 Ga(I) is one order of magnitude less than that of 69 Ga(II).
Co and 31 P nuclear magnetic resonance (NMR) measurements in external magnetic and zero magnetic ... more Co and 31 P nuclear magnetic resonance (NMR) measurements in external magnetic and zero magnetic fields have been performed to investigate the magnetic properties of the A-type antiferromagnetic (AFM) CaCo2P2. NMR data, especially, the nuclear spin lattice relaxation rates 1/T1 exhibiting a clear peak, provide clear evidence for the AFM transition at a Néel temperature of TN ∼110 K. The magnetic fluctuations in the paramagnetic state were found to be three-dimensional ferromagnetic, suggesting ferromagnetic interaction between Co spins in the ab plane characterize the spin correlations in the paramagnetic state. In the AFM state below TN, we have observed 59 Co and 31 P NMR signals under zero magnetic field. From 59 Co NMR data, the ordered magnetic moments of Co are found to be in ab plane and are estimated to be 0.35 µB at 4.2 K. Furthermore, the external field dependence of 59 Co NMR spectrum in the AFM state suggests a very weak magnetic anisotropy of the Co ions and also provides microscopic evidence of canting the Co ordered moments along the external magnetic field directions. The magnetic state of the Co ions in CaCo2P2 is well explained by the local moment picture in the AFM state, although the system is metallic as seen by 1/T1T = constant behavior.
Journal of Evidence Based Medicine and Healthcare, 2016
BACKGROUND In view of the increase in the incidence of falciparum malaria in our area, most of th... more BACKGROUND In view of the increase in the incidence of falciparum malaria in our area, most of the patients coming from malaria endemic areas, to know the spectrum of malaria in a district level teaching hospital, we have taken up this subject. METHODS It was a Prospective Observational Study during the years July 2013 to July 2015. All children with clinical suspicion of malaria between age group of 0-12 years were admitted in paediatric ward. RESULTS During the period of study in 2 years, we have observed that there is progressive increase in the incidence of pf. malaria with particular increase during the months of July to October which is being a rainy season. Retrospective data of the number of pf. malaria cases admitted in our hospital in the previous two years also showed increased incidence. CONCLUSIONS Supportive treatment like control of fever, convulsions, blood transfusion is as equally important as specific treatment. Parasite F test is easy to diagnose, even a health worker in PHC can diagnose. Outcome is good when the treatment is started early pointing out to the importance of quick diagnosis and treatment.
We performed an 75 As nuclear quadrupole resonance (NQR) measurement on CeOs4As12. The 75 As-NQR ... more We performed an 75 As nuclear quadrupole resonance (NQR) measurement on CeOs4As12. The 75 As-NQR spectrum shape demonstrates that the Ce-site filling fraction of our high-pressure synthesized sample is close to unity. A presence of the c − f hybridization gap is confirmed from the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1. An increase of 1/T1 below ∼3 K indicates a development of the spin fluctuations. The 1/T1 for CeOs4As12 shows similar behavior as that for CeOs4Sb12 with different magnitude of the c − f hybridization gap. An absence of phase transition in CeOs4As12 may be caused by the increase of the c − f hybridization, which increases the gap magnitude and reduces the residual density of state inside the gap.
In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Néel temperature. ... more In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Néel temperature. The magnetic structure below was reported to be helical with the helix axis along the c-axis from the neutron diffraction study. We report the results of 153Eu, 59Co and 31P nuclear magnetic resonance (NMR) measurements on EuCo2P2 using a single crystal and a powdered sample. In the antiferromagnetic (AFM) state, we succeeded in observing 153Eu, 59Co and 31P NMR spectra in zero magnetic field. The sharp 153Eu zero field NMR (ZF NMR) lines indicate homogeneous Eu ordered moment. The 59Co and 31P ZF NMR spectra showed an asymmetric spectral shape, indicating a distribution of the internal magnetic induction at each nuclear position. The AFM propagation vector k characterizing the helical AFM state can be determined from the internal magnetic induction at Co site. We have determined the model-independent value of the AFM propagation vector k distributed from (0, 0, 0.86)2π
Ternary CePt3Si crystallizes in the tetragonal P4mm structure which lacks a center of inversion. ... more Ternary CePt3Si crystallizes in the tetragonal P4mm structure which lacks a center of inversion. Antiferromagnetic order sets in at TN ~ 2.2 K followed by superconductivity (SC) below Tc ~ 0.75 K. Large values of H'c2 ~ -8.5 T/K and Hc2(0) ~ 4 to 5 T were derived, referring to Cooper pairs formed out of heavy quasiparticles. The mass enhancement
ABSTRACT EuAl4 orders antiferromagnetically at TN ≈ 16 K with an effective magnetic moment of 8.0... more ABSTRACT EuAl4 orders antiferromagnetically at TN ≈ 16 K with an effective magnetic moment of 8.02 μB. In the paramagnetic phase, the magnetic susceptibility of EuAl4 follows the Curie-Weiss law with a positive Curie-Weiss temperature θP = +14 K. The antiferromagnetic state is changed into the field induced ferromagnetic state at a critical field Hc of approximately 2 T. In order to microscopically investigate the magnetic and electronic properties in EuAl4, the NMR measurements of EuAl4 have been carried out at temperatures between 2 and 300 K, applying an external magnetic field of approximately 6.5 T. The 27Al NMR spectra corresponding to Al(I) and Al(II) sites are obtained. From the 27Al NMR spectra, the isotropic part Kiso and anisotropic part Kaniso of Knight shift, and nuclear quadrupole frequncy νQ are obtained. The Kiso and Kaniso shift to negative side with decreasing temperature due to the RKKY interaction. These temperature dependences follow the Curie-Weiss law with θP = +14 K, which is consistent with that of the magnetic susceptibility. From the K - χ plot, the values of the hyperfine fields Hhf_iso and Hhf_aniso are -3.231 and -0.162 kOe/μB for Al(I) site, and -1.823 and -0.264 kOe/μB for Al(II) site, respectively. The values of νQ of 27Al nucleus for Al(I) and Al(II) sites are approximately 0.865 and 0.409 MHz, respectively. The nuclear relaxation time T1 of 27Al NMR for both sites is almost constant in the paramagnetic phase, while the value of 1/T1 is abruptly decreased in the ordered ferromagnetic state.
The electrical resistivity ρ and the thermopower S of the single crystalline sample of the Heusle... more The electrical resistivity ρ and the thermopower S of the single crystalline sample of the Heusler compound Mn3Si have been measured in the temperature range between 2 and 300 K under high pressures up to 2.2 GPa. The temperature variations of ρ and S indicate the characteristic features at the Neel temperature TN. An additional anomaly in S(T), related to the 3Q satellites in SDW, is observed at P > 1 GPa, and it disappears at P > 1 GPa. The Neel temperature, obtained from ρ(T) and S(T) curves, increases with increasing pressure. The pressure dependences of the residual resistivity and the thermopower at T = 2 K show the discontinuous changes at P ≈ 1 GPa, indicating a pressure induced phase transition.
We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional super... more We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional superconducting (SC) property in the filled-skutterudite compound PrOs4Sb12 revealing a SC transition temperature Tc = 1.85 K. The temperature (T) dependence of nuclear-spin-lattice-relaxation rate 1/T1 and NQR frequency unravel a low-lying crystal-electric-field splitting below T0 ∼ 10 K, associated with Pr 3+ (4f 2)-derived ground state. The emergence of T1T =const. behavior below TF ∼ 4 K points to the formation of heavy-quasiparticle state. In the SC state, 1/T1 shows neither a coherence peak nor a T 3 like power-law behavior observed for HF superconductors to date. The isotropic energy-gap with a size of gap ∆/kB = 4.8 K begins to already open up at T * ∼ 2.3 K without any coherence effect just below Tc = 1.85 K. We highlight that the superconductivity in PrOs4Sb12, which is in an unconventional strong-coupling regime, differs from a conventional s-wave type and any unconventional ones with the line-node gap.
We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmet... more We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmetric CePt3Si through measurements of the 195 Pt nuclear spin-lattice relaxation rate 1/T1. In the normal state, the temperature (T) dependence of 1/T1 unraveled the existence of low-lying levels in crystal-electric-field multiplets and the formation of a heavy fermion (HF) state. The coexistence of AFM and SC phases, that emerge at TN = 2.2 K and Tc = 0.75 K, respectively, takes place on a microscopic level. CePt3Si is the first HF superconductor that reveals a peak in 1/T1 just below Tc and, additionally, does not follow the T 3 law that used to be reported for most unconventional HF superconductors. We remark that this unexpected SC characteristics may be related with the lack of an inversion center in its crystal structure.
31 P-NMR studies have been carried out to investigate magnetic properties in the Pr-based filled ... more 31 P-NMR studies have been carried out to investigate magnetic properties in the Pr-based filled skutterudite compound PrFe 4 P 12. This compound shows an unusual phase transition at T A ϳ 6.5 K, which is now regarded as antiferroquadrupole ͑AFQ͒ ordering from neutron-diffraction experiments. Splitting of the P-NMR spectrum due to the appearance of two P sites with different hyperfine fields was observed below T A. From the field dependence, the splitting seems to disappear in zero magnetic field, indicating that the different hyperfine fields are not due to magnetic order, but to the appearance of two inequivalent P sites below T A. This is ascribed to the distortion of the P cage surrounding a Pr ion below T A , which is associated with the Pr orbital ordering. The nuclear spin-lattice relaxation rate ͑1/T 1 ͒ shows the typical behavior of Kondo systems, where onset of local-moment screening due to the coupling between conduction and localized Pr-4f electrons is observed below 50 K. Far above a critical field H A ϳ 50 kOe, the Korringa behavior T 1 T = const is observed below 2 K in 100 kOe. The Korringa value below 2 K is one order of magnitude larger than that in LaFe 4 P 12 , which has no 4f electrons. Our NMR experiment shows that the heavy-fermion state is realized far above H A in PrFe 4 P 12. The magnetic fluctuations in PrFe 4 P 12 are discussed from a comparison with typical heavy-fermion compounds. In magnetic fields below H A , 1/T 1 shows a sharp decrease below T A , however, in smaller magnetic fields less than 10 kOe, 1 / T 1 stays constant far below T A with a relatively large value. The temperature and field dependence of 1 / T 1 reveals the presence of low-energy spin fluctuations in the low-temperature and low-field region. These unusual magnetic fluctuations are considered to originate from the magnetic dynamics of Pr-nuclear spins since the fluctuating magnetic field ϳ1.4 Oe and frequency ϳ3.5 MHz are so small. The nuclear ordering temperature is estimated to be ϳ0.08 mK using the nuclear exchange fluctuations derived from the observed 1 / T 1 of P. We show that PrFe 4 P 12 is a quite unique compound in which nuclear magnetism can be detected by P NMR thanks to the nonmagnetic ground state of the Pr-4f moments.
We report a Knight-shift (29 K) study of 29 Si of the noncentrosymmetric heavy-fermion supercondu... more We report a Knight-shift (29 K) study of 29 Si of the noncentrosymmetric heavy-fermion superconductor CePt 3 Si. The spin part of 29 K is deduced to be K s ¼ 0:13-0.18% and 0.19-0.22% at respective fields of H ¼ 2:0061 and 0.8671 T. The 29 K c for the field direction Hkcaxis unchanges across T c , suggesting that a two-component order parameter composed of spin-singlet and spin-triplet pairing components is realized.
We report on a 195Pt-NMR study of the antiferromagnetic heavy-fermion (HF) superconductor CePt3Si... more We report on a 195Pt-NMR study of the antiferromagnetic heavy-fermion (HF) superconductor CePt3Si without an inversion center. The measurements of the nuclear spin-lattice relaxation rate 1/T1 has revealed a uniform coexistence of antiferromagnetism and superconductivity. CePt3Si is the first HF superconductor that reveals a peak in 1/T1 just below Tc and, additionally, does not follow the T3 law that was
We report the measurements of the 29 Si Knight shift 29 K on the noncentrosymmetric heavyfermion ... more We report the measurements of the 29 Si Knight shift 29 K on the noncentrosymmetric heavyfermion compound CePt3Si in which antiferromagnetism (AFM) with TN = 2.2 K coexists with superconductivity (SC) with Tc = 0.75 K. Its spin part 29 Ks, which is deduced to be K c s ≥ 0.11 and 0.16% at respective magnetic fields H = 2.0061 and 0.8671 T, does not decrease across the superconducting transition temperature Tc for the field along the c-axis. The temperature dependence of nuclear spin-lattice relaxation of 195 Pt below Tc has been accounted for by a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components. From this result, it is shown that the Knight-shift data are consistent with the occurrence of the two-component order parameter for CePt3Si.
In order to microscopically investigate the properties in SrGa 4 , the Ga NMR measurements of a p... more In order to microscopically investigate the properties in SrGa 4 , the Ga NMR measurements of a powder sample were carried out. The Ga NMR spectra corresponding to Ga(I) and Ga(II) sites are obtained. The NMR spectra of 69&71 Ga (a nuclear spinI = 3/2) in the powder sample of SrGa 4 do not take a typical powder pattern caused by the NQR interaction, but take the spectra consisting of three well resolved resonance-lines, which indicates that the nonuniform distribution of crystal orientation in the powder sample occurs because of the magnetic anisotropy. From the analysis of the Ga NMR spectrum, it is found that the ab-plane of the crystal is parallel to the external magnetic field, which would be attributed to the anisotropy of the magnetic susceptibility with the easy axis parallel to the ab-plane. This result is also confirmed by the 69 Ga NQR in SrGa 4. The Knight shifts of the 69 Ga(I) and 69 Ga(II) shift slightly to the negative side with decreasing temperature due to the core polarization of the d-electrons. The values of the Knight shift of the 69 Ga(I) and 69 Ga(II) are 0.01 and-0.11 % at 4.2 K, and 0.09 and-0.08 % at 300 K, respectively. The values of the 1/T 1 T of the NMR of both 69 Ga(I) and 69 Ga(II) are almost constant between 4.2 and 100 K, whose values are 1.5 s −1 K −1 at 69 Ga(I) and 0.12 s −1 K −1 at 69 Ga(II), while the 1/T 1 T slightly increases above 100 K with increasing temperature. The value of T 1 of 69 Ga(I) is one order of magnitude less than that of 69 Ga(II).
Co and 31 P nuclear magnetic resonance (NMR) measurements in external magnetic and zero magnetic ... more Co and 31 P nuclear magnetic resonance (NMR) measurements in external magnetic and zero magnetic fields have been performed to investigate the magnetic properties of the A-type antiferromagnetic (AFM) CaCo2P2. NMR data, especially, the nuclear spin lattice relaxation rates 1/T1 exhibiting a clear peak, provide clear evidence for the AFM transition at a Néel temperature of TN ∼110 K. The magnetic fluctuations in the paramagnetic state were found to be three-dimensional ferromagnetic, suggesting ferromagnetic interaction between Co spins in the ab plane characterize the spin correlations in the paramagnetic state. In the AFM state below TN, we have observed 59 Co and 31 P NMR signals under zero magnetic field. From 59 Co NMR data, the ordered magnetic moments of Co are found to be in ab plane and are estimated to be 0.35 µB at 4.2 K. Furthermore, the external field dependence of 59 Co NMR spectrum in the AFM state suggests a very weak magnetic anisotropy of the Co ions and also provides microscopic evidence of canting the Co ordered moments along the external magnetic field directions. The magnetic state of the Co ions in CaCo2P2 is well explained by the local moment picture in the AFM state, although the system is metallic as seen by 1/T1T = constant behavior.
Journal of Evidence Based Medicine and Healthcare, 2016
BACKGROUND In view of the increase in the incidence of falciparum malaria in our area, most of th... more BACKGROUND In view of the increase in the incidence of falciparum malaria in our area, most of the patients coming from malaria endemic areas, to know the spectrum of malaria in a district level teaching hospital, we have taken up this subject. METHODS It was a Prospective Observational Study during the years July 2013 to July 2015. All children with clinical suspicion of malaria between age group of 0-12 years were admitted in paediatric ward. RESULTS During the period of study in 2 years, we have observed that there is progressive increase in the incidence of pf. malaria with particular increase during the months of July to October which is being a rainy season. Retrospective data of the number of pf. malaria cases admitted in our hospital in the previous two years also showed increased incidence. CONCLUSIONS Supportive treatment like control of fever, convulsions, blood transfusion is as equally important as specific treatment. Parasite F test is easy to diagnose, even a health worker in PHC can diagnose. Outcome is good when the treatment is started early pointing out to the importance of quick diagnosis and treatment.
We performed an 75 As nuclear quadrupole resonance (NQR) measurement on CeOs4As12. The 75 As-NQR ... more We performed an 75 As nuclear quadrupole resonance (NQR) measurement on CeOs4As12. The 75 As-NQR spectrum shape demonstrates that the Ce-site filling fraction of our high-pressure synthesized sample is close to unity. A presence of the c − f hybridization gap is confirmed from the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1. An increase of 1/T1 below ∼3 K indicates a development of the spin fluctuations. The 1/T1 for CeOs4As12 shows similar behavior as that for CeOs4Sb12 with different magnitude of the c − f hybridization gap. An absence of phase transition in CeOs4As12 may be caused by the increase of the c − f hybridization, which increases the gap magnitude and reduces the residual density of state inside the gap.
In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Néel temperature. ... more In EuCo2P2, 4f electron spins of Eu2+ ions order antiferromagnetically below a Néel temperature. The magnetic structure below was reported to be helical with the helix axis along the c-axis from the neutron diffraction study. We report the results of 153Eu, 59Co and 31P nuclear magnetic resonance (NMR) measurements on EuCo2P2 using a single crystal and a powdered sample. In the antiferromagnetic (AFM) state, we succeeded in observing 153Eu, 59Co and 31P NMR spectra in zero magnetic field. The sharp 153Eu zero field NMR (ZF NMR) lines indicate homogeneous Eu ordered moment. The 59Co and 31P ZF NMR spectra showed an asymmetric spectral shape, indicating a distribution of the internal magnetic induction at each nuclear position. The AFM propagation vector k characterizing the helical AFM state can be determined from the internal magnetic induction at Co site. We have determined the model-independent value of the AFM propagation vector k distributed from (0, 0, 0.86)2π
Ternary CePt3Si crystallizes in the tetragonal P4mm structure which lacks a center of inversion. ... more Ternary CePt3Si crystallizes in the tetragonal P4mm structure which lacks a center of inversion. Antiferromagnetic order sets in at TN ~ 2.2 K followed by superconductivity (SC) below Tc ~ 0.75 K. Large values of H'c2 ~ -8.5 T/K and Hc2(0) ~ 4 to 5 T were derived, referring to Cooper pairs formed out of heavy quasiparticles. The mass enhancement
ABSTRACT EuAl4 orders antiferromagnetically at TN ≈ 16 K with an effective magnetic moment of 8.0... more ABSTRACT EuAl4 orders antiferromagnetically at TN ≈ 16 K with an effective magnetic moment of 8.02 μB. In the paramagnetic phase, the magnetic susceptibility of EuAl4 follows the Curie-Weiss law with a positive Curie-Weiss temperature θP = +14 K. The antiferromagnetic state is changed into the field induced ferromagnetic state at a critical field Hc of approximately 2 T. In order to microscopically investigate the magnetic and electronic properties in EuAl4, the NMR measurements of EuAl4 have been carried out at temperatures between 2 and 300 K, applying an external magnetic field of approximately 6.5 T. The 27Al NMR spectra corresponding to Al(I) and Al(II) sites are obtained. From the 27Al NMR spectra, the isotropic part Kiso and anisotropic part Kaniso of Knight shift, and nuclear quadrupole frequncy νQ are obtained. The Kiso and Kaniso shift to negative side with decreasing temperature due to the RKKY interaction. These temperature dependences follow the Curie-Weiss law with θP = +14 K, which is consistent with that of the magnetic susceptibility. From the K - χ plot, the values of the hyperfine fields Hhf_iso and Hhf_aniso are -3.231 and -0.162 kOe/μB for Al(I) site, and -1.823 and -0.264 kOe/μB for Al(II) site, respectively. The values of νQ of 27Al nucleus for Al(I) and Al(II) sites are approximately 0.865 and 0.409 MHz, respectively. The nuclear relaxation time T1 of 27Al NMR for both sites is almost constant in the paramagnetic phase, while the value of 1/T1 is abruptly decreased in the ordered ferromagnetic state.
The electrical resistivity ρ and the thermopower S of the single crystalline sample of the Heusle... more The electrical resistivity ρ and the thermopower S of the single crystalline sample of the Heusler compound Mn3Si have been measured in the temperature range between 2 and 300 K under high pressures up to 2.2 GPa. The temperature variations of ρ and S indicate the characteristic features at the Neel temperature TN. An additional anomaly in S(T), related to the 3Q satellites in SDW, is observed at P > 1 GPa, and it disappears at P > 1 GPa. The Neel temperature, obtained from ρ(T) and S(T) curves, increases with increasing pressure. The pressure dependences of the residual resistivity and the thermopower at T = 2 K show the discontinuous changes at P ≈ 1 GPa, indicating a pressure induced phase transition.
We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional super... more We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional superconducting (SC) property in the filled-skutterudite compound PrOs4Sb12 revealing a SC transition temperature Tc = 1.85 K. The temperature (T) dependence of nuclear-spin-lattice-relaxation rate 1/T1 and NQR frequency unravel a low-lying crystal-electric-field splitting below T0 ∼ 10 K, associated with Pr 3+ (4f 2)-derived ground state. The emergence of T1T =const. behavior below TF ∼ 4 K points to the formation of heavy-quasiparticle state. In the SC state, 1/T1 shows neither a coherence peak nor a T 3 like power-law behavior observed for HF superconductors to date. The isotropic energy-gap with a size of gap ∆/kB = 4.8 K begins to already open up at T * ∼ 2.3 K without any coherence effect just below Tc = 1.85 K. We highlight that the superconductivity in PrOs4Sb12, which is in an unconventional strong-coupling regime, differs from a conventional s-wave type and any unconventional ones with the line-node gap.
We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmet... more We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmetric CePt3Si through measurements of the 195 Pt nuclear spin-lattice relaxation rate 1/T1. In the normal state, the temperature (T) dependence of 1/T1 unraveled the existence of low-lying levels in crystal-electric-field multiplets and the formation of a heavy fermion (HF) state. The coexistence of AFM and SC phases, that emerge at TN = 2.2 K and Tc = 0.75 K, respectively, takes place on a microscopic level. CePt3Si is the first HF superconductor that reveals a peak in 1/T1 just below Tc and, additionally, does not follow the T 3 law that used to be reported for most unconventional HF superconductors. We remark that this unexpected SC characteristics may be related with the lack of an inversion center in its crystal structure.
31 P-NMR studies have been carried out to investigate magnetic properties in the Pr-based filled ... more 31 P-NMR studies have been carried out to investigate magnetic properties in the Pr-based filled skutterudite compound PrFe 4 P 12. This compound shows an unusual phase transition at T A ϳ 6.5 K, which is now regarded as antiferroquadrupole ͑AFQ͒ ordering from neutron-diffraction experiments. Splitting of the P-NMR spectrum due to the appearance of two P sites with different hyperfine fields was observed below T A. From the field dependence, the splitting seems to disappear in zero magnetic field, indicating that the different hyperfine fields are not due to magnetic order, but to the appearance of two inequivalent P sites below T A. This is ascribed to the distortion of the P cage surrounding a Pr ion below T A , which is associated with the Pr orbital ordering. The nuclear spin-lattice relaxation rate ͑1/T 1 ͒ shows the typical behavior of Kondo systems, where onset of local-moment screening due to the coupling between conduction and localized Pr-4f electrons is observed below 50 K. Far above a critical field H A ϳ 50 kOe, the Korringa behavior T 1 T = const is observed below 2 K in 100 kOe. The Korringa value below 2 K is one order of magnitude larger than that in LaFe 4 P 12 , which has no 4f electrons. Our NMR experiment shows that the heavy-fermion state is realized far above H A in PrFe 4 P 12. The magnetic fluctuations in PrFe 4 P 12 are discussed from a comparison with typical heavy-fermion compounds. In magnetic fields below H A , 1/T 1 shows a sharp decrease below T A , however, in smaller magnetic fields less than 10 kOe, 1 / T 1 stays constant far below T A with a relatively large value. The temperature and field dependence of 1 / T 1 reveals the presence of low-energy spin fluctuations in the low-temperature and low-field region. These unusual magnetic fluctuations are considered to originate from the magnetic dynamics of Pr-nuclear spins since the fluctuating magnetic field ϳ1.4 Oe and frequency ϳ3.5 MHz are so small. The nuclear ordering temperature is estimated to be ϳ0.08 mK using the nuclear exchange fluctuations derived from the observed 1 / T 1 of P. We show that PrFe 4 P 12 is a quite unique compound in which nuclear magnetism can be detected by P NMR thanks to the nonmagnetic ground state of the Pr-4f moments.
We report a Knight-shift (29 K) study of 29 Si of the noncentrosymmetric heavy-fermion supercondu... more We report a Knight-shift (29 K) study of 29 Si of the noncentrosymmetric heavy-fermion superconductor CePt 3 Si. The spin part of 29 K is deduced to be K s ¼ 0:13-0.18% and 0.19-0.22% at respective fields of H ¼ 2:0061 and 0.8671 T. The 29 K c for the field direction Hkcaxis unchanges across T c , suggesting that a two-component order parameter composed of spin-singlet and spin-triplet pairing components is realized.
We report on a 195Pt-NMR study of the antiferromagnetic heavy-fermion (HF) superconductor CePt3Si... more We report on a 195Pt-NMR study of the antiferromagnetic heavy-fermion (HF) superconductor CePt3Si without an inversion center. The measurements of the nuclear spin-lattice relaxation rate 1/T1 has revealed a uniform coexistence of antiferromagnetism and superconductivity. CePt3Si is the first HF superconductor that reveals a peak in 1/T1 just below Tc and, additionally, does not follow the T3 law that was
We report the measurements of the 29 Si Knight shift 29 K on the noncentrosymmetric heavyfermion ... more We report the measurements of the 29 Si Knight shift 29 K on the noncentrosymmetric heavyfermion compound CePt3Si in which antiferromagnetism (AFM) with TN = 2.2 K coexists with superconductivity (SC) with Tc = 0.75 K. Its spin part 29 Ks, which is deduced to be K c s ≥ 0.11 and 0.16% at respective magnetic fields H = 2.0061 and 0.8671 T, does not decrease across the superconducting transition temperature Tc for the field along the c-axis. The temperature dependence of nuclear spin-lattice relaxation of 195 Pt below Tc has been accounted for by a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components. From this result, it is shown that the Knight-shift data are consistent with the occurrence of the two-component order parameter for CePt3Si.
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Papers by M. Yogi