Inhomogeneous Ferromagnetism and Spin-Glass-Like Behavior in <inline-formula> <tex-math notation='TeX'> <tex> $({\rm Nd}_{1-x}{\rm Y}_{x})_{0.7}{\rm Sr}_{0.3}{\rm MnO}_{3}$ </tex> </tex-math></inline-formula> With <inline-formula> <tex-math notation='TeX

Phan, T. L.,Nguyen, V. D.,Ho, T. A.,Khiem, N. V.,Thanh, T. D.,Phuc, N. X.,Thang, P. D.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.6

<P>The magnetic properties of polycrystalline ceramic samples (Nd1-xYx)(0.7)Sr0.3MnO3 with x = 0.21 - 0.35 were studied by means of dc magnetization and ac susceptibility measurements. Experimental results reveal a strong decrease of the ferromagnetic (FM)-paramagnetic phase-transition temperature (T-C) from 97 to 65 K as increasing x from 0.21 to 0.35, respectively. There is magnetic inhomogeneity associated with short-range FM order. Particularly, the samples undergo a spin-glass (SG) phase transition at the so-called blocking temperature (T-B) below T-C, which shifts toward lower temperatures with increasing the applied field, Hex; T-B -> T-g (the SG phase-transition temperature) as H-ex -> 0. The existence of the SG behavior in these samples was also confirmed by frequency (f) dependences of the ac susceptibility. For the in-phase/real component, chi' (T), it shows a frequency-dependent peak at the SG freezing temperature (T-f); T-f -> T-g as f -> 0. Dynamics of this process were analyzed by means of the slowing down scaling law, tau/tau(0) proportional to (T-f/T-g - 1)(-zv), where tau(0) and zv are the characteristic time and critical exponent, respectively. Fitting the experimental T-f(f) data to the scaling law gave the results of zv = 10.1-12.3 and tau(0) = 10(-21)-10(-15)s. These values are different from those expected for canonical SG systems with zv = 10 and tau(0) = 10(-13)s, revealing the cluster-SG behavior of (Nd1-xYx)(0.7)Sr0.3MnO3 samples. Notably, the increase in Y content leads to the shift of tau(0) and zv values toward those of canonical SG systems, which is ascribed to an expansion of SG clusters.</P>

Magnetic and magnetocaloric properties in La_0.7Ca_0.3-xNa_xMnO₃ exhibiting first-order and second-order magnetic phase transitions

Ho, T.A.,Dang, N.T.,Phan, T.L.,Yang, D.S.,Lee, B.W.,Yu, S.C. Elsevier Sequoia 2016 JOURNAL OF ALLOYS AND COMPOUNDS Vol.676 No.-

Polycrystalline orthorhombic samples La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Na<SUB>x</SUB>MnO<SUB>3</SUB> (x = 0-0.09) were prepared by solid-state reaction. The study of magnetic properties revealed that the ferromagnetic-paramagnetic (FM-PM) transition temperature (T<SUB>C</SUB>) increases from 255 to about 271 K with increasing Na-doping content (x) from 0 to 0.09, respectively. Around the T<SUB>C</SUB>, we have found the samples showing a large magnetocaloric (MC) effect with maximum values of magnetic entropy change (|ΔS<SUB>max</SUB>|) of 7-8 J kg<SUP>-1</SUP> K<SUP>-1</SUP> and relative cooling power RCP = 232-236 J/kg for the samples x = 0.03-0.09 in a magnetic-field interval ΔH = 40 kOe. Detailed analyses of isothermal magnetization data M(T, H) based on Banerjee's criteria indicated a first-to-second-order magnetic-phase transformation taking place at a threshold Na-doping concentration x<SUB>c</SUB> ~ 0.06. This could also be observed clearly from the feature of entropy universal curves. An assessment of the magnetic-ordering exponent N = dLn|ΔS<SUB>m</SUB>|/dLnH demonstrates an existence of short-range magnetic order in the samples. We believe that the changes of the magnetic properties and MC effect in La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Na<SUB>x</SUB>MnO<SUB>3</SUB> caused by Na doping are related to the changes in the structural parameters and Mn<SUP>4+</SUP>/Mn<SUP>3+</SUP> ratio, which are confirmed by the geometrical and electronic analyses based on X-ray diffraction and X-ray absorption fine structure.

An Effective Route to Control the Magnetic-Phase Transition and Magnetocaloric Effect of La_0.7Ca_0.3MnO₃ Nanoparticles

Phan, T. L.,Thanh, T. D.,Ho, T. A.,Manh, T. V.,Tran, Q. T.,Lampen, P.,Phan, M. H.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.11

<P>This paper points out that the magnetic-phase transition and magnetocaloric effect of La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> (LCMO) can be easily controlled by using the mechanical milling method. Changing the milling time from 5 to 30 min, we have obtained LCMO nanoparticles (NPs) with average crystallite sizes (d, determined by the Williamson-Hall method) ranging from 100 to 45 nm. The magnetic studies (based on a superconducting quantum interference device) and simple analyses (based on Banerjee's criteria) prove the magnetic-phase transformation from the first-order to the second-order, which takes place at a threshold value of d located in the range 60-70 nm. Compared with the as-prepared LCMO sample (a first-order magnetic phase transition), though the d decrease reduces the values of the T<SUB>C</SUB>, magnetization, magnetic-entropy change, and refrigerant capacity, but the width of the magnetic phase transition is increased remarkably. This widens the working range of LCMO NPs in magnetic refrigeration applications. We believe that the presence of surface-related effects, lattice strain, and distortions leads to Mn<SUP>3+</SUP>-Mn<SUP>4+</SUP> ferromagnetic interactions in LCMO NPs weaker than that in the as-prepared sample.</P>

First-to-second-order magnetic-phase transformation in La_0.7Ca_0.3-xBa_xMnO₃ exhibiting large magnetocaloric effect

Phan, T.L.,Dang, N.T.,Ho, T.A.,Manh, T.V.,Thanh, T.D.,Jung, C.U.,Lee, B.W.,Le, A.T.,Phan, A.D.,Yu, S.C. Elsevier Sequoia 2016 Journal of alloys and compounds Vol.657 No.-

We have prepared polycrystalline samples La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Ba<SUB>x</SUB>MnO<SUB>3</SUB> (x = 0, 0.025, 0.05, 0.075 and 0.1) by solid-state reaction, and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field (M-H-T) measurements. Experimental results reveal the easiness in tuning the Curie temperature (T<SUB>C</SUB>) from 260 to about 300 K by increasing Ba-doping concentration (x) from 0 to 0.1. Under an applied field H = 50 kOe, maximum magnetic-entropy changes around T<SUB>C</SUB> of the samples can be tuned in the range between 6 and 11 J kg<SUP>-1</SUP> K<SUP>-1</SUP>, corresponding to refrigerant-capacity values ranging from 190 to 250 J kg<SUP>-1</SUP>. These values are comparable to those of some conventional MC materials, and reveal the applicability of La<SUB>0.7</SUB>Ca<SUB>0.3-x</SUB>Ba<SUB>x</SUB>MnO<SUB>3</SUB> materials in magnetic refrigeration. Analyses of the critical behavior based on the Banerjee criteria, Arrott plots and scaling hypothesis for M-H-T data prove a magnetic-phase separation when Ba-doping concentration changes. In the doping region x = 0.05-0.075, the samples exhibits the crossover of first- and second-order phase transitions with the values of critical exponents β and γ close to those expected for the tricritical mean-field theory. The samples with x < 0.05 and x > 0.075 exhibit first- and second-order transitions, respectively. More detailed analyses related to the Griffiths singularity, the critical behavior for different magnetic-field intervals started from 10 kOe, and the magnetic-ordering parameter n = dLn|ΔS<SUB>m</SUB>|/dLnH (where ΔS<SUB>m</SUB> is the magnetic-entropy change) demonstrate magnetic inhomogeneities and multicritical phenomena existing in the samples.

Characteristics of critical current and index n of Bi-2223/Ag tape up to 30 T at 4.2 K

Kim, Jung Ho,Joo, Jinho,Choi, Seyong,Nah, W.,Ha, Dong-Woo,Ha, Hong-Soo,Matsumoto, A.,Kumakura, H.,Koizumi, T.,Sugano, M.,Kiyoshi, T. IEEE 2005 IEEE transactions on applied superconductivity Vol.15 No.2

We fabricated 55-filament Bi-2223/Ag tape and evaluated the dependence of critical current (I<SUB>c</SUB>) and index n in an external magnetic field up to 30 T at 4.2 K, in order to explore the possible application for a magnet in persistent current mode. I<SUB>c</SUB> and index n were characterized as a function of temperature and the magnitude and orientation of the magnetic field by increasing and decreasing field. It was observed that I<SUB>c</SUB> was dependent on the magnitude and orientation of the magnetic field. The I<SUB>c</SUB> decreased exponentially as the field increased; in a parallel and increasing field, I<SUB>c</SUB> was 128 A at 30 T, which is approximately 40% of the I<SUB>c</SUB> in self-field. On the other hand, index n was not significantly dependent on the field up to 30 T, nor did it vary significantly on increasing or decreasing field; the n value in the range of 0.1∼1 μV/cm was 23.0±5.2 and 27.8±8.0 on increasing and decreasing field, respectively, in the range of 0∼30 T. In addition, we observed that local I<SUB>c</SUB> and index n of a long length of tape (4.2 m) were dispersed over a wide range and that the variation of each of these two values with the position of the tape was similar, suggesting that these properties depend on the microstructural uniformity.

Stem cell transplant in the treatment of childhood biphenotypic acute leukemia

Park, Jeong A.,Ghim, Thad T.,Bae, Keun wook,Im, Ho Joon,Jang, Seong Soo,Park, Chan Jeong,Chi, Hyun Sook,Seo, Jong Jin Wiley Subscription Services, Inc., A Wiley Company 2009 Pediatric blood & cancer Vol.53 No.3

<B>Background</B><P>Many studies have found that biphenotypic acute leukemia (BAL) is associated with a poor outcome.</P><B>Methods</B><P>We retrospectively reviewed the medical records and analyzed clinicopathological data on 25 children with BAL, and correlated outcomes with prognostic factors.</P><B>Results</B><P>BAL constituted 4.4% of all acute childhood leukemia cases. In terms of immunophenotype, 14 patients had leukemia with myeloid plus B-lymphoid (M + B) marker, 7 with myeloid plus T-lymphoid (M + T) marker, and 4 with myeloid plus B-lymphoid and T-lymphoid (M + B + T) markers. Overall survival was superior in patients with the M + B immunophenotype (P = 0.004). Hematopoietic stem cell transplantation (HSCT) did not improve either overall survival or event-free survival compared to chemotherapy alone (hazard ratio 0.98, 95% CI 0.35–2.76, P = 0.966; hazard ratio 1.07, 95% CI 0.41–2.78, P = 0.88). Each of four patients with high-hyperdiploidy (>50 chromosomes) displayed a good treatment response and long-term overall survival even though these patients were treated with chemotherapy alone.</P><B>Conclusions</B><P>Treatment outcomes in childhood BAL patients differed by immunophenotype and cytogenetics. HSCT did not offer a significantly greater survival advantage compared to chemotherapy. While these data suggest that treatment should be individualized and stratified according to biologic characteristics and prognostic factors in BAL, prospective trial data are still needed. Pediatr Blood Cancer 2009;53:444–452. © 2009 Wiley-Liss, Inc.</P>

Magnetic Properties and Magnetocaloric Effect in Pb-Doped <inline-formula> <tex-math notation='TeX'> <tex> ${\rm La}_{0.9}{\rm Dy}_{0.1}{\rm MnO}_{3}$ </tex> </tex-math></inline-formula> Manganites

Ho, T. A.,Tran Dang Thanh,Thang, P. D.,Jong Suk Lee,Phan, T. L.,Seong Cho Yu IEEE 2014 IEEE transactions on magnetics Vol.50 No.6

<P>We have studied the magnetic properties and magnetocaloric effect of rhombohedral (La<SUB>0.9</SUB>Dy<SUB>0.1</SUB>)<SUB>1-x</SUB>Pb<SUB>x</SUB>MnO<SUB>3</SUB> (x = 0.1, 0.2, and 0.3) fabricated by solid-state reaction. Thermomagnetization curve reveals that the increase of Pb doping in (La<SUB>0.9</SUB>Dy<SUB>0.1</SUB>)<SUB>1-x</SUB>Pb<SUB>x</SUB>MnO<SUB>3</SUB> shifts the ferromagnetic (FM)-paramagnetic (PM) phase-transition temperature (T<SUB>C</SUB>) toward room temperature; the TCvalues determined for x = 0.1, 0.2, and 0.3 are about 172, 249, and 322 K, respectively. Based on magnetic-field dependencies of magnetization, M(H), the magnetic entropy changes (ΔS<SUB>m</SUB>) of the samples were calculated. Under an applied magnetic field of H = 10 kOe, the |ΔS<SUB>max</SUB>| value slightly increases from 0.74 J/kg · K for x = 0.1 to about 1.1 J/kg· K for x = 0.2 and 0.3. These results correspond to a relative cooling power of ~50 J/kg, which is comparable with some perovskite manganites, indicating the applicability of (La<SUB>0.9</SUB>Dy<SUB>0.1</SUB>)<SUB>1-x</SUB>Pb<SUB>x</SUB>MnO<SUB>3</SUB> in magnetic refrigeration devices working around room temperature. Particularly, we find that the variation of |ΔS<SUB>max</SUB>| versus the magnetic field H can be described by a power law |ΔS<SUB>max</SUB>| α Hn, where the magnetic-ordering parameter (n) decreases from 0.861 for x = 0.1-0.834 for x = 0.3. A deviation of the n values estimated from the mean-field theory (n = 2/3) demonstrates an existence of short-range FM order in the samples.</P>

Influence of Cr Doping on the Critical Behavior of Amorphous Alloy Ribbons Fe_{78–<i>x</i>}Cr_<i>x</i>Si₄Nb₅B₁₂Cu₁

Phan, T. L.,Thanh, P. Q.,Chau, N.,Huu, C. X.,Ngo, D.-T,Ho, T. A.,Thanh, T. D.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.11

<P>Though many previous works focused on studying Cr-doped Fe-Si-Nb-B-Cu amorphous alloys, magnetic-interaction mechanisms in these materials have not been carefully investigated yet. Dealing with these issues, we have prepared the amorphous alloy ribbons Fe<SUB>78-x</SUB>Cr<SUB>x</SUB>Si<SUB>4</SUB>Nb<SUB>5</SUB>B<SUB>12</SUB>Cu<SUB>1</SUB> with x= 1, 3, and 6, and then studied their magnetic and critical properties. Magnetization versus temperature and magnetic-field measurements, MHT, performed on a vibrating sample magnetometer reveal that the Cr-content increase in Fe<SUB>78-x</SUB>Cr<SUB>x</SUB>Si<SUB>4</SUB>Nb<SUB>5</SUB>B<SUB>12</SUB>Cu<SUB>1</SUB> reduces the T<SUB>C</SUB> from 430 K for x= 1 to about 322 K (for x= 6). This indicates the decline of ferromagnetic (FM) exchange interactions between Fe atoms when there is the presence of Cr atoms. We have also analyzed the M(H) data at the temperatures in the vicinity of the T<SUB>C</SUB> using the modified Arrott plot method and the scaling hypothesis, and determined the values of the critical exponents β = 0.367-0.376 and γ = 1.315-1.338. These values are close to those expected for the 3-D Heisenberg model with β = 0.365 and γ = 1.336, proving the existence of short-range FM order in the amorphous alloy ribbons.</P>

Influence of Ti Doping on the Critical Behavior and Magnetocaloric Effect in Disordered Ferromagnets La0.7Ba0.3Mn1−x Ti x O3

Ho, T. A.,Phan, M. H.,Phuc, N. X.,Lam, V. D.,Phan, T. L.,Yu, S. C. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.5

<P>The Ti-substitution influence on the magnetic and magnetocaloric properties of La0.7Ba0.3Mn1-x Ti (x) O-3 (x = 0.05 and 0.1) was investigated. Based on Banerjee's criteria and Franco's universal curves, we proved the existence of a second-order magnetic phase transition in the samples. Using the modified Arrott plot method, we determined the critical parameters T (C) a parts per thousand 245 K, beta = 0.374 +/- A 0.013, gamma = 1.228 +/- A 0.045, and delta = 4.26 +/- A 0.03 for x = 0.05, and T (C) a parts per thousand 169 K, beta = 0.339 +/- A 0.001, gamma = 1.307 +/- A 0.003, and delta = 4.78 +/- A 0.02 for x = 0.1. With these critical values, the predictable scaling behavior of the M(H) data above and below T (C) proves that the calculated exponents are unambiguous and intrinsic. The values beta = 0.374 for x = 0.05 and beta = 0.339 for x = 0.1 suggest that the magnetic phase transition of the samples falls into the three-dimensional (3D) Heisenberg and 3D Ising universality classes, respectively, corresponding to short-range ferromagnetic (FM) order due to FM clusters in a wide temperature range even above T (C), as confirmed by electron spin resonance studies. In reference to the magnetocaloric effect around T (C), the magnetic entropy change reaches maximum values (|Delta S-max|) of about 4 and 3 J kg(-1) K-1 for x = 0.05 and 0.1, respectively, for a magnetic field change 50 kOe. Magnetic field dependencies of |Delta S-max| obey a power function |Delta S-max(H)| ae H (n) , where exponent values n = 0.59 and 0.61 for x = 0.05 and 0.1, respectively, were determined from the relation n = 1 + (beta-1)/(beta + gamma). The difference between the experimental n values and the theoretical value n = 2/3 of the mean field model is due to the presence of short-range FM order in the samples.</P>

Influence of Pb Doping on the Magnetocaloric Effect and Critical Behavior of (La0.9Dy0.1)0.8Pb0.2MnO3

Ho, T. A.,Phan, T. L.,Thang, P. D.,Yu, S. C. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.5

<P>We used the modified Arrott plot method to analyze the magnetic field dependence of the magnetization, M(H), for a perovskite-type manganite (La0.9Dy0.1)(0.8)Pb0.2MnO3, and determined the critical parameter values T (C) = 248.4 K, beta = 0.484 +/- A 0.002, gamma = 0.961 +/- A 0.012, and delta = 2.90 +/- A 0.01. With these exponent values, the M(H) data around T (C) fall on two universal branches of a scaling function M(H,epsilon) = |epsilon| (beta) f (+/-)(H/|epsilon| (beta + gamma) ), where epsilon = (T - T (C))/T (C) is the reduced temperature, f (+) for T > T (C) and f (-) for T < T (C). Comparing with theoretical models, the exponent values obtained in our work are quite close to those expected from mean-field theory (with beta = 0.5, gamma = 1, and delta = 3). This reveals nearly long-range ferromagnetic order existing in (La0.9Dy0.1)(0.8) Pb0.2MnO3. From the M(H) data, we also found that, around the ferromagnetic-paramagnetic phase-transition temperature (T (C)), the magnetic entropy change reaches a maximum value (|delta S (max)|) of about 1.1 J kg(-1) K-1 for H = 10 kOe, corresponding to relative cooling power (RCP) of 50 J/kg. In addition to the above investigation, the temperature dependence of the magnetization, remanent magnetization (M (r)), and coercivity (H (c)) were recorded to learn about the physical processes taking place in (La0.9Dy0.1)(0.8)Pb0.2MnO3.</P>