Li-gang Zhang

Multiple magnetic transitions and large magnetoresistance of the Y0.5Ho0.5Mn6Sn6 compound

Magnetic transitions and magnetoresistance of the HfFe6Ge6-type Y0.5Ho0.5Mn6Sn6 compound have been investigated in the temperature range of 5–380 K. It was found that the compound displays paramagnetism, ferrimagnetism, antiferromagnetism, and reentrant ferrimagnetism with decreasing temperature. The temperature range of the antiferromagnetic state can be narrowed by increasing the magnetic field, and the metamagnetic transition from the antiferro- to ferrimagnetic state can be induced by a fairly small threshold field (<6 kOe). The antiferro-ferrimagnetic transition is accompanied by a large magnetoresistance effect of about −16% at 100 K. The magnetic transitions with temperature and magnetic field are both of the second order.

Unusual magnetic and transport properties of layered compound ErMn6Sn6

The magnetic and magnetotransport properties of the polycrystalline ErMn6Sn6 compound have been investigated in the temperature interval of 5–380 K. The compound shows paramagetism, antiferromagnetism, and ferrimagnetism with decreasing temperature. In the antiferromagnetic state (67–362 K), the transition from antiferromagnetism to ferrimagnetism can be induced by an applied field, and the metamagnetic transition field increases from 0.2 kOe at 80 K to 15 kOe around 200 K and then decreases monotonously to 5 kOe at 330 K. The large magnetoresistance {MR=[R(H)−R(0)]×100%/R(0)} effect is observed with the metamagnetic behavior, such as −9.8% at 135 K under a field of 50 kOe. It is worth noting that ErMn6Sn6 displays the positive MR in the ferrimagnetic state and the negative one in the antiferromagnetic state, respectively, and the origin of the MR anomalies has been discussed.

Magnetism and giant magnetoresistance of HeFe6Ge6-type Y0.7Ce0.3Mn6Sn6 compound

Magnetic transitions and magnetoresistance (MR) effect of the HfFe6Ge6-type Y0.7Ce0.3Mn6Sn6 compound have been investigated in the temperature range of 5–370 K. The sample undergoes paramagnetic, ferrimagnetic, and antiferromagnetic ordering with cooling. In the antiferromagnetic state, a moderate magnetic field (⩽11 kOe) is sufficient to switch Y0.7Ce0.3Mn6Sn6 from the antiferromagnetic to ferrimagnetic state, and this results in the giant magnetoresistance effect of −36.5∼−6% from 5 K to 285 K at 50 kOe. It is found that the MR (MR=[ρ(H)−ρ(0)]/ρ(0)×100%) behavior of the sample can be expressed as MR=−A(M/MS)2 in the field range from antiferromagnetic to ferrimagnetic configuration, and the power-law magnetic-field dependence of the MR effect MR∝−Hq is shown in the ferrimagnetic state. The values of the exponent q are 0.35, 0.46, and 0.65 at 5 K, 75 K, and 285 K, respectively.

Structure and magnetic properties of ( x = 0-3) compounds with R = Y and Pr

The influence of Si substitution for Co on the structure and magnetic properties of and (x = 0-3) compounds were investigated by means of x-ray diffraction and magnetization measurements. X-ray diffraction patterns demonstrate that all samples are single phase with the hexagonal -type structure for and the rhombohedral -type structure for compounds, except for with a small amount of impurity phases. The unit-cell volume is found to decrease linearly with increasing Si concentration in both series. The Curie temperature decreases monotonically with increasing Si concentration at an approximate rate of 205 and 175 K per Si atom for the and compounds, respectively. The saturation magnetic moments of (R = Y, Pr) decrease with increasing Si content and the decline rates are larger than that expected as a simple dilution. For , the substitution of Si has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, and changes the easy magnetization direction from the basal plane to the c-axis at room temperature. For , the Si substitution has not changed the easy magnetization direction at room temperature. However, the spin-reorientation transitions from the basal plane to the c-axis for this series with were observed above room temperature with increasing temperature. The spin-reorientation temperature first decreases with increasing Si content and then increases at higher x values (x > 2). The origin of this spin reorientation is interpreted by the competition between the Pr sublattice anisotropy and the Co sublattice anisotropy. This has been confirmed by the magnetocrystalline anisotropy measurements on .

Magnetism and magnetoresistance of Dy1−xSmxMn6Ge6 (x = 0.2–1.0) compounds

The magnetic and transport properties of Dy1−xSmxMn6Ge6 (x = 0.2–1.0) have been investigated using x-ray diffraction (XRD) and magnetization measurements. Analysis of the XRD patterns indicates that the samples with x ≤ 0.4 mainly consist of the HfFe6Ge6-type phase and the samples with 0.6 ≤ x ≤ 1.0 mainly consist of the YCo6Ge6-type phase (P6/mmm). The lattice constants and the unit cell volume increase with increasing Sm content. The antiferro–ferri–ferromagnetic transition can be observed with increasing Sm content. The samples with x = 0.2 and x = 0.4 order antiferromagnetically at 425 K and 430 K, respectively, and there are the second magnetic phase transitions below 50 K. The sample with x = 0.6, 0.8 and 1.0 become ferri- to ferromagnetically ordered over the whole magnetic ordering temperature range. The corresponding Curie temperatures are 445 K, 450 K and 454 K, respectively. The magnetoresistance (MR) curve of the sample with x = 0.6 in applied magnetic fields of up to 5 T is analysed. The inflexions in the MR–H curves can be interpreted as being due to the influence of the magnetic field on the Fermi surface or due to the competition between the scattering of the magnetic moments and the effect of the Lorentz force on the conduction electrons.

Magnetism and magnetoresistance studies of HfFe6Ge6-type Y1-xCexMn6Sn6 (x=0.1-0.3) compounds

Magnetic transitions and the magnetoresistance (MR) effect of the HfFe6Ge6-type Y1-xCexMn6Sn6 (x=0.1-0.3) compounds have been investigated in the temperature range of 5-385 K. Y0.9Ce0.1Mn6Sn6 and Y0.825Ce0.175Mn6Sn6 show antiferromagnetism and Y0.7Ce0.3Mn6Sn6 undergoes an antiferromagnetic (AFM) to ferrimagnetic (Fi) transition with increasing temperature. The metamagnetic transition from helical antiferromagnetism to ferrimagnetism can be also induced by an applied field for those compounds. The metamagnetic transition field decreases with increasing Ce content, such as from 25 kOe for x=0.1 to 11 kOe for x=0.3 at 5 K. The giant MR (GMR) effect for Y1-xCexMn6Sn6 (x=0.1-0.3) is observed with metamagnetic behaviour, such as -37% at 5 K under a field of 50 kOe for the compounds (x=0.175 and 0.3). It is found that the MR behaviour for Y0.7Ce0.3Mn6Sn6 in the Fi state follows the magnetic-field power law MR proportional to-H-q at a fixed temperature, and obeys the relationship MR=-[alpha+beta/(T+gamma)] under a fixed magnetic field.

Magnetization and magnetoresistance studies of HfFe6Ge6-type Y1-xLaxMn6Sn6 (x = 0.1 and 0.2) compounds

Magnetic transitions and the magnetoresistance effect of the HfFe6Ge6-type Y1−xLaxMn6Sn6 (x = 0.1 and 0.2) compounds have been investigated in the temperature range 5–385 K. The samples display an antiferromagnetic behaviour in the whole magnetic ordering temperature range, and their Neel temperature is 309 K and 323 K for x = 0.1 and 0.2, respectively. The metamagnetic transition from antiferromagnetism to ferromagnetism can be induced by an applied field. The metamagnetic transition field varies from 20 kOe at 5 K to 4 kOe at 300 K. The giant magnetoresistance effect is observed with the metamagnetic behaviour, such as −10.4% at 245 K for x = 0.1 under 50 kOe. Interestingly, the positive magnetoresistance for x = 0.2 appears below 110 K.

Multiple magnetic transitions and large magnetoresistance of Y0.8Dy0.2Mn6Sn6 compound

Magnetic transitions and magnetoresistance of HfFe6Ge6-type Y0.8Dy0.2Mn6Sn6 compound have been investigated in the temperature range of 5–375 K. It was found that the compound displays paramagnetism, ferrimagnetism, antiferromagnetism, and reentrant ferrimagnetism with decreasing temperature. At low temperatures, the strong exchange interaction between the Dy and Mn sublattices results in ferrimagnetism. The metamagnetic transition from the antiferro- to ferrimagnetic state can be induced by a fairly small threshold field (⩽7 kOe). The magnetic transition is accompanied by a large magnetoresistance effect of about −29% and −7% at 5 and 293 K, respectively.

Magnetocrystalline anisotropy of Ho2(Co1-xFex)15Al2 compounds

The structure and magnetic properties of Ho2(Co1-xFex)15Al2 compounds with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1.0 have been investigated by x-ray diffraction (XRD) and magnetization measurements. XRD patterns demonstrate that all samples are single phase with the hexagonal Th2Ni17-type structure. The substitution of Fe for Co leads to a nearly linear increase in the unit cell volume and a monotonic decrease of Curie temperature. Saturation magnetization increases with x and then decreases, attaining a maximum at x = 0.2. The magnetic anisotropy phase diagram of Ho2(Co1-xFex)15Al2 compounds has been determined from the temperature dependence of magnetization and the XRD patterns of magnetically oriented powder samples. The spin-reorientation temperature of Ho2(Co1-xFex)15Al2 compounds was found to decrease firstly with Fe content increasing for x<0.1 and then increase for 0.1

Structure and magnetic properties of Y1-xDyxMn6Sn6 (x = 0-1) compounds

The structure and magnetic properties of Y1-xDyxMn6Sn6 (x = 0-1) compounds have been studied by x-ray diffraction and magnetization measurements. All studied samples crystallize in HfFe(6)GC(6)-type structure (space group P6/mmm). The compound with x = 0 behaves as anti-ferromagnetic behaviour, and the compounds (x = 0.6-1) display ferrimagnetic behaviours in the whole magnetic ordering temperature range. The compounds (x = 0.2-0.4) exhibit a transition from ferrimagnetic to anti-ferromagnetic, then to ferrimagnetic state again with increasing temperature. The magnetization curves of compounds (x = 0.3-1) at 5 K almost saturate at 5 T, and the saturation magnetization M-s decreases with increasing Dy content. The compounds (x = 0-0.3) display field-induced metamagnetic transition, and the threshold field decreases with increasing Dy content. The unit-cell volume V of Y1-x,DyxMn6Sn6 (x = 0-1) compounds decreases. and the ordering points increase with increasing Dy content.