A Vernière

High rare earth sublattice ordering temperatures in new CeFeSi-type RTiGe (R≡La-Nd, Sm) compounds

Investigations made by powder X-ray diffraction and susceptibility measurements on ternary germanides RTiGe (R≡La–Nd, Sm, Lu) are reported. All these new compounds crystallize in the well-known tetragonal structure of the CeFeSi-type (space group P4/nmm). LaTiGe and LuTiGe are Pauli paramagnets. CeTiGe is characterized by Curie–Weiss paramagnetism down to 5 K, whereas PrTiGe, NdTiGe and SmTiGe behave antiferromagnetically below 70, 150 and 265 K, respectively. Low temperature (T<77 K) investigations of the corresponding heavy rare earth compounds show that ErTiGe and TmTiGe are antiferromagnetic below 41 and 15 K, respectively. Metamagnetic-like behaviour occurs in ErTiGe, TmTiGe (Hc≅2 kOe) and HoTiGe (Hc≅5 kOe). These results are discussed and compared with those of isotypic ternary RTX (T≡Mn, Fe, Co, Ru; X≡Si, Ge) compounds.

Magnetic properties of HfFe6Ge6-type LuMn6Sn6−xInx compounds (0.1≤x≤2.0)

Abstract The HfFe 6 Ge 6 -type LuMn 6 Sn 6− x In x compounds (0.1≤ x ≤2.0) have been synthesized and studied by powder magnetization measurements. The compounds with low In content ( x In ≤0.6) order antiferromagnetically with Neel temperatures decreasing from 380 K for x =0.2 to 282 K for x =0.6. The In-rich compounds (1.2≤ x In ≤2.0) display ferromagnetic behaviors in their whole ordered range with Curie temperatures decreasing from 263 K for x =1.2 to 221 K for x =2.0. The compounds of intermediate compositions ( x In =0.8 and 1.0) order ferromagnetically at T c =280 and 278 K, respectively, and undergo a ferro- to antiferromagnetic transition on cooling ( T t =248 and 151 K, respectively). The variation of the threshold fields confirms the increase of the antiferromagnetic character on cooling. These results are discussed and compared with the different behaviors observed for the corresponding LuMn 6 Ge 6− x Ga x solid solution.

A neutron diffraction study of HfFe6Ge6-type YMn6Sn6−xInx compounds (0.03≤x≤0.72)

Abstract The HfFe 6 Ge 6 -type YMn 6 Sn 6− x In x compounds ( x =0.03, 0.10, 0.23, 0.37, 0.72) have been studied by means of magnetization measurements and powder neutron diffraction studies. YMn 6 Sn 5.97 In 0.03 and YMn 6 Sn 5.90 In 0.10 display helimagnetic order over their entire ordered temperature range ( T N =330 and 334 K, respectively). YMn 6 Sn 5.77 In 0.23 and YMn 6 Sn 5.63 In 0.37 order ferromagnetically ( T c =324 and 323 K, respectively) and undergo a ferro- to helimagnetic transition below T t =308 and 258 K. YMn 6 Sn 5.28 In 0.72 displays ferromagnetic order over its entire ordered temperature range ( T c =312 K). In the helimagnetic state, unusual thermal variations of the q z component of the propagating vector were observed with Δ q z /Δ T >0 for x =0.03 and 0.10 and Δ q z /Δ T x =0.23 and 0.37.

Magnetic properties of HfFe6Ge6-type ScMn6Sn6-xInx and YMn6Sn6-xInx compounds (0.1≤x≤1.0)

Abstract The HfFe 6 Ge 6 -type ScMn 6 Sn 6− x In x and YMn 6 Sn 6− x In x compounds (0.1≤ x ≤1.0) have been synthesized and studied by powder X-ray diffraction, microprobe analysis and magnetization measurements. The low In content compounds ScMn 6 Sn 5.88 In 0.12 and YMn 6 Sn 5.89 In 0.11 order antiferromagnetically at T N =381 and 334 K, respectively. The In-rich compounds ( x ≥0.61) are ferromagnetic in their whole ordered range (297≤ T c ≤359 K). Compounds of intermediate compositions order ferromagnetically above room temperature and undergo a ferro- to antiferromagnetic transition on cooling. The results are discussed and compared with those observed for the other HfFe 6 Ge 6 -type LuMn 6 Sn 6− x In x and RMn 6 Ge 6− x Ga x (R=Sc, Y, Lu) solid solutions.

Single crystal refinements of TbTiGe, GdTiGe and TbTi0.85Mo0.15Ge with CeFeSi- and CeScSi-type structures

Abstract The atomic coordinates of the TbTi 0.85 Mo 0.15 Ge, GdTiGe and TbTiGe compounds have been refined from single crystal X-ray diffraction measurements. Both former compounds have a tetragonal CeScSi-type structure ( I4/mmm , ordered variant of the La 2 Sb-type) while TbTiGe crystallizes in the CeFeSi-type ( P4/nmm ). The structural properties and the relative stability of both CeFeSi and CeScSi-type structures along the whole RTiGe series (R=La–Nd, Sm, Gd–Tm, Lu) are discussed and compared to those of others isotypic RTX compounds.

Multi spin-reorientation process in HfFe6Ge6-type HoMn6Ge6−xGax compounds (x=0.2, 0.4, 1.0)

Abstract The HoMn 6 Ge 6− x Ga x compounds ( x =0.2, 0.4, 1.0) have been studied by magnetization measurements and neutron diffraction in the temperature range 2–300 K. The HoMn 6 Ge 5.8 Ga 0.2 compound orders antiferromagnetically at 415 K and displays a Curie point at 72 K. Neutron diffraction indicates a helimagnetic structure from 300 to 72 K and a cone structure at lower temperature ( μ Mn =2.23(6) μ B and μ Ho =9.46(12) μ B at 2 K). The HoMn 6 Ge 5.6 Ga 0.4 compound orders antiferromagnetically at 395 K. Neutron diffraction study indicates a helimagnetic structure between 250 and 300 K, a ferrimagnetic structure with moments almost aligned along the c -axis between 225 and 180 K, a cone structure in the temperature range 180–70 K and finally a ferrimagnetic structure below 70 K. At 2 K, the moment direction is at 43(1)° from the c -axis ( μ Mn =2.18(6) μ B and μ Ho =9.59(9) μ B . The HoMn 6 Ge 5 Ga compound is ferrimagnetic in its whole ordered range ( T C =378 K). At room temperature, the moment direction is at 60(4)° from the c -axis and rotates continuously towards the c -axis on cooling. In the 250–150 K temperature range, the moments are almost aligned along the c -axis and rotate again towards the (001) plane at lower temperature. At 2 K, the moment direction is at 46(1)° from the c -axis ( μ Mn =2.28(5) μ B and μ Ho =9.81(9) μ B at 2 K). The anomalous variation of the moment direction is discussed and related to the successive effect of the second and fourth order crystalline field parameters. The evolution of the magnetic order as a function of the Ga content is examined and comparisons are made with the RMn 6 Ge 6− x Ga x compounds (R=Lu, Tm).

Neutron diffraction study of HfFe6Ge6-type TmMn6Ge6-xGax compounds (x=0.2, 0.4, 0.6, 0.8 and 1.0)

Abstract The TmMn 6 Ge 6− x Ga x compounds ( x =0.2, 0.4, 0.6, 0.8 and 1.0) have been investigated by magnetization measurements and neutron diffraction. The TmMn 6 Ge 5.8 Ga 0.2 compound orders antiferromagnetically at 471 K in a colinear magnetic structure characterized by a doubling of the c axis. Below T t =220 K, a helimagnetic structure takes place. At 2 K, the spiral plane lies in the (101) plane with μ Mn =2.02(5) μ B and μ Tm =6.27(9) μ B . The TmMn 6 Ge 5.6 Ga 0.4 compound orders antiferromagnetically at 402 K. From 300 to 42 K, it is characterized by a helimagnetic arrangement with a helical plane lying in the (101) plane. Below 42 K, a conical structure takes place and the direction of the ferromagnetic component is almost aligned along the c axis. The Mn and Tm moments refined at 2 K are μ Mn =2.21(5) μ B and μ Tm =6.82(8) μ B . The TmMn 6 Ge 5.4 Ga 0.6 compound orders antiferromagnetically at 379 K. From 300 to 124 K, it is characterized by a helimagnetic arrangement with a helical plane close to the (001) plane. Below 124 K, this compound becomes ferrimagnetic with moments almost aligned along the c axis. The Mn and Tm moments refined at 2 K are μ Mn =2.19(4) μ B and μ Tm =6.89(7) μ B . The TmMn 6 Ge 5.2 Ga 0.8 and TmMn 6 Ge 5 Ga compounds order ferrimagnetically at 360 and 359 K, respectively, and a moment reorientation takes place at 73 and 56 K, respectively. At high temperature the moments are close to the (001) plane whereas at low temperature they almost align along the c axis in good agreement with the large coercive field reported at 4.2 K for this compound ( H c ≈20 kOe). The Mn and Tm moments refined at 2 K are μ Mn =2.20(5)μ B [2.18(4)] and μ Tm =7.01(8) μ B [7.01(8)], respectively. The evolutions of the moment magnitudes, magnetocrystalline anisotropy and interlayer couplings, as a function of the Ga content, are discussed.

New AlB2- and GdSi2-type derivative compounds in the Y-Ga-Ge system

Abstract The Y–Ge–Ga system has been investigated by powder X-ray diffraction and microprobe analysis. Three new AlB 2 - and two new GdSi 2 -type derivative compounds have been characterized. The structure of the Y 8 (Ge,Ga) 15− x compound (space group: P 6 3 / mmc ; a =8.097(2) A, c =16.464(4) A) has been refined from powder diffraction data. The analysis of the results clearly indicates a reduction of the non-metal vacancies with the gallium content.

Electronic structure and magnetic properties of RMnX (R=Mg, Ca, Sr, Ba, Y; X=Si, Ge) studied by KKR method

Abstract.Electronic structure calculations, using the charge and spin self-consistent Korringa- Kohn-Rostoker (KKR) method, have been performed for several RMnX compounds (R = Mg, Ca, Sr, Ba, Y; X = Si, Ge) of the CeFeSi-type structure. The origin of their magnetic properties has been investigated emphasizing the role of the Mn sublattice. The significant influence of the Mn-Mn and Mn-X interatomic distances on the Mn magnetic moment value is delineated from our computations, supporting many neutron diffraction data. We show that the marked change of

Crystallographic data and magnetic properties of new ThSi2 and GdSi2 derivative compounds in the Gd-Ga-Ge system

\mu_{\rm Mn}