Author(s): Mohamed El Gazzah
Mentor(s): Nirmal Ghimire, Physics and Astronomy
AbstractThis project is about manipulating magnetic structure in the compound TmMn6Sn6.through chemical substitution of Sn by Ga. The compound TmMn6Sn6 has hexagonal crystal structure and orders into a quite complicated spiral magnetic state below its Neel temperature of 347 K. Literature search shows that TmMn6Sn6-xGax compounds were studied in polycrystalline form and by magnetometry and neutron powder diffraction experiments where an intriguing magnetic structure consisting of three helices propagating along the crystallographic c-axis was found in the parent compound TmMn6Sn6. This spin structure changes considerably with the Ga doping. Our motivation was to study these compounds and test whether the manipulation of the magnetic interaction through Ga doping, can stabilize any intriguing magnetic structures. Here we grew single crystals of four different compositions TmMn6Sn6-x with x = 0, 0.5, 1.0. and 1.3, and characterized the crystals by analyzing crystal structure by means of x-ray powder diffraction. We studied magnetic properties by measuring magnetic susceptibility of all four compositions. With increasing Ga concentration both lattice parameters a and c decrease thus decreasing the volume. This essentially changes the strength of magnetic interaction between different magnetic layers, thus changes the magnetic properties. With Ga doping the magnetic transition temperature changes slightly. For the concentrations x = 0, 0.5 and 1, the moments remain in the ab-plane down to 1.8 K. For the composition with x =1.3, the spins are in the plane below the Neel temperature. But when the temperature is lowered at around 250 K, the spins rotate from the basal plane towards the c-axis. Future works are to measure magnetization, and Hall effect in these compositions to look for the spin textures that can be manipulated more easily by external stimuli such as magnetic field and current.
Audio TranscriptHello everyone, my name is Mohamed El Gazzah. Today I will be talking about my project, which is on the synthesis and magnetic study of TmMn6Sn6-xGax.
Modern electronics use silicon chips, which are currently facing difficulties in making faster, thinner and more energy efficient devices. Silicon chips use the charge of electrons to process information. However electrons also have a property called spin. In magnetic materials electron’s spin can order over a long-range making magnetic structures. The conventional magnetic structures such as in iron, are difficult to manipulate with electric current. So, there is a great deal of interest in new forms of magnetic structures that can be easily manipulated and can thus be applied in spin based electronics.
I researched this particular compound because an interesting magnetic property was reported in polycrystalline form. However, to completely understand the magnetism and look for potentially interesting magnetic structures, studies in single crystalline form are required.
This is the schematic of the crystal structure of TmMn6Sn6. It consists of Thulium and Manganese, which are both magnetic and form layers going along the c axis. The green sphere is Thulium, black is Manganese, and the rest are tin. Tin in this particular layer can be replaced by Gallium which has a smaller atomic radius than Tin. The gallium doping will then change the magnetic interaction between different layers and allows us to manipulate the magnetic structure. Our goal is to manipulate the spirals in the parent compound to stabilize a magnetic structure that potentially can be manipulated easily.
To synthesize my crystals, I used the flux method where the elements are added into a crucible and put through a series of changes in temperature. Here the flux is Tin since it allows the other elements to melt at a much lower temperature. The reaction was carried out in an non-reactive atmosphere inside a furnace shown here. Sn dissolves both Tm and Mn below their melting point and allows all the elements to combine and form a solution. Then lowering the temperature oversaturates the solution and the crystals form. That can be seen in this figure.
The compositions I grew included TmMn6Sn6, TmMn6Sn5.5Ga0.5, TmMn6Sn5Ga1, and TmMn6Sn1.7Ga1.3
The structure of the crystals was then verified through x-ray powder diffraction which gave the data shown in this figure. After verifying the structure and learning the composition, I then measured the magnetic properties of the crystals. The following figure shows the data I got using the quantum design PPMS available at the Ghimire Lab.
What we see here is that all the compounds show a sharp change between 350K and 375 K, which we can be seen on both figures. This is the temperature at which the compounds become magnetic. In the top figure, the overall magnetic moment is larger for all composition except 1.3 when compared to the bottom figure. This tells us that the spins in these compositions are in the plane. When looking at composition x=1.3 shown in green, in the top figure the moment is large above 200K and small below that, but in the bottom figure the opposite behavior is seen. This tells us about the spins from 200 to 350 kelvin are in the plane, but when the temperature is below that, the spins re-orient out of plane.
As of this semester I have been able to grow the crystals, verify them, and measure some of their magnetic properties. However, there are several things yet to be done, such as measuring magnetization, resistivity and Hall effect. This will tell us if there any interesting magnetic structures and following that neutron diffraction experiments can be done which will allow us to figure out the nature of the magnetic structures. I would like to thank my mentor Dr. Ghimire for helping me conduct this research and I would like to thank Hari Bhandari and Peter Siegfried for their assistance in and out of the lab. Thank you very much for listening.
Modern electronics use silicon chips, which are currently facing difficulties in making faster, thinner and more energy efficient devices. Silicon chips use the charge of electrons to process information. However electrons also have a property called spin. In magnetic materials electron’s spin can order over a long-range making magnetic structures. The conventional magnetic structures such as in iron, are difficult to manipulate with electric current. So, there is a great deal of interest in new forms of magnetic structures that can be easily manipulated and can thus be applied in spin based electronics.
I researched this particular compound because an interesting magnetic property was reported in polycrystalline form. However, to completely understand the magnetism and look for potentially interesting magnetic structures, studies in single crystalline form are required.
This is the schematic of the crystal structure of TmMn6Sn6. It consists of Thulium and Manganese, which are both magnetic and form layers going along the c axis. The green sphere is Thulium, black is Manganese, and the rest are tin. Tin in this particular layer can be replaced by Gallium which has a smaller atomic radius than Tin. The gallium doping will then change the magnetic interaction between different layers and allows us to manipulate the magnetic structure. Our goal is to manipulate the spirals in the parent compound to stabilize a magnetic structure that potentially can be manipulated easily.
To synthesize my crystals, I used the flux method where the elements are added into a crucible and put through a series of changes in temperature. Here the flux is Tin since it allows the other elements to melt at a much lower temperature. The reaction was carried out in an non-reactive atmosphere inside a furnace shown here. Sn dissolves both Tm and Mn below their melting point and allows all the elements to combine and form a solution. Then lowering the temperature oversaturates the solution and the crystals form. That can be seen in this figure.
The compositions I grew included TmMn6Sn6, TmMn6Sn5.5Ga0.5, TmMn6Sn5Ga1, and TmMn6Sn1.7Ga1.3
The structure of the crystals was then verified through x-ray powder diffraction which gave the data shown in this figure. After verifying the structure and learning the composition, I then measured the magnetic properties of the crystals. The following figure shows the data I got using the quantum design PPMS available at the Ghimire Lab.
What we see here is that all the compounds show a sharp change between 350K and 375 K, which we can be seen on both figures. This is the temperature at which the compounds become magnetic. In the top figure, the overall magnetic moment is larger for all composition except 1.3 when compared to the bottom figure. This tells us that the spins in these compositions are in the plane. When looking at composition x=1.3 shown in green, in the top figure the moment is large above 200K and small below that, but in the bottom figure the opposite behavior is seen. This tells us about the spins from 200 to 350 kelvin are in the plane, but when the temperature is below that, the spins re-orient out of plane.
As of this semester I have been able to grow the crystals, verify them, and measure some of their magnetic properties. However, there are several things yet to be done, such as measuring magnetization, resistivity and Hall effect. This will tell us if there any interesting magnetic structures and following that neutron diffraction experiments can be done which will allow us to figure out the nature of the magnetic structures. I would like to thank my mentor Dr. Ghimire for helping me conduct this research and I would like to thank Hari Bhandari and Peter Siegfried for their assistance in and out of the lab. Thank you very much for listening.
4 replies on “Crystal Growth and Magnetic Measurement of TmMn6Sn6-xGax”
Nice presentation. You talked about the next things you want to study with this compound. Do you plan to do that next semester or move on to a different compound?
Hi Dr. Lee, thank you so much for your reply. I plan on applying for a mini-grant for the coming semester to continue my research on this same compound. I would just like to grow various ne compositions which I believe would produce interesting results and also study those.
Great work, Mohamed! I’m impressed and intrigued by the crystals you’ve grown! Does research about this particular compound lay the foundation for furture work you’ll conduct?
Hi Mrs. Rahman, thank you so much for your comment. This research is a gateway to understanding so much more about this material, I have only shown that there may be interesting characteristics by studying its magnetism and verifying the compositions. The future work would include different types of measurements such as the Hall effect measurement and neutron diffraction experiment. This will allow me to understand what’s really going in within the magnetism of this material.