{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/141583"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/141583","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Practical Pathways to Efficient MRAM: Spin-Orbit Torques, Low-Damping, and Anomalous Hall Conductivity in Polycrystalline Materials","abstract":"There are multiple pathways forward to next generation magnetic random access memory. In this thesis we explore two simple solutions with industry implementation in mind. The first is a low-damping (α< 5×10⁻³) ferromagnetic single-layer with modest anti-damping spin-orbit torque (SOT), $θ_{DL} ≈ 0.05. Here, we investigate an alternative approach to the traditional heavy metal/ferromagnet bilayer to produce SOTs, which suffers from high-damping that is detrimental to energy-efficiency. Instead, of breaking inversion symmetry at the interface we continually break symmetry along the thickness axis by creating an intentional compositional gradient that is purely ferromagnetic and maintains low damping. Crucially, we find that a compositional gradient is not necessary to achieve large damping-like SOTs, instead finding direct evidence from grazing-incidence x-ray diffraction for a strain gradient. The next pathway investigated is an easy-to-grow, polycrystalline alternative to non-collinear antiferromagnets which require high temperature growth (>400°C). We find that sputter-grown γ-FeMn with no post-annealing, has a small non-zero net magnetization (≈(0.02-0.07)μB/atom) and perpendicular magnetic anisotropy only slightly larger than those found in non-collinear antiferromagnets like Mn₃Sn while still exhibiting a large anomalous Hall conductivity of 14 S/cm at room temperature. We show that these unique magnetic and transport properties are the result of pinning at the grain boundaries which can be tuned to enhance the anomalous Hall conductivity.","abstract_html":"There are multiple pathways forward to next generation magnetic random access memory. In this thesis we explore two simple solutions with industry implementation in mind. The first is a low-damping (α&lt; 5×10⁻³) ferromagnetic single-layer with modest anti-damping spin-orbit torque (SOT), $θ_{DL} ≈ 0.05. Here, we investigate an alternative approach to the traditional heavy metal/ferromagnet bilayer to produce SOTs, which suffers from high-damping that is detrimental to energy-efficiency. Instead, of breaking inversion symmetry at the interface we continually break symmetry along the thickness axis by creating an intentional compositional gradient that is purely ferromagnetic and maintains low damping. Crucially, we find that a compositional gradient is not necessary to achieve large damping-like SOTs, instead finding direct evidence from grazing-incidence x-ray diffraction for a strain gradient. The next pathway investigated is an easy-to-grow, polycrystalline alternative to non-collinear antiferromagnets which require high temperature growth (&gt;400°C). We find that sputter-grown γ-FeMn with no post-annealing, has a small non-zero net magnetization (≈(0.02-0.07)μB/atom) and perpendicular magnetic anisotropy only slightly larger than those found in non-collinear antiferromagnets like Mn₃Sn while still exhibiting a large anomalous Hall conductivity of 14 S/cm at room temperature. We show that these unique magnetic and transport properties are the result of pinning at the grain boundaries which can be tuned to enhance the anomalous Hall conductivity.","abstract_has_math":false,"creators":["Maizel, Rachel Emily"],"institution":"Virginia Tech","degree_name":"Doctor of Philosophy","degree_level":"doctoral","degree_discipline":"Physics","degree_department":"Physics","school":null,"contributors":[],"advisors":[],"committee_chairs":["Emori, Satoru"],"committee_members":["Heremans, Jean Joseph","Ashkar, Rana","Ivanov, Vsevolod Mikhailovich"],"year":2026,"date_issued":"2026-02-26","date_published":"2026-02-26","updated_at":"2026-07-22T22:20:05Z","subjects":["Spintronics","Anomalous Hall Effect","Spin Hall Effect","FMR","ST-FMR","antiferromagnets","low-damping"],"languages":["en"],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45716"],"render_values":[{"text":"vt_gsexam:45716","href":null,"code":true}]}]},"links":{"outbound_url":"https://hdl.handle.net/10919/141583","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Emori, Satoru"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Heremans, Jean Joseph","Ashkar, Rana","Ivanov, Vsevolod Mikhailovich"]},{"key":"dc:contributor.department","label":"Department","values":["Physics"]},{"key":"dc:creator","label":"Author","values":["Maizel, Rachel Emily"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-02-27T09:00:15Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-02-27T09:00:15Z"]},{"key":"dc:date.issued","label":"Date","values":["2026-02-26"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Spintronics","Anomalous Hall Effect","Spin Hall Effect","FMR","ST-FMR","antiferromagnets","low-damping"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:45716"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10919/141583"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["There are multiple pathways forward to next generation magnetic random access memory. In this thesis we explore two simple solutions with industry implementation in mind. The first is a low-damping (α< 5×10⁻³) ferromagnetic single-layer with modest anti-damping spin-orbit torque (SOT), $θ_{DL} ≈ 0.05. Here, we investigate an alternative approach to the traditional heavy metal/ferromagnet bilayer to produce SOTs, which suffers from high-damping that is detrimental to energy-efficiency. Instead, of breaking inversion symmetry at the interface we continually break symmetry along the thickness axis by creating an intentional compositional gradient that is purely ferromagnetic and maintains low damping. Crucially, we find that a compositional gradient is not necessary to achieve large damping-like SOTs, instead finding direct evidence from grazing-incidence x-ray diffraction for a strain gradient. The next pathway investigated is an easy-to-grow, polycrystalline alternative to non-collinear antiferromagnets which require high temperature growth (>400°C). We find that sputter-grown γ-FeMn with no post-annealing, has a small non-zero net magnetization (≈(0.02-0.07)μB/atom) and perpendicular magnetic anisotropy only slightly larger than those found in non-collinear antiferromagnets like Mn₃Sn while still exhibiting a large anomalous Hall conductivity of 14 S/cm at room temperature. We show that these unique magnetic and transport properties are the result of pinning at the grain boundaries which can be tuned to enhance the anomalous Hall conductivity."]},{"key":"dc:description.abstractgeneral","label":"General Abstract","values":["The spintronics community is searching for ways to make denser, faster, more power efficient and better enduring magnetic memory that can keep up with modern needs. One hurdle that this thesis addresses is how to minimize dissipation lost by magnetic friction while maintaining fast writing capabilities. The next is the issue of denser bits for magnetic memory, traditional ferromagnets have a stray field, like a horseshoe magnet in a sea of lead, which affects nearby components. This limits how tightly we can pack the bits that store our \"1\"s and \"0\"s in magnetic memory. An alternative path forward that is gaining interest is using antiferromagnets in magnetic memory as they have reduced stray fields. However, one of the issues is that because they do not have a large magnetic moment like in ferromagnets it can be hard to read the \"1\" and \"0\" states. This thesis offers a practical step forward with an inexpensive, easy-to-grow antiferromagnet that has the potential for large readout capabilities."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Doctor of Philosophy"]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Practical Pathways to Efficient MRAM: Spin-Orbit Torques, Low-Damping, and Anomalous Hall Conductivity in Polycrystalline Materials"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Emori, Satoru"],"dc:contributor.committeemember":["Heremans, Jean Joseph","Ashkar, Rana","Ivanov, Vsevolod Mikhailovich"],"dc:contributor.department":["Physics"],"dc:creator":["Maizel, Rachel Emily"],"dc:date.accessioned":["2026-02-27T09:00:15Z"],"dc:date.available":["2026-02-27T09:00:15Z"],"dc:date.issued":["2026-02-26"],"dc:description.abstract":["There are multiple pathways forward to next generation magnetic random access memory. In this thesis we explore two simple solutions with industry implementation in mind. The first is a low-damping (α< 5×10⁻³) ferromagnetic single-layer with modest anti-damping spin-orbit torque (SOT), $θ_{DL} ≈ 0.05. Here, we investigate an alternative approach to the traditional heavy metal/ferromagnet bilayer to produce SOTs, which suffers from high-damping that is detrimental to energy-efficiency. Instead, of breaking inversion symmetry at the interface we continually break symmetry along the thickness axis by creating an intentional compositional gradient that is purely ferromagnetic and maintains low damping. Crucially, we find that a compositional gradient is not necessary to achieve large damping-like SOTs, instead finding direct evidence from grazing-incidence x-ray diffraction for a strain gradient. The next pathway investigated is an easy-to-grow, polycrystalline alternative to non-collinear antiferromagnets which require high temperature growth (>400°C). We find that sputter-grown γ-FeMn with no post-annealing, has a small non-zero net magnetization (≈(0.02-0.07)μB/atom) and perpendicular magnetic anisotropy only slightly larger than those found in non-collinear antiferromagnets like Mn₃Sn while still exhibiting a large anomalous Hall conductivity of 14 S/cm at room temperature. We show that these unique magnetic and transport properties are the result of pinning at the grain boundaries which can be tuned to enhance the anomalous Hall conductivity."],"dc:description.abstractgeneral":["The spintronics community is searching for ways to make denser, faster, more power efficient and better enduring magnetic memory that can keep up with modern needs. One hurdle that this thesis addresses is how to minimize dissipation lost by magnetic friction while maintaining fast writing capabilities. The next is the issue of denser bits for magnetic memory, traditional ferromagnets have a stray field, like a horseshoe magnet in a sea of lead, which affects nearby components. This limits how tightly we can pack the bits that store our \"1\"s and \"0\"s in magnetic memory. An alternative path forward that is gaining interest is using antiferromagnets in magnetic memory as they have reduced stray fields. However, one of the issues is that because they do not have a large magnetic moment like in ferromagnets it can be hard to read the \"1\" and \"0\" states. This thesis offers a practical step forward with an inexpensive, easy-to-grow antiferromagnet that has the potential for large readout capabilities."],"dc:description.degree":["Doctor of Philosophy"],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:45716"],"dc:identifier.uri":["https://hdl.handle.net/10919/141583"],"dc:language.iso":["en"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["Spintronics","Anomalous Hall Effect","Spin Hall Effect","FMR","ST-FMR","antiferromagnets","low-damping"],"dc:title":["Practical Pathways to Efficient MRAM: Spin-Orbit Torques, Low-Damping, and Anomalous Hall Conductivity in Polycrystalline Materials"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:20:05Z"}