---
title: "GMR Spin Valve Interactive Lab | Sandbox Physics"
description: "How does rotating one magnetic layer change the resistance of a spin valve? The two magnetic layers scatter spin channels differently. Parallel magnetizations give a lower resistance, and antiparallel magnetizations give a higher resistance. At constant current, the changing resistance appears as a changing voltage."
canonical_url: "https://sandboxphysics.com/labs/gmr-spin-valve/"
language: "en"
page_type: "lab"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/labs/gmr-spin-valve/"
last_modified: "2026-10-24"
---

C-X3 · Turn a magnet, measure a voltage

# GMR Spin Valve

**How does rotating one magnetic layer change the resistance of a spin valve?** The two magnetic layers scatter spin channels differently. Parallel magnetizations give a lower resistance, and antiparallel magnetizations give a higher resistance. At constant current, the changing resistance appears as a changing voltage.

Rotate a free magnetic layer above a pinned reference and watch the carriers cross the metallic stack. Acquire a full angle scan and recover the parallel and antiparallel resistances from its voltage samples.

> Interactive simulation: open this page in a web browser to change the parameters and run the model.

This synthetic current-perpendicular-to-plane metallic spin valve uses a phenomenological cosine interpolation between specified parallel and antiparallel resistances. The free-layer angle is imposed in the film plane; the pinned layer points along the positive horizontal axis. A constant sense current converts resistance to voltage, with seeded independent Gaussian voltage noise. The fit uses stored samples. Carrier dots illustrate transport direction; their paths and spin colors do not solve microscopic scattering. The model omits magnetic hysteresis, domains, interlayer coupling, spin diffusion, spin torque, heating, anisotropic magnetoresistance and tunneling magnetoresistance. The real films are contiguous. Display gaps separate the enlarged layers for visibility and add no resistance. It is not a reconstruction of the original 1988 in-plane-current experiments.

Synthetic acquisition

## A full turn in voltage samples

Default record

> Interactive graph of synthetic acquired samples.

Saved amplifier samples

Fit to saved samples

The scan acquires the entire rotation. The apparatus above shows the current chosen angle.

Nobel · Condensed matter

## What did the original experiments establish?

Follow the apparatus, observations and interpretation in the historical evidence. Each article explains where this teaching model fits.

[Read the historical evidence](https://sandboxphysics.com/stories/condensed-matter/giant-magnetoresistance/) [All six reading paths](https://sandboxphysics.com/stories/condensed-matter/)

Physics tutorial

## Read a relative magnetic orientation electrically

**Background** A metallic spin valve contains two ferromagnetic films separated by a conducting spacer. One film is pinned; the other can rotate in its plane.

**Why it matters** A voltage measurement can reveal a magnetic orientation. An angular scan separates the resistance contrast from a single noisy reading.

Start with the essentials

- **Focus question**: How does rotating one magnetic layer change the resistance of a spin valve?
- **One-sentence intuition**: The relative magnetization angle changes the resistance, which a constant current converts into a voltage.

### Core mathematical model

#### Synthetic angular response

$$
R(\theta)=R_{\rm P}+\frac{R_{\rm AP}-R_{\rm P}}2(1-\cos\theta)
$$

The angle is between the two in-plane magnetizations. This phenomenological interpolation fixes the parallel and antiparallel limits.

#### Voltage at constant current

$$
V_k=I R(\theta_k)+\epsilon_k
$$

The stored voltage samples include independent Gaussian amplifier noise. The graph divides those samples by the known sense current.

#### Magnetoresistance contrast

$$
\mathrm{MR}=\frac{R_{\rm AP}-R_{\rm P}}{R_{\rm P}}
$$

The reported resistance limits come from fitting the saved scan to a constant plus a cosine.

### Common difficulties

#### Angle is not applied field

**Typical misconception** The resistance curve predicts a magnetic switching loop.

**Better mental model** This Lab imposes the angle. It does not calculate hysteresis, domains or the relation between field and magnetization.

#### A metallic spacer conducts

**Typical misconception** All spin valves work by tunneling through an insulating barrier.

**Better mental model** This GMR model uses a conducting spacer. An insulating tunnel junction has tunneling magnetoresistance and needs a different transport model.

### Run the experiment

1. 01

   #### Compare aligned and opposed magnets

   Select Easy passage and Opposed layers. Watch the free-layer arrow and compare resistance.

   **What to observe:** The pinned arrow stays fixed. Rotating the free arrow by half a turn changes the model from its lower to its higher resistance.

2. 02

   #### Record a full rotation

   Set a relative angle, then record an angle scan and export its voltage samples.

   **What to observe:** The live apparatus shows the chosen angle. The separate graph contains a complete acquired rotation, and its fit uses those saved readings.

3. 03

   #### Make the signal harder to read

   Choose Small magnetic contrast and compare scans at lower and higher sense current.

   **What to observe:** The resistance contrast shrinks. With fixed voltage noise, a larger current reduces the resistance uncertainty, although heating is outside this model.

Physical conclusion

The angular response measures a transport contrast. Inferring an applied field additionally requires a model of how the free magnet rotates.

Fields & matter · Starter path

## From a field to an electron microscope

Map an electric field and steer a charged particle. Then find the electron's wavelength and use electron beams to see a crystal and a surface.

[Start here → **Make an Electric Field Visible** Move the probe around a dipole and check that the field always points downhill on the potential landscape. Observe · 8 min](https://sandboxphysics.com/labs/electric-field/)

1. [1 Make an Electric Field Visible](https://sandboxphysics.com/labs/electric-field/)
2. [2 A Charge Bending through Fields](https://sandboxphysics.com/labs/charged-particle/)
3. [3 Electron Wavelength & Voltage](https://sandboxphysics.com/labs/electron-wavelength/)
4. [4 Electron Diffraction & Reciprocal Space](https://sandboxphysics.com/labs/electron-diffraction/)
5. [5 TEM Bright Field, Dark Field & SAED](https://sandboxphysics.com/labs/tem-mode-selector/)
6. [6 SEM Secondary-Electron Topography](https://sandboxphysics.com/labs/sem-topography/)

[View the full path →](https://sandboxphysics.com/topics/fields-and-matter/#starter-path)